Genotypic and phenotypic diversity in populations of plant-probiotic <Emphasis Type="Italic">Pseudomonas</Emphasis> spp. colonizing roots

Several soil microorganisms colonizing roots are known to naturally promote the health of plants by controlling a range of plant pathogens, including bacteria, fungi, and nematodes. The use of theses antagonistic microorganisms, recently named plant-probiotics, to control plant-pathogenic fungi is receiving increasing attention, as they may represent a sustainable alternative to chemical pesticides. Many years of research on plant-probiotic microorganisms (PPM) have indicated that fluorescent pseudomonads producing antimicrobial compounds are largely involved in the suppression of the most widespread soilborne pathogens. Phenotype and genotype analysis of plant-probiotic fluorescent pseudomonads (PFP) have shown considerable genetic variation among these types of strains. Such variability plays an important role in the rhizosphere competence and the biocontrol ability of PFP strains. Understanding the mechanisms by which genotypic and phenotypic diversity occurs in natural populations of PFP could be exploited to choose those agricultural practices which best exploit the indigenous PFP populations, or to isolate new plant-probiotic strains for using them as inoculants. A number of different methods have been used to study diversity within PFP populations. Because different resolutions of the existing microbial diversity can be revealed depending on the approach used, this review first describes the most important methods used for the assessment of fluorescent Pseudomonas diversity. Then, we focus on recent data relating how differences in genotypic and phenotypic diversity within PFP communities can be attributed to geographic location, climate, soil type, soil management regime, and interactions with other soil microorganisms and host plants. It becomes evident that plant-related parameters exert the strongest influence on the genotypic and phenotypic variations in PFP populations.     

Climate change, aerobiology, and public health in the Northeast United States

The epidemiological implications with respect to climate change and public health (e.g., shifts in disease vectors) are beginning to be acknowledged. Less recognized however, are the potential links between climate, plant biology and public health. In addition to being affected by climate (e.g., temperature determines plant range), carbon dioxide (CO₂) represents the raw material needed for photosynthesis and its rapid increase in the atmosphere is expected to stimulate plant growth. While there are a number of means by which plant biology intersects with human health (e.g., plant nutrition), one of the most widely recognized is aerobiology; specifically, the ability of plants to both produce pollen and to serve as a substrate for molds/fungi (e.g., sporulation). The current review represents an initial attempt to coalesce what is known regarding the likely impacts of climate/CO₂ on plant pollen/fungal spores and associated allergic disease that are, or could be, specific to the Northeast United States. Although the current results indicate a number of potentially unfavorable effects, we wish to stress that the current data are based on a small number of experiments. Additional data are crucial to both reduce epidemiological uncertainty and to derive a robust set of mitigation / adaptation strategies.     

Impact of parasite sympatry on the geographic mosaic of coevolution

Slave-making ants are specialized social parasites that steal the young from colonies of their host species to augment their slave supply. The degree of parasite-host specialization has been shown to shape the trajectory along which parasites and hosts coevolve and is a prime contributor to the geographic mosaic of coevolution. However, virtually nothing is known about extrinsic influences on parasite-host dynamics, although the simple addition of a competing slave-maker may significantly alter selection pressures. Here we report the effect of two sympatric slave-makers on a single host. We measured temporal and spatial changes in colonies of the primary host Temnothorax curvispinosus that had been placed in field enclosures along with a single colony of either one or both species of the North American slave-making ants Protomognathus americanus and Temnothorax duloticus. Each slave-maker species alone had a negative impact on its hosts, although one slave-maker species more frequently decimated its host assemblage and then went extinct. Nevertheless, the combined effect in mixed-parasite enclosures was, surprisingly, greatly attenuated. Virulent slave-maker growth and prudent slave-maker decay in these shared enclosures, together with field data showing an inverse proportional relationship between the two slave-makers in natural populations, suggest that their checkered distribution is a consequence of direct asymmetrical antagonism between parasites. Thus, our results imply a tripartite coevolutionary arms race, whereby intraguild interactions among social parasites strongly affect the realized selection pressures on hosts and contribute to the geographic mosaic of coevolution.     

Polychlorinated biphenyl congener patterns in tree swallows (Tachycineta bicolor) nesting in the Housatonic River watershed, western Massachusetts, USA, using a novel statistical approach

A novel application of a commonly used statistical approach was used to examine differences in polychlorinated biphenyl (PCB) congener patterns among locations and sample matrices in tree swallows (Tachycineta bicolor) nesting in the Housatonic River watershed in western Massachusetts, USA. The most prevalent PCB congeners in tree swallow tissue samples from the Housatonic River watershed were Ballsmitter Zell numbers 153, 138, 180, 187, 149, 101, and 170. These congeners were seven of the eight most prevalent congeners in Aroclor 1260, the PCB mixture that was the primary source of contamination in the Housatonic River system. Using paired-Euclidean distances and tolerance limits, it was demonstrated that congener patterns in swallow tissues from sites on the main stem of the Housatonic River were more similar to one another than to two sites upstream of the contamination or from a nearby reference area. The congener patterns also differed between the reference area and the two upstream tributaries and between the two tributaries. These pattern differences were the same in both pipper (eggs or just hatched nestlings) and 12-day-old nestling samples. Lower-chlorinated congeners appeared to be metabolized in nestlings and pippers compared to diet, and metabolized more in pippers compared to nestlings. Euclidean distances and tolerance limits provide a simple and statistically valid method to compare PCB congener patterns among groups.     

Practical survey on antibiotic-resistant bacterial communities in livestock manure and manure-amended soil

Through livestock manure fertilization, antibiotics, antibiotic-resistant bacteria and genes are transferred to agricultural soils, resulting in a high prevalence of antibiotic-resistant bacteria in the soil. It is not clear, however, whether a correlation exists between resistant bacterial populations in manure and manure-amended soil. In this work, we demonstrate that the prevalence of cephalexin-, amoxicillin-, kanamycin- and gentamicin-resistant bacteria as well as bacteria simultaneously resistant to all four antibiotics was much higher in manure-amended soils than in manure-free soil. 454-pyrosequencing indicated that the ARB and multiple antibiotic-resistant bacteria (MARB) in swine or chicken manure and manure-amended soil were mainly distributed among Sphingobacterium, Myroides, Enterococcus, Comamonas and unclassified Flavobacteriaceae. The genus Sphingobacterium was highly prevalent among ARB from swine manure and manure-amended soil, and was also the most dominant genus among MARB from chicken manure and manure-amended soil. Other dominant genera among ARB or MARB populations in manure samples, including Myroides, Enterococcus and Comamonas, could not be detected or were detected at very low relative abundance in manure-amended soil. The present study suggests the possibility of transfer of ARBs from livestock manures to soils and persistence of ARB in these environments.     

Removal of polycyclic aromatic hydrocarbons from aged-contaminated soil using cyclodextrins: experimental study

The removal of polycyclic aromatic hydrocarbons (PAHs) from soil using water as flushing agent is relatively ineffective due to their low aqueous solubility. However, addition of cyclodextrin (CD) in washing solutions has been shown to increase the removal efficiency several times. Herein are investigated the effectiveness of cyclodextrin to remove PAH occurring in industrially aged-contaminated soil. Beta-cyclodextrin (BCD), hydroxypropyl-beta-cyclodextrin (HPCD) and methyl-beta-cyclodextrin (MCD) solutions were used for soil flushing in column test to evaluate some influent parameters that can significantly increase the removal efficiency. The process parameters chosen were CD concentration, ratio of washing solution volume to soil weight, and temperature of washing solution. These parameters were found to have a significant and almost linear effect on PAH removal from the contaminated soil, except the temperature where no significant enhancement in PAH extraction was observed for temperature range from 5 to 35 degrees C. The PAHs extraction enhancement factor compared to water was about 200.     

The lack of microbial degradation of polycyclic aromatic hydrocarbons from coal-rich soils

Analytical techniques used to assess the environmental risk of contamination from polycyclic aromatic hydrocarbons (PAHs) typically consider only abiotic sample parameters. Supercritical fluid extraction and sorption enthalpy experiments previously suggested slow desorption rates for PAH compounds in two coal-contaminated floodplain soils. In this study, the actual PAH availability for aerobic soil microorganisms was tested in two series of soil-slurry experiments. The experimental conditions supported microbial degradation of phenanthrene if it was weakly sorbed onto silica gel. Native coals and coal-derived particles in two soils effectively acted as very strong sorbents and prevented microbial PAH degradation. The long history of PAH exposure and degree of coal contamination apparently had no influence on the capability of the microbial soil community to overcome constraints of PAH availability. Within the context of the experimental conditions and the compounds chosen, our results confirm that coal-bound PAHs are not bioavailable and hence of low environmental concern.     

Sources, fate, and toxic hazards of oxygenated polycyclic aromatic hydrocarbons (PAHs) at PAH-contaminated sites

In this paper we show that oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are important cocontaminants that should be taken into account during risk assessment and remediation of sites with high levels of PAHs. The presented data, which have been collected both from our own research and the published literature, demonstrate that oxy-PAHs are abundant but neglected contaminants at these sites. The oxy-PAHs show relatively high persistency and because they are formed through transformation of PAHs, their concentrations in the environment may even increase as the sites are remediated by methods that promote PAH degradation. Furthermore, we show that oxy-PAHs are toxic to both humans and the environment, although the toxicity seems to be manifested through other effects than those known to be important for polycyclic aromatic compounds in general, that is, mutagenicity and carcinogenicity. Finally, we present data that support the hypothesis that oxy-PAHs are more mobile in the environment than PAHs, due to their polarity, and thus have a higher tendency to spread from contaminated sites via surface water and groundwater. We believe that oxy-PAHs should be included in monitoring programs at PAH-contaminated sites, even if a number of other toxicologically relevant compounds that may also be present, such as nitro-PAHs and azaarenes, are not monitored. This is because oxy-PAH levels are difficult to predict from the PAH levels, because their environmental behavior differs substantially from that of PAHs, and oxy-PAHs may be formed as PAHs are degraded.     

Impact of Lime and Ash Applications on Soil Solution Chemistry of an Acidified Podzolic Soil

Soil solution samples were taken from two sites (Horröd and Hasslöv) in the south part of Sweden to evaluate how soil solution chemistry responded to different treatmentswith dolomite and wood ash. At Horröd, samples were taken four years after application of wood ash, 4.28 ton ha^-1 and dolomite, 3.25 ton ha^-1. At Hasslöv dolomite, 3.45 ton ha^-1 and 8.75 ton ha^-1 was applied and samples were taken 15 yr later. It was found that treatment with dolomite at one site (Hasslöv) resulted in higher pH values (<2 pH units) and higher nitrification. It was also found at this site that the total Al and the inorganic Al concentrations decreased with dolomite treatment. The Ca, Mg, DOC, Fe, SO₄ ^2- and Cl^- concentrations, mainly in the topsoil, were found to be higher at both sites, following dolomite treatment; Ca and Mg concentrations were 2–8 times higher (<820 M) than in controls (<70 M). Wood ash was found to have less impact. The PO₄ concentration in the O2 horizon at Hasslöv decreased due to dolomite-treatment. ANOVA (Analyse of Variance) and PLS (Partial Least Square) were used to evaluate the data from the two sites.