Improvement of aquaculture water quality by mixed Bacillus and its effects on microbial community structure

Microbial remediation, especially the application of probiotics, has recently gained popularity in improving water quality and maintaining aquatic animal health. The efficacy and mechanism of mixed Bacillus for improvement of water quality and its effects on aquatic microbial community structure remain unknown. To elucidate these issues, we applied two groups of mixed Bacillus (Bacillus megaterium and Bacillus subtilis (A0?+?BS) and Bacillus megaterium and Bacillus coagulans (A0?+?BC)) to the aquaculture system of Crucian carp. Our results showed that the improvement effect of mixed Bacillus A0?+?BS on water quality was better than that of A0?+?BC, and the NH₄⁺-N, NO₂^?-N, NO₃^?-N, and total phosphorus (TP) concentrations were reduced by 46.3%, 76.3%, 35.6%, and 80.3%, respectively. In addition, both groups of mixed Bacillus increased the diversity of the bacterial community and decreased the diversity of the fungal community. Microbial community analysis showed that mixed Bacillus A0?+?BS increased the relative abundance of bacteria related with nitrogen and phosphorus removal, such as Proteobacteria, Actinobacteria, Comamonas, and Stenotrophomonas, but decreased the relative abundance of pathogenic bacteria (Acinetobacter and Pseudomonas) and fungi (Epicoccum and Fusarium). Redundancy analysis showed that NH₄⁺-N, NO₂^?-N, and TP were the primary environmental factors affecting the microbial community in aquaculture water. PICRUST analysis indicated that all functional pathways in the A0?+?BS group were richer than those in other groups. These results indicated that mixed Bacillus A0?+?BS addition produced good results in reducing nitrogenous and phosphorus compounds and shaped a favorable microbial community structure to further improve water quality.

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The effects of extracellular algicidal compounds of Bacillus sp. B1 on Heterosigma akashiwo: a metabolomics approach

Heterosigma akashiwo (H. akashiwo), a harmful algal species, has been a global environmental problem. Extracellular algicidal compounds (EACs) extracted from Bacillus sp. B1 exhibited algicidal effects against H. akashiwo. However, little is known about the algicidal mechanism and metabolic process. In this study, metabolomics and physiological analyses were combined to investigate the cellular responses of H. akashiwo when treated with EACs. The results indicated that EACs at 10% (v_EACs/v_sample) showed more than 90% inhibition of H. akashiwo. EAC treatment resulted in excessive reactive oxygen species (ROS) production in algal cells, causing stress responses such as inhibition of photosynthetic pigment synthesis, reduction of sugar synthesis, imbalance of osmotic pressure in the cell membrane, disruption of cell size and morphology, and eventual cell death. The results reveal the underlying mechanism of the algicidal process and provide new insights into algae-bacteria interactions and the application of metabolomics to algal research.

     

Cell wall surface layer (S-layer) promotes colony formation in Microcystis: comparison of S-layer characteristics between colonial and unicellular forms of Microcystis and function conformation

Colony is a key to Microcystis becoming a dominant population and forming blooms. To find the mechanism of colony formation, we investigated cell wall structures of colonial and unicellular strains. Results showed that colonial strains had significant surface layer protein (S-layer) on the surface of cells than unicellular strains by transmission electron microscopy. Western blot showed colonial strains had more S-layer than the unicellular strains. When the S-layer gene (GenBank accession number CAO89090.1) of Microcystis aeruginosa PCC7806 was expressed in Synechocystis sp. PCC6803, PCC6803 aggregated into colonial morphology. The results indicated that the S-layer could promote colony formation in Microcystis. Based on the S-layer sequences of PCC6803 and PCC7806, nine S-layer genes in other Microcystis strains were screened from the GenBank. Sequence comparing showed that the S-layers conserved regions were all located in N-terminal. The S-layers contain repeats-in-toxin (RTX) sequences with Ca²⁺-binding site, and their amino acid composition, hydrophobicity, isoelectric point, etc. were consistent with the characteristics of RTX-type S-layer in bacteria.

     

Effects of fenvalerate concentrations and its chiral isomers on bacterial community structure in the sediment environment of aquaculture ponds

To investigate the effect of chiral pesticide fenvalerate (FV) on the micro-ecological environment of aquaculture pond sediment, we used an indoor static experiment to observe the effects of FV added at different concentrations with different chiral isomers on the changes in the sediment bacterial community. The 16S rDNA high-throughput sequencing technique was used to conduct sequencing and analysis of the bacterial community structure as well as changes in aquaculture pond sediments after 4 weeks of cultivation. The results showed that the microbial alpha diversity indices (Sobs and Shannon indices) of the treated groups were significantly lower than those of the control group after 4 weeks (P < 0.05), and the values in the high-concentration group were significantly lower than those of the low-concentration group (P < 0.05). In terms of bacterial group composition, the proportion of abundance of Proteobacteria and Acidobacteria in the treated groups were greater than in the control group after 4 weeks, while the proportion of abundance of Bacteroidetes and Verrucomicrobia were lower. In the high-concentration FV treatment group, the proportion of abundance of Bacteroidetes, Acidobacteria, Chloroflexi, Nitrospinae, unclassified_k_norank, Ignavibacteriae, and Nitrospirae were significantly different from those of the other groups (P < 0.05). Principal coordinate analysis (PCoA) and ANONISIM/Adonis analysis showed that the cis-enantiomer had a stronger effect on the bacterial community as the concentration of FV increased. In addition, the linear discriminant analysis effect size (LEfSe) and linear discriminant analysis (LDA) results revealed differences in the level of enrichment of bacterial groups caused by FV at different concentrations and isomer levels. Collectively, this study showed that FV residue has a pronounced effect on bacterial communities in sediment, which becomes more significant with increasing exposure concentration. The effects of the cis- and trans-enantiomers of FV on the sediment environment are different; the cis-enantiomer has a stronger effect on the bacterial community.

     

Effects of suspended solids on cyanobacterial bloom formation under different wind fields

Wind waves and suspended solids (SS) generated by the resuspension of sediments are ubiquitous characteristics of lake ecosystems. However, their effects on phytoplankton remain poorly elucidated in shallow eutrophic lakes. Laboratory experiments were carried out to investigate the responses of Microcystis aeruginosa to SS under static (wind speed of 0 m/s) and breeze (wind speed of 3 m/s) conditions. Results showed that 50 mg/L SS can promote the growth of M. aeruginosa, accelerate the formation of colonies, and increase the floating rate under no-wind conditions. Comparing with static environment, breeze can significantly increase the growth rate of M. aeruginosa and benefit the formation of larger colonies of algae cells. Driven by wind and SS, the buoyancy of the cyanobacteria community in different experimental groups was obviously different. The specific performance was that low SS concentration and breeze were in favor of the floating of cyanobacteria, while high SS concentration went against the floating of algal cells. As a conclusion, wind speed of 3 m/s and 20–50 mg/L SS have a synergistic effect on the formation of cyanobacterial blooms. This study can provide an improved current understanding of bloom formation and turbidity management strategies in shallow eutrophic lakes.

     

Isolation and characterization of mesotrione-degrading Bacillus sp. from soil

Dissipation kinetics of mesotrione, a new triketone herbicide, sprayed on soil from Limagne (Puy-de-Dôme, France) showed that the soil microflora were able to biotransform it.Bacteria from this soil were cultured in mineral salt solution supplemented with mesotrione as sole source of carbon for the isolation of mesotrione-degrading bacteria. The bacterial community structure of the enrichment cultures was analyzed by temporal temperature gradient gel electrophoresis (TTGE). The TTGE fingerprints revealed that mesotrione had an impact on bacterial community structure only at its highest concentrations and showed mesotrione-sensitive and mesotrione-adapted strains. Two adapted strains, identified as Bacillus sp. and Arthrobacter sp., were isolated by colony hybridization methods.Biodegradation assays showed that only the Bacillus sp. strain was able to completely and rapidly biotransform mesotrione. Among several metabolites formed, 2-amino-4-methylsulfonylbenzoic acid (AMBA) accumulated in the medium. Although sulcotrione has a chemical structure closely resembling that of mesotrione, the isolates were unable to degrade it.     

Contamination of antibiotic resistance genes (ARGs) in a typical marine aquaculture farm: source tracking of ARGs in reared aquatic organisms

Abstract

Although the prevalence and concentrations of antibiotic resistance genes (ARGs) in aquaculture is receiving increasing scientific interest, there is little understanding of the direct sources and dissemination pathways of ARGs in marine aquaculture-reared organisms. This study investigated the dynamics of ARGs and the bacterial community throughout the rearing period in a typical marine aquaculture farm in South China. The results demonstrated that sul1 and qnrD were predominant in the sediment, and qnrD and qnrA were predominant in the intestinal tracts of shrimps. Network analysis showed that the chemical oxygen demand, total organic carbon, dissolved organic carbon, suspended solids, and total phosphorus were positively correlated with the predominant ARGs. The results of the network and source tracking analyses indicate that environmental factors and the bacterial community may drive the dissemination of ARGs dissemination in the environment and in shrimp reared by marine aquaculture, and sediment is the most direct and important medium in this dissemination. These results aid in improving our understanding of the sources, level, and dissemination of ARGs in marine aquaculture.     

Effects of a sulfonylurea herbicide on the soil bacterial community

Sulfonylurea herbicides are widely used on a wide range of crops to control weeds. Chevalier® OnePass herbicide is a sulfonylurea herbicide intensively used on cereal crops in Algeria. No information is yet available about the biodegradation of this herbicide or about its effect on the bacterial community of the soil. In this study, we collected an untreated soil sample, and another sample was collected 1 month after treatment with the herbicide. Using a high-resolution melting DNA technique, we have shown that treatment with Chevalier® OnePass herbicide only slightly changed the composition of the whole bacterial community. Two hundred fifty-nine macroscopically different clones were isolated from the untreated and treated soil under both aerobic and microaerobic conditions. The strains were identified by sequencing a conserved fragment of the 16S rRNA gene. The phylogenetic trees constructed using the sequencing results confirmed that the bacterial populations were similar in the two soil samples. Species belonging to the Lysinibacillus, Bacillus, Pseudomonas, and Paenibacillus genera were the most abundant species found. Surprisingly, we found that among ten strains isolated from the treated soil, only six were resistant to the herbicide. Furthermore, bacterial overlay experiments showed that only one resistant strain (related to Stenotrophomonas maltophilia) allowed all the sensitive strains tested to grow in the presence of the herbicide. The other resistant strains allowed only certain sensitive strains to grow. On the basis of these results, we propose that there must be several biodegradation pathways for this sulfonylurea herbicide.     

Co-regulatory role of Microcystis colony cell volume and compactness in buoyancy during the growth stage

The buoyancy of Microcystis colonies determines the occurrence and dominance of bloom on the water surface. Besides the cell density regulation and the formation of larger size aggregates, increases in cell volume per colony (V_cell) and the colony’s compactness (i.e., volume ratio of cells to the colony, VR) may promote Microcystis colony buoyancy. Yet only a few studies have studied the relationship between the internal structure variation of colonies and their buoyancy, and the co-regulatory role of V_cell and VR of Microcystis colonies in the floating velocity (FV) remains largely unexplored. In the present study, we optimized a method for measuring the compactness of Microcystis colonies based on the linear relationship between total V_cell and chlorophyll a. Different relationships between the VRs and FVs were observed with different colony size and V_cell range groups. Both field and laboratory experiments showed that FV/(D₅₀, median diameter)² had a significant linear relationship with VR, indicating that the cell density and extracellular polysaccharides were unchanged over a short time period and could be estimated via the slope and intercept of a fitted line. We also constructed a functional relationship between FV, VR, and V_cell and found that high VR and V_cell can promote Microcystis buoyancy. This means that increasing cell compactness or V_cell may be an active regulation strategy for Microcystis colonies to promote buoyancy. Therefore, quantifying the internal structure of Microcystis colonies is strongly recommended for the assessment of Microcystis bloom development and their management.

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Biodegradation of soil‐applied endosulfan in the presence of a biosurfactant

Abstract

Biodegradation of endosulfan isomers in soil‐applied and flask‐coated conditions was studied, by an isolated bacterial coculture. The degradation in soil‐applied form was 20–30% slower than in flask‐coated condition. Addition of a biosurfactant, isolated from Bacillus subtilis MTCC 1427, enhanced the rate of biodegradation by 30–45% in both the conditions. It also mobilized the residual endosulfan towards biodegradation, that otherwise remains undegraded.     

A Simple Technique for Stack Design in Complex Terrain

The main objective of this study is to apply neutral electrolyzed water (NEW) spraying to inactivate bioaerosols. We evaluated the inactivation efficiency of NEW applied to inactivate two airborne bacterial Escherichia coli and Bacillus subtilis aerosols inside an environmental-controlled chamber in the study. Generated with electrolyzing 6.15 M sodium chloride brine, the NEW with free available chlorine (FAC) concentration 50, 100, and 200 ppm was pumped with an air pressure of 70 kg/cm² through nozzle into the chamber to inactive E. coli and B. subtilis aerosols precontaminated air (initial counts of 3?×?10⁴ colony-forming units [CFU]/m³). Bacterial aerosols were collected and cultured from chamber before and after NEW spray. The air exchange rate (ACH, hr^?1) of the chamber was set to simulate fresh air ventilating dilution of indoor environment. First-order concentration decaying coefficients (Ka, min^?1) of both bacterial aerosols were measured as an index of NEW inactivation efficiency. The result shows that higher FAC concentration of NEW spray caused better inactivation efficiency. The Ka values under ACH 1.0 hr^?1 were 0.537 and 0.598 for E. coli of FAC 50 and 100 ppm spraying, respectively. The Ka values of FAC 100 ppm and 200 ppm spraying for B. subtilis were 0.063 and 0.085 under ACH 1.0 hr^?1, respectively. The results indicated that NEW spray is likely to be effective in inactivation of bacterial airborne contamination. Moreover, it is observed in the study that the increase of ventilation rate and the use of a larger orifice-size nozzle may facilitate the inactivation efficiency.

Implications: Bacterial aerosols have been implicated in deterioration of air quality and occupational health. Effective, safe, and economic control technology is highly demanded, especially for agricultural and food industries. In the study, NEW mist spraying performed effectively in controlling E. coli and B. subtilis modeling bioaerosols contamination. The NEW revealed its potential as an alternative airborne disinfectant worth being discovered for improving the environmental quality in the future.     

Shaping effects of rice,wheat, maize,and soybean seedlings on their rhizosphere microbial community

The rhizosphere microbiome plays critical roles in plant growth and is an important interface for resource exchange between plants and the soil environment. Crops at various growing stages, especially the seedling stage, have strong shaping effects on the rhizosphere microbial community, and such community reconstruction will positively feed back to the plant growth. In the present study, we analyzed the variations of bacterial and fungal communities in the rhizosphere of four crop species: rice, soybean, maize, and wheat during successive cultivations (three repeats for the seedling stages) using 16S rRNA gene and internal transcribed spacer (ITS) high-throughput sequencing. We found that the relative abundances of specific microorganisms decreased after different cultivation times, e.g., Sphingomonas, Pseudomonas, Rhodanobacter, and Caulobacter, which have been reported as plant-growth beneficial bacteria. The relative abundances of potential plant pathogenic fungi Myrothecium and Ascochyta increased with the successive cultivation times. The co-occurrence network analysis showed that the bacterial and fungal communities under maize were much more stable than those under rice, soybean, and wheat. The present study explored the characteristics of bacteria and fungi in crop seedling rhizosphere and indicated that the characteristics of indigenous soil flora might determine the plant growth status. Further study will focus on the use of the critical microorganisms to control the growth and yield of specific crops.

     

The microbiota of an unpolluted calcareous soil faces up chlorophenols: Evidences of resistant strains with potential for bioremediation

To highlight the effects of a variety of chlorophenols (CP) in relation to the response of an indigenous bacterial community, an agricultural Mediterranean calcareous soil has been studied in microcosms incubated under controlled laboratory conditions. Soil samples were artificially polluted with 2-monochlorophenol (MCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP), at concentrations ranging from 0.1 up to 5000 mg kg⁻¹. Both activity and composition of the microbial community were assessed during several weeks, respectively, by respirometric methods and PCR-DGGE analysis of extracted DNA and RNA. Significant decreases in soil respirometric values and changes in the bacterial community composition were observed at concentrations above 1000 mg kg⁻¹ MCP and TCP, and above 100 mg kg⁻¹ PCP. However, the persistence of several active bacterial populations in soil microcosms contaminated with high concentration of CP, as indicated by DGGE fingerprints, suggested the capacity of these native bacteria to survive in the presence of the pollutants, even without a previous adaptation or contact with them.The isolation of potential CP degraders was attempted by culture plating from microcosms incubated with high CP concentrations. Twenty-three different isolates were screened for their resistance to TCP and PCP. The most resistant isolates were identified as Kocuria palustris, Lysobacter gummosus, Bacillus sp. and Pseudomonas putida, according to 16S rRNA gene homology. In addition, these four isolates also showed the capacity to reduce the concentration of TCP and PCP from 15% to 30% after 5 d of incubation in laboratory assays (initial pollutant concentration of 50 mg L⁻¹). Isolate ITP29, which could be a novel species of Bacillus, has been revealed as the first known member in this bacterial group with potential for CP bioremediation applications, usually wide-spread in the soil natural communities, which has not been reported to date as a CP degrader.     

Antibacterial activity of different natural honeys from Transylvania,Romania

Honey is used in food industry and medicine due to its nutritive, therapeutic and dietetic qualities. The microbiological characteristics of 10 unpasteurized honey samples of known origin, collected from Transylvania beekeepers (Romania) were determined. The antibacterial activity of these types of honey against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, Salmonella enteritidis, Salmonella anatum, Salmonella choleraesuis, Bacillus cereus, Bacillus subtilis subsp. spizizenii and Listeria monocytogenes strains was studied. The most sensitive to the antibacterial activity were the two staphylococus strains (the largest diameter of inhibition zone was 18 mm) and B. subtilis strains (13.5 mm). The strains of B. cereus, E. coli, L. monocytogenes and Salmonella spp. were found to present resistance to some of the honey samples. Manna, sunflower and polyfloral honeys presented high antibacterial activity while acacia and linden honeys had a lower activity in terms of the number of sensible strains. Statistical analysis shows that the type of strains and the type of honey have influence on the diameter of inhibition.     

Quantification and Analysis of Airborne Bacterial Characteristics in a Nursing Care Institution

ABSTRACT

Indoor air quality has become a critical issue because people spend most of their time in the indoor environment. The factors that influence indoor air quality are very important to environmental sanitation and air quality improvement. This study focuses on monitoring air quality, colony counts, and bacteria species of the indoor air of a nursing care institution. The regular colony counts in two different wards range from 55 to 600 cfu m^?3. Regression analysis results indicate that the bacterial colony counts have close correlation with relative humidity or carbon dioxide (CO₂) but not with carbon monoxide (CO) or ozone (O₃). Real-time PCR was used to quantify the bacterial pathogens of nosocomial infection, including Acinetobacter baumannii, Citrobacter freundii, Escherichia coli, Klebsiella pneumoniae, and methicillin-sensitive Staphylococcus aureus. The most abundant bacteria species in the air of the nursing care institution is E. coli.

IMPLICATIONS Indoor temperature, humidity, ventilation, accumulation of biological pollutants, and potential infection problems will seriously affect the indoor environments. Studying these factors is important to indoor environmental sanitation and air quality improvements. Results of using real-time PCR to evaluate the bacterial pathogens of nosocomial infection for a nursing care institution in Taiwan reveal that the main bacteria species existing in the indoor air is E. coli.     

Bacterial community structure and diversity responses to the direct revegetation of an artisanal zinc smelting slag after 5 years

This comparative field study examined the responses of bacterial community structure and diversity to the revegetation of zinc (Zn) smelting waste slag with eight plant species after 5 years. The microbial community structure of waste slag with and without vegetation was evaluated using high-throughput sequencing. The physiochemical properties of Zn smelting slag after revegetation with eight plant rhizospheres for 5 years were improved compared to those of bulk slag. Revegetation significantly increased the microbial community diversity in plant rhizospheres, and at the phylum level, Proteobacteria, Acidobacteria, and Bacteroidetes were notably more abundant in rhizosphere slags than those in bulk waste slag. Additionally, revegetation increased the relative abundance of plant growth-promoting rhizobacteria such as Flavobacterium, Streptomyces, and Arthrobacter as well as symbiotic N₂ fixers such as Bradyrhizobium. Three dominant native plant species (Arundo donax, Broussonetia papyrifera, and Robinia pseudoacacia) greatly increased the quality of the rhizosphere slags. Canonical correspondence analysis showed that the differences in bacterial community structure between the bulk and rhizosphere slags were explained by slag properties, i.e., pH, available copper (Cu) and lead (Pb), moisture, available nitrogen (N), phosphorus (P), and potassium (K), and organic matter (OM); however, available Zn and cadmium (Cd) contents were the slag parameters that best explained the differences between the rhizosphere communities of the eight plant species. The results suggested that revegetation plays an important role in enhancing bacterial community abundance and diversity in rhizosphere slags and that revegetation may also regulate microbiological properties and diversity mainly through changes in heavy metal bioavailability and physiochemical slag characteristics.

     

The exposition of a calcareous Mediterranean soil to toxic concentrations of Cr, Cd and Pb produces changes in the microbiota mainly related to differential metal bioavailability

The involvement of the bacterial community of an agricultural Mediterranean calcareous soil in relation to several heavy metals has been studied in microcosms under controlled laboratory conditions. Soil samples were artificially polluted with Cr(VI), Cd(II) and Pb(II) at concentrations ranging from 0.1 to 5000 mg kg⁻¹ and incubated along 28 d. The lowest concentrations with significant effects in soil respirometry were 10 mg kg⁻¹ Cr and 1000 mg kg⁻¹ Cd and Pb. However, only treatments showing more than 40% inhibition of respirometric activity led to significant changes in bacterial composition, as indicated by PCR-DGGE analyses. Presumable Cr- and Cd-resistant bacteria were detected in polluted microcosms, but development of the microbiota was severely impaired at the highest amendments of both metals. Results also showed that bioavailability is an important factor determining the impact of the heavy metals assayed, and even an inverted potential toxicity ranking could be achieved if their soluble fraction is considered instead of the total concentration. Moreover, multiresistant bacteria were isolated from Cr-polluted soil microcosms, some of them showing the capacity to reduce Cr(VI) concentrations between 26% and 84% of the initial value. Potentially useful strains for bioremediation were related to Arthrobacter crystallopoietes, Stenotrophomonas maltophilia and several species of Bacillus.     

Microbial diversity,community composition and metabolic potential in hydrocarbon contaminated oily sludge: prospects for in situ bioremediation

Microbial community composition and metabolic potential have been explored in petroleum-hydrocarbon-contaminated sludge of an oil storage facility. Culture-independent clone library-based 16S rRNA gene analyses revealed that the bacterial community within the sludge was dominated by the members of β-Proteobacteria (35 %), followed by Firmicutes (13 %), δ-Proteobacteria (11 %), Bacteroidetes (10 %), Acidobacteria (6 %), α-Proteobacteria (3 %), Lentisphaerae (2 %), Spirochaetes (2 %), and unclassified bacteria (5 %), whereas the archaeal community was composed of Thermoprotei (54 %), Methanocellales (33 %), Methanosarcinales/Methanosaeta (8 %) and Methanoculleus (1 %) members. Methyl coenzyme M reductase A (mcrA) gene (a functional biomarker) analyses also revealed predominance of hydrogenotrophic, methanogenic Archaea (Methanocellales, Methanobacteriales and Methanoculleus members) over acetoclastic methanogens (Methanosarcinales members). In order to explore the cultivable bacterial population, a total of 28 resident strains were identified and characterized in terms of their physiological and metabolic capabilities. Most of these could be taxonomically affiliated to the members of the genera Bacillus, Paenibacillus, Micrococcus, Brachybacterium, Aerococcus, and Zimmermannella, while two strains were identified as Pseudomonas and Pseudoxanthomonas. Metabolic profiling exhibited that majority of these isolates were capable of growing in presence of a variety of petroleum hydrocarbons as sole source of carbon, tolerating different heavy metals at higher concentrations (≥1 mM) and producing biosurfactant during growth. Many strains could grow under a wide range of pH, temperature, or salinity as well as under anaerobic conditions in the presence of different electron acceptors and donors in the growth medium. Correlation between the isolates and their metabolic properties was estimated by the unweighted pair group method with arithmetic mean (UPGMA) analysis. Overall observation indicated the presence of diverse groups of microorganisms including hydrocarbonoclastic, nitrate reducing, sulphate reducing, fermentative, syntrophic, methanogenic and methane-oxidizing bacteria and Archaea within the sludge community, which can be exploited for in situ bioremediation of the oily sludge.     

Antibiotic resistance and genetic diversity of Escherichia coli isolates from traditional and integrated aquaculture in South China

This study investigated antibiotic resistance profiles including antibiotic resistance frequencies, resistance genes and resistance patterns in Escherichia coli strains isolated from traditional and integrated aquaculture systems in South China by using antibiotic susceptibility testing and real time polymerase chain reaction (PCR) technique. The E. coli isolates were found to be resistant to at least one antibiotic among 12 antibiotics. Higher resistance frequencies to ampicillin, sulfamethoxazole, trimethoprime, streptomycin and tetracycline were found compared to the rest antibiotics. Among the 10 tetracycline resistance genes detected in the resistant isolates, the most prevalent tetracycline resistance genes were tetA, tetW and tetB with the frequency of 69.7%, 63.5% and 21.9%, respectively. Three sulfonamide resistance genes were detected in these resistant isolates, with their detection frequencies in the following order: sul2 (55.3%) > sul3 (28.2%) > sul1 (6.2%). Four resistance genes mainly encoding extended-spectrum β-lactamases (ESBLs) were detected in these resistant isolates, with the detection frequencies of blaTEM (28.4%) > blaOXA (9.7%) > blaCTX (9.3%) > blaCARB (5.2%) > blaSHV (0.0%). It was found that the integrated aquaculture system exhibited generally higher prevalence of antibiotic resistance than the traditional aquaculture system. An integrated aquaculture system could facilitate development of bacterial resistance and spread of the antibiotic resistance genes, and consequently become an important reservoir of resistance genes.     

A comparison of antibiotics,antibiotic resistance genes,and bacterial community in broiler and layer manure following composting

Animal manure is an important source of antibiotics and antibiotic resistance genes (ARGs) in the environment. However, the difference of antibiotic residues and ARG profiles in layer and broiler manure as well as their compost remains unexplored. In this study, we investigated the profiles of twelve antibiotics, seventeen ARGs, and class 1 integrase gene (intI1) in layer and broiler manure, and the corresponding compost at large-scale. Compared with layer manure, broiler manure exhibited approximately six times more residual tetracyclines, especially chlortetracycline. The relative abundances of qnrS and ermA genes in broiler manure were significantly higher than those in layer manure. The concentration of tetracyclines not only had a significantly positive correlation with tetracycline resistance genes (tetA and tetC) but was also positively correlated with quinolone resistance (qepA, qnrB, and qnrS) and macrolide resistance (ermA and ermT). Most ARGs in manure were reduced after composting. However, the relative abundance of sulfonamide resistance gene sul1 increased up to 2.41% after composting, which was significantly higher than that of broiler (0.41%) and layer (0.62%) manure. The associated bacterial community was characterized by high-throughput 16S rRNA gene sequencing. The relative abundances of thermophilic bacteria had significant positive correlations with the abundance of sul1 in compost. The composting has a significant impact on the ARG-associated gut microbes in poultry manure. Variation partitioning analysis indicated that the change of bacterial community compositions and antibiotics contributed partially to the shift in ARG profiles. The results indicate that at industry-scale production broiler manure had more antibiotics and ARGs than layer manure did, and composting decreased most ARG abundances in poultry manure except for sulfonamide resistance genes.