Biofilm cue for larval settlement in Hydroides elegans (Polychaeta): is contact necessary?

Larvae of many sessile marine invertebrates settle in response to surface microbial communities (biofilms), but the effects of soluble compounds from biofilms in affecting larval behavior prior to settlement, attachment, and metamorphosis have been little studied. This question was addressed by videotaping the behavior of competent larvae of the serpulid, Hydroides elegans, above settlement-inducing biofilms. Adult worms were collected in Pearl Harbor, Hawaii, USA in November 2012 and spawned almost immediately. Six-day old larvae were placed in five replicated treatments in small cups: (1) with a natural biofilm; (2) with a natural biofilm on an 8-µm screen, 1 mm above the bottom of a clean cup; (3) with a natural biofilm beneath a clean screen; (4) in a clean cup; and (5) in a clean cup with a clean screen. Using the videotapes, larval swimming speeds and trajectories were quantified within 5 min of the larvae being placed in a treatment. Only larvae that touched a biofilm, i.e., in treatments (1) and (2), slowed their swimming speed and increased the amount of time spent crawling rather than swimming. This shows that under these conditions, any soluble cues emanating from a biofilm do not affect settlement behavior. Furthermore, after 24 h close to 100 % of larva in the two accessible biofilm treatments had metamorphosed and <15 % in treatments that included a biofilm under a clean screen and no biofilm at all, strongly suggesting that soluble cues for settlement were not produced by the biofilms over the longer time period.     

Nitrogen fixation associated with the cyanobacterial mat of a marine laminated microbial ecosystem

The nitrogenase activity in the cyanobacterial mat of a laminated microbial ecosystem was investigated by the acetylene reduction method. Measurements under several conditions such as light and dark, aerobic and anaerobic and by inhibiting photosystem II by 10^-5 M DCMU showed the nitrogenase activity to be light stimulated and to some degree inhibited by oxygen. An appreciable amount of activity was also present under complete aerobic conditions. We estimated 8 to 15 kg N fixed per hectare per year for that part of the intertidal flat supporting growth of cyanobacteria. By measuring a vertical sediment profile, nitrogenase was shown to be associated with the cyanobacterial mat. Diurnal measurements of nitrogenase showed two activity peaks, one at sunrise and one at sunset. Following population dynamics in the cyanobacterial mat showed Microcoleus sp., Oscillatoria spp., Spirulina sp., Gloeocapsa sp. and sometimes Merismopedia sp. to be present. During four years of observations we never found any heterocystous cyanobacteria. Non-heterocystous cyanobacteria apparently play an important role in nitrogen fixation in this marine intertidal environment.     

Photosynthetic response to temperature and desiccation of the intertidal alga Mastocarpus papillatus

When exposed to air during low tide, intertidal macroalgae experience a terrestrial environment and often encounter extreme levels of heating and desiccation. Two aspects of photosynthesis may be influenced by this increase in temperature and decrease in water content during exposure to air: (1) the rate of aerial photosynthesis itself, and (2) the rate at which aquatic photosynthesis recovers upon immersion in water at high tide. This laboratory study examines the effect of air temperature and desiccation on photosynthesis of the intertidal macroalga Mastocarpus papillatus Kützing. Plants were collected at Hopkins Marine Station, California, USA (36°37N; 121°54W) between July and December 1990. When apical tips were exposed to 15 to 25°C air for 2 h, photosynthesis was rapidly recovered upon reimmersion in seawater. Recovery was delayed, but complete, when tissue was exposed to 30°C air, but did not occur after exposure to 35°C air. Desiccation did not influence either the rate or the ultimate level of recovery upon reimmersion. Photosynthesis in air generally decreased with increasing desication, with no net photosynthesis occurring below 25% relative water content. Net photosynthesis of hydrated thalli increased with air temperature from 15 to 30°C, then decreased at 35°C. Dark respiration of hydrated thalli increased over the entire temperature range. This study indicates that thallus heating and desiccation during periods of exposure to air can potentially influence the total carbon budget of M. papillatus.     

Assessment of oxidative and UV-C treatments for inactivating bacterial biofilms from groundwater wells

Microorganisms are ubiquitous in natural environments and in water supply infrastructure including groundwater wells. Sessile-state microorganisms may build up on well surfaces as biofilms and, if excessive, cause biofouling that reduces well productivity and water quality. Conditions can be improved using biocides and other traditional well rehabilitation measures; however, biofilm regrowth is inevitable given the continuous introduction of microorganisms from the surrounding environment. Alternative and less invasive well maintenance approaches are desirable for reducing biofilm densities while also minimizing harmful disinfection-by-products. The primary objective of this research was to evaluate effectiveness of alternative treatments for inactivating microorganisms comprising biofilms. A novel approach was designed for in situ growth of biofilms on steel coupons suspended from ‘chandeliers’. After more than 100 days of in situ growth, biofilms were harvested, sampled, and baseline biofilm densities quantified through cultivation. Ultraviolet-C (UV-C) and oxidative treatments including hydrogen peroxide (H₂O₂), ozone (O₃) and mixed oxidants were then applied to the biofilms in laboratory-scale treatments. Microbial inactivation was assessed by comparing treated versus baseline biofilm densities. H₂O₂ was the most effective treatment, and decreased density below baseline by as much as 3.1 orders of magnitude. Mixed oxidants were effective for the well having a lower density biofilm, decreasing density below baseline by as much as 1.4 orders of magnitude. Disparity in the response to treatment was apparent in the wells despite their spatial proximity and common aquifer source, which suggests that microbiological communities are more heterogeneous than the natural media from which they originate.     

Adaptations of Gracilaria pacifica (Rhodophyta) to nitrogen procurement at different intertidal locations

Nitrogen uptake, assimilation and accumulation were studied in three populations of Gracilaria pacifica Abbott in Bamfield Inlet, British Columbia, Canada, over three summers, 1979–1981. Two of these populations were in the intertidal one high and one low, and the third was a subtidal cultured population. Nitrate uptake rates, internal nitrate content and nitrate reductase activities were highest in the low intertidal population. Time-courses of uptake and uptake kinetics were studied. Both nitrate and ammonium were taken up simultaneously. Thalli from the high-intertidal population showed enhanced nitrate and ammonium uptake following mild desiccation, and greater tolerance to desiccation in terms of maintaining nitrogen uptake after severe desiccation. Transplants were made to determine the effect of intertidal height and geographic location on responses to desiccation, nitrogen uptake, assimilation and accumulation. Nitrate and ammonium uptake rates were dependent on intertidal height and geographic location. Transplanting up the intertidal increased nitrate uptake and nitrate reductase activity, but decreased the nitrate content of the thalli. There were few significant differences in ammonium uptake rates, and ammonium, amino acid, and soluble-protein content of the various populations. All high-intertidal populations, transplanted or natural, showed enhanced nitrate uptake rates following desiccation. Enhanced ammonium uptake rates following desiccation were restricted to the high-intertidal thalli in only one geographic location. Tolerance to higher levels of desiccation also appeared to be intertidal height-dependent, but required more than five weeks to fully develop or disappear.     

Larval metamorphosis of the mussel <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis> in response to <Emphasis Type="Italic">Alteromonas</Emphasis> sp. 1: evidence for two chemical cues?

Bacterial isolates from multi-species biofilms were identified by 16S rDNA gene sequences and investigated for their inductive effects as monospecific biofilms on larval metamorphosis of Mytilus galloprovincialis. Alteromonas sp. 1 biofilm was found to have inductive activity, which increased with increasing cell density. The cue(s) of Alteromonas sp. 1 biofilm responsible for inducing larval metamorphosis was further investigated. Treatment of the biofilm with formalin, ethanol, heat or ultraviolet irradiation resulted in a significant reduction in the inductive activity of Alteromonas sp. 1, and the crude extract of surface-bound products of the biofilm showed no activity. These results indicated that if the cue was a surface-bound chemical cue, it was unstable, or susceptible to the treatments or the extraction process. On the other hand, the inductive activity of treated biofilms had a linear regression to the cell survival of bacteria, indicating a metabolically active biofilm was a requirement for larval metamorphosis. Conditioned water of the biofilm did not induce larvae to metamorphose. However, larval crawling behavior in the conditioned water was the same as that in the biofilm prior to larval metamorphosis, and significantly different to larval behavior in seawater. This indicated that a potential or partial waterborne cue existed, but remained inactive when alone. A synergistic effect of the conditioned water with formalin-fixed Alteromonas sp. 1 biofilm resulted in a significant increase in larval metamorphosis. Heat treatment and fractionation of the conditioned water demonstrated that the waterborne cue was heat-stable and <3,000 Da in molecular weight. Platinum-coating, Lentil Lectin and Wheat Germ Agglutinin treatments of the formalin-fixed biofilm significantly reduced its synergistic effect with the conditioned water, suggesting that a surface-bound cue was present on the biofilm and that the cue might be associated with the bacterial exopolysaccharide or glycoprotein. Evidence presented here suggests that two chemical cues derived from bacteria act synergistically on larval metamorphosis of Mytilus galloprovincialis.     

Mapping the niche space of soil microorganisms using taxonomy and traits

The biodiversity of microbial communities has important implications for the stability and functioning of ecosystem processes. Yet, very little is known about the environmental factors that define the microbial niche and how this influences the composition and activity of microbial communities. In this study, we derived niche parameters from physiological response curves that quantified microbial respiration for a diverse collection of soil bacteria and fungi along a soil moisture gradient. On average, soil microorganisms had relatively dry optima (0.3 MPa) and were capable of respiring under low water potentials (-2.0 MPa). Within their limits of activity, microorganisms exhibited a wide range of responses, suggesting that some taxa may be able to coexist by partitioning the moisture niche axis. For example, we identified dry-adapted generalists that tolerated a broad range of water potentials, along with wet-adapted specialists with metabolism restricted to less-negative water potentials. These contrasting ecological strategies had a phylogenetic signal at a coarse taxonomic level (phylum), suggesting that the moisture niche of soil microorganisms is highly conserved. In addition, variation in microbial responses along the moisture gradient was linked to the distribution of several functional traits. In particular, strains that were capable of producing biofilms had drier moisture optima and wider niche breadths. However, biofilm production appeared to come at a cost that was reflected in a prolonged lag time prior to exponential growth, suggesting that there is a trade-off associated with traits that allow microorganisms to contend with moisture stress. Together, we have identified functional groups of microorganisms that will help predict the structure and functioning of microbial communities under contrasting soil moisture regimes.     

Drought stress,rain and recovery of the intertidal seaweed <Emphasis Type="Italic">Fucus spiralis</Emphasis>

Non-motile organisms of intertidal shores such as seaweeds have to cope with a great variability of environmental factors. In this survey, we studied whether different morphotypes of the intertidal seaweed Fucus spiralis L. are also reflected in a characteristic performance. Desiccation and recovery of this Phaeophyceae were investigated in field experiments near Aljezur, Portugal. Fucus spiralis is exposed to serious desiccation during periods of falling tide, resulting in a tissue water loss of about 90%. Due to large semidiurnal tidal ranges in this area, two morphotypes can be distinguished: F. spiralis growing in the lower intertidal (LZ) is thicker and fleshier compared with plants in the upper intertidal (HZ), and this is reflected in a significant difference in fresh and dry mass. During sunny days and at low tide, effective quantum yields (Φ_PSII) decreased significantly after 2 h desiccation. This continued until re-submersion. The photosynthetic performances of HZ and LZ plants also differed significantly after LZ plants were already submerged and photosynthetisizing, but the HZ specimens still exposed to air. Recovery experiments after desiccation treatments showed fast recovery within 6 min after re-submersion in both morphotypes. HZ specimens showed a slower recovery, which indicates a protection measure to the adverse conditions in the upper intertidal. In 24 h desiccation treatments, however, HZ specimens expressed a significantly higher maximum fluorescence yield F _v /F _m recovery. Simulated rainfalls during low tides caused photosynthetic activity to drop to 50% of initial F _v /F _m , independent of the length of the rain period. Treated plants also fully recovered after 6 min re-submersion in seawater. A comparison of single fronds and tufts clearly indicated advantages of the tuft growth strategy: tufts showed higher Φ_PSII at prolonged emersion times. Our study indicated a clear relationship between size and drought resistance, which was primarily due to the smaller and hardy HZ plants that withstand longer desiccation times without damage.     

Urban marine ecology in southern California: the ability of riprap structures to serve as rocky intertidal habitat

Increasing human populations along marine coastlines has lead to increasing urbanization of the marine environment. Despite decades of investigations on terrestrial ecosystems, the effect of urbanization on marine life is not well understood. Riprap is the rocky rubble used to build jetties, breakwaters, and armored shorelines. Roughly 30% of the southern California shoreline supports some form of riprap, while 29% of the shoreline is natural rocky substrate. Astonishingly few studies have investigated this anthropogenic rocky habitat even though it rivals a natural habitat in area on a regional scale along a coastline that has been extensively studied. In this study, I compared the diversity and community structure of exposed rocky intertidal communities on four riprap and four natural sites in southern California. I ask the following questions: (1) does diversity or community composition differ between intertidal communities on riprap and natural rocky habitats in southern California, (2) if so, which organisms contribute to those differences, (3) which physical factors are contributing to these differences, and (4) do riprap habitats support higher abundances of invasive species than natural habitats? On average, riprap and natural rocky habitats in wave exposed environments in southern California did not differ from each other in diversity or community composition when considering the entire assemblage. However, when only mobile species were considered, they occurred in greater diversity on natural shores. These differences appear to be driven by wave exposure. The presence of invasive species was negligible in both natural and riprap habitats.     

Effects of micro- and mesograzers on intertidal macroalgal recruitment

This study examined the effects of a guild of micrograzing harpacticoid copepods (dominated by two species of Paradactylopodia sp. nov. and one species of Scutellidium sp. nov.) and a mesograzing periwinkle, Afrolittorina praetermissa, on the early recruitment of intertidal macroalgae on a wave-exposed, rocky shore. This is the first study, to our knowledge, to examine the effects of micrograzers (<500 μm) on intertidal macroalgal recruitment. Data showed that microscopic harpacticoid copepods altered the assemblages and reduced the densities of several macroalgal taxa, while A. praetermissa changed the assemblages and reduced both the density and number of macroalgal taxa. Recruitment of encrusting coralline algae was actually higher in copepod inclusions than exclusions, suggesting that copepods may be beneficial to the recruitment of this algal group. These results contribute to the understanding of grazing as a factor causing high mortality of algal recruits, but also highlight the need for more studies that examine the effects of micro- and mesograzers on the distribution and abundance of macroalgae.     

Microbial interactions with the cyanobacterium Microcystis aeruginosa and their dependence on temperature

Associated heterotrophic bacteria alter the microenvironment of cyanobacteria and potentially influence cyanobacterial development. Therefore, we studied interactions of the unicellular freshwater cyanobacterium Microcystis aeruginosa with heterotrophic bacteria. The associated bacterial community was greatly driven by temperature as seen by DNA fingerprinting. However, the associated microbes also closely interacted with the cyanobacteria indicating changing ecological consequence of the associated bacterial community with temperature. Whereas concentration of dissolved organic carbon in cyanobacterial cultures changed in a temperature-dependent manner, its quality greatly varied under the same environmental conditions, but with different associated bacterial communities. Furthermore, temperature affected quantity and quality of cell-bound microcystins, whereby interactions between M. aeruginosa and their associated community often masked this temperature effect. Both macro- and microenvironment of active cyanobacterial strains were characterized by high pH and oxygen values creating a unique habitat that potentially affects microbial diversity and function. For example, archaea including ‘anaerobic’ methanogens contributed to the associated microbial community. This implies so far uncharacterized interactions between Microcystis aeruginosa and its associated prokaryotic community, which has unknown ecological consequences in a climatically changing world.     

Larval settlement and metamorphosis of the mussel <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis> in response to biofilms

Biofilms were allowed to develop on glass slips immersed 1.0–1.5 m below the sea surface in Tachibana Bay, Nagasaki, Japan, for different periods of time from November 2003 to January 2005. The effects of age, immersion month, dry weight, bacterial and diatom densities of these biofilms on the settlement and metamorphosis of pediveliger larvae of the mussel Mytilus galloprovincialis were investigated in the laboratory. Furthermore, biofilms were subjected to various treatments to investigate the nature of the settlement and metamorphosis cue in the biofilm. Pediveliger larvae of the mussel settled and metamorphosed in response to biofilms. Settlement and metamorphosis to the post-larval stage significantly increased with the biofilm age. In addition, the biofilm activity varied depending on the immersion month (season), e.g., for biofilms with the same age, those immersed between June and August had higher activities than those immersed between November and March. The activity of the biofilm also positively correlated with the dry weight, bacterial and diatom densities. These three quantitative parameters of the biofilm were significantly affected by the film age but were not affected by the immersion month, suggesting that other parameters (e.g., community structures, extracellular products) also affected the inductive activity of the biofilm. The fixative agents (formalin and glutaraldehyde), heat, ethanol, ultraviolet irradiation and antibiotics treatments of the biofilm resulted in significant reduction or loss of its inductive activity. The survival of bacterial cells in the treated films where activities were either reduced or lost also decreased significantly. No settlement and metamorphosis were obtained when larvae were exposed to the conditioned water of the biofilm. Thus, larvae of M. galloprovincialis settled and metamorphosed in response to a cue produced by living bacteria in the biofilm. The cue may be a bacterial extracellular product which was susceptible to the above treatments.     

Seaweed richness and herbivory increase rate of community recovery from disturbance

The importance of herbivores and of plant diversity for community succession and recovery from disturbance is well documented. However, few studies have assessed the relative magnitude of, or potential interactions between, these factors. To determine the combined effect of herbivory and surrounding algal species richness on the recovery of a rocky intertidal community, we conducted a 27-month field experiment assessing algal recruitment and succession in cleared patches that mimic naturally forming gaps in the ambient community. We crossed two herbivore treatments, ambient and reduced abundance, with monocultures and polycultures of the four most common algal species in a mid-high rocky intertidal zone of northern California. We found that both the presence of herbivores and high surrounding algal richness increased recovery rates, and the effect of algal richness was twice the magnitude of that of herbivores. The increased recovery rate of patches containing herbivores was due to the consumption of fast-growing, early colonist species that preempt space from perennial, late-successional species. Mechanisms linking algal richness and recovery are more numerous. In polycultures, herbivore abundance and species composition is altered, desiccation rates are lower, and propagule recruitment, survival, and growth are higher compared to monocultures, all of which could contribute the observed effect of surrounding species richness. Herbivory and species richness should jointly accelerate recovery wherever palatable species inhibit late-successional, herbivore-resistant species and recruitment and survival of new colonists is promoted by local species richness. These appear to be common features of rocky-shore seaweed, and perhaps other, communities.     

Effect of biological activated carbon filter depth and backwashing process on transformation of biofilm community

We studied BAC biofilm during the process of initial operation and backwash. Microbial diversity decreased gradually with the increase of BAC filter depth. Proteobacteria dominated at the phylum level among the BAC biofilm samples. α-proteobacteria increased about 10% in all carbon filter depth after backwash. The biological activated carbon (BAC) is a popular advanced water treatment to the provision of safe water supply. A bench-scale device was designed to gain a better insight into microbial diversity and community structure of BAC biofilm by using high-throughput sequencing method. Both samples of BAC biofilm (the first, third and fifth month) and water (inlet water and outlet water of carbon filter, outlet water of backwashing) were analyzed to evaluate the impact of carbon filter depth, running time and backwash process. The results showed that the microbial diversity of biofilm decreased generally with the increase of carbon filter depth and biofilm reached a steady-state at the top layer of BAC after three months’ running. Proteobacteria (71.02%–95.61%) was found to be dominant bacteria both in biofilms and water samples. As one of opportunistic pathogen, the Pseudomonas aeruginosa in the outlet water of device (1.20%) was about eight times higher than that in the inlet water of device (0.16%) at the genus level after five-month operation. To maintain the safety of drinking water, the backwash used in this test could significantly remove Sphingobacteria (from 8.69% to 5.09%, p<0.05) of carbon biofilm. After backwashing, the operational taxonomic units (OTUs) number and the Shannon index decreased significantly (p<0.05) at the bottom of carbon column and we found the Proteobacteria increased by about 10% in all biofilm samples from different filter depth. This study reveals the transformation of BAC biofilm with the impact of running time and backwashing.     

The effects of air exposure on the desiccation rate and photosynthetic activity of Thalassia hemprichii and Enhalus acoroides

The effects of air exposure on the desiccation rate and photosynthetic activity of Thalassia hemprichii and Enhalus acoroides were studied using chlorophyll fluorescence. The desiccation rate of T. hemprichii was higher than that of E. acoroides, while the critical threshold of relative water content (RWC_critical) showed opposite trend. Neither the desiccation rate nor RWC_critical of T. hemprichii was significantly affected by temperature, while the desiccation rate of E. acoroides was affected significantly. For both species, the effective photochemical efficiency of PSII decreased gradually above the RWC_critical, while declined rapidly below the RWC_critical. After initial air exposure, the relative maximum electron transport rate of both seagrasses increased gradually to a maximum and then decreased to initial value near the RWC_critical. Therefore, short-term air exposure above the RWC_critical is beneficial for both seagrasses, and the RWC_critical should be considered when examining the response of seagrass photosynthesis to air exposure and selecting transplantation sites.     

Environmental stresses and intertidal assemblages on hard substrates in the port of Long Beach,California, USA

Nine intertidal stations within the Port of Long Beach, California, USA, were sampled during September and October 1975 using the random point method and the scraping technique. A total of 96,168 individuals belonging to 55 taxa were recorded in the quantitative survey; qualitative scrapings included 136 taxa. The protected outer coast intertidal assemblages were found at all but three stations along the shoreline. The shoreline, being situated in between the more environmentally stressed inner harbor and the less stressed open ocean, supported assemblages characterized by an instability in species composition. The upper midlittoral zone was typically dominated by Chthamalus dalli, C. fissus and Balanus glandula. The lower midlittoral was colonized either by Anthopleura elegantissima-Prionotis lanceolata facies along the outer breakwater or by A. elegantissima-Tetraclita squamosa rubescens facies along the inner breakwater. The mussel bed, which is the characteristic assemblage of the Californian lower midlittoral zone was obscured by the competitors P. lanceolata, T. squamosa rubescens and A. elegantissima, and was thinned out by predators, of which Pisaster ochraceus was the most voracious. Suspension feeders were dominant in the upper midlittoral and producers and grazers in the lower midlittoral. Predators were few in number and restricted to levels below mean lower low water. There was a gradual increase in numbers of intertidal species and individual abundance from level +5 ft (1.5 m) to level +1 ft (0.3 m) and from shoreline to outer breakwater. This may be attributable to the decrease in environmental stresses in the lower water levels and the improvement in water quality from the inner to outer harbor area.     

Inhibition and facilitation of bryozoan and ascidian settlement by natural multi-species biofilms: effects of film age and the roles of active and passive larval attachment

Sessile marine invertebrate larvae can recognize suitable settlement substrata by using various environmental cues, including organic/microbial biofilms. In laboratory choice assays, the effect of biofilms of varying ages on the settlement behaviour of two fouling organisms was assessed. The species included the arborescent cheilostome bryozoan Bugula flabellata (Thompson) and the solitary ascidian Ciona intestinalis (L.), both of which are characteristic of temperate sublittoral hard substratum assemblages in northwest Europe. Experiments were carried out using polystyrene petri dish substrata preconditioned with multispecies biofilms from natural laboratory-aquarium seawater for 1, 3, 6 or 12 d. Unfilmed (new, initially sterile) dishes were used as control substrata. Whereas the coronate larvae of B. flabellata generally were inhibited by biofilming, irrespective of film age, the settlement of tadpole larvae of C. intestinalis was facilitated on biofilmed substrata, and numbers of settled larvae generally increased with biofilm age: the highest mean numbers were counted on 12 d-old biofilms. In C. intestinalis, settlement and metamorphosis are processes which can be temporally separate and are possibly induced by different environmental cues. This study therefore distinguished between C. intestinalis larvae which were attached to the biofilm surface by the anterior, and those larvae entrapped by the biofilm but not settled in the conventional meaning of the term. As reported in previous studies, we did observe that such entrapped larvae could subsequently attach and develop successfully into sessile juveniles. Both the numbers of “attached” and “trapped” tadpoles increased with biofilm age. Assuming that “settlement” is essentially a process involving the active behavioural response of larvae to environmental cues, it seems that the facilitated attachment of C. intestinalis onto biofilmed substrata is due to the combined effect of active habitat selection and passive deposition/“entrapment” of larvae onto the “sticky” substratum. Received: 21 August 1996 / Accepted: 21 November 1996     

Effects of exogenous acylated homoserine lactones on biofilms in biofilters for gaseous toluene treatment

● Biofilm formation was enhanced by exogenous AHLs. ● EPS production and microbial adhesive strength of biofilm were promoted. ● Exogenous AHLs improved the performance of biofilters treating toluene. Biofilters are typical biofilm reactors, and they usually have poor biofilm formation resulting in limited reactor performance. Exogenous acylated homoserine lactones (AHLs) can enhance biofilm formation in many bioreactors based on quorum sensing regulation. However, their effect on biofilm in biofilters utilized for volatile organic compound (VOC) removal is unknown and needs to be investigated. In this study, the effects of the exogenous AHLs on biofilters for gaseous toluene removal were investigated. Analysis of biofilms in biofilters showed that the addition of exogenous AHLs considerably enhanced biofilm growth; the average biofilm concentration increased by 18%. Furthermore, the average biofilm coverage proportions in biofilters with and without exogenous AHLs were 17 % and 13 %, respectively, demonstrating the positive effect of exogenous AHLs on biofilm coverage. In particular, exogenous AHLs promoted the production of extracellular polymeric substances and the microbial adhesive strength of the biofilm. In addition, the exogenous AHLs showed no significant effect on the gaseous toluene removal efficiency of the biofilter. These results show that exogenous AHLs can enhance biofilm formation and can guide the application of exogenous AHLs in VOC biofilters.     

Huddling up in a dry environment: the physiological benefits of aggregation in an intertidal gastropod

In many intertidal gastropods, the formation of aggregations and closing of the opercular opening are behaviors commonly assumed to be associated with water conservation and maintenance of body temperature during tidal emersion periods. In the laboratory, we quantified the relationship between these two behaviors in a littorinid snail common to the north-central shores of Chile, Echinolittorina peruviana, and evaluated any benefit of these behaviors during desiccating conditions. We predicted that solitary individuals would maintain their opercula open for less time than aggregated snails when exposed to drier conditions due, at least in part, to differences in evaporative water loss. In laboratory trials, where relative humidity was manipulated, we observed that aggregated snails maintained their opercula open for longer periods of time than solitary snails under increasingly drier conditions. These results, together with observations of body temperature, suggest that aggregated animals may able to maintain gaseous exchange with their environment for longer periods of time than solitary individuals in response to desiccation stress. Our results suggest an interactive effect of two behaviors that confer physiological benefits when confronted with extreme physical conditions experienced during periods of emersion.     

两座高原水库蓝藻群落结构与微囊藻毒素的分布对比研究

为了了解贵州高原水库蓝藻群落组成特征和微囊藻毒素分布,于2009年10月对贵州高原2座水库——万峰湖和百花湖采样调查。结果表明：万峰湖以蓝藻为主要优势藻,蓝藻中的拟柱孢藻（Cylindrospermopsis sp.）占绝对优势,浮游植物丰度在13.05×104～55.80×104 cells.L-1之间,蓝藻的丰度值占到了总量的82.55%,6个采样点中有3个（大坝、野鸭滩和革布）检出了微囊藻毒素MC-RR,且有1个点（革布）质量浓度超标,另外3个点（坝艾、坝达章和九里堡）未检出;百花湖以蓝藻、绿藻和硅藻共同构成优势藻,蓝藻中的假鱼腥藻（Pseudanabaena limnetica）是主要优势藻,浮游植物丰度在6.16×104～65.00×104 cells.L-1之间,蓝藻的丰度值在总体中所占比例为33.25%,3个采样点（大坝、岩脚寨和码头）均未检出微囊藻毒素。形成2个高原水库蓝藻群落结构和微囊藻毒素分布差异的原因可能是：2个水库中氮、磷营养盐水平不同引起浮游植物群落组成不同,进而导致了微囊藻毒素的分布出现差异。