Abundance and Diversity of <Emphasis Type="Italic">n</Emphasis>-Alkane-Degrading Bacteria in a Forest Soil Co-Contaminated with Hydrocarbons and Metals: A Molecular Study on <Emphasis Type="Italic">alkB</Emphasis> Homologous Genes

Unraveling functional genes related to biodegradation of organic compounds has profoundly improved our understanding of biological remediation processes, yet the ecology of such genes is only poorly understood. We used a culture-independent approach to assess the abundance and diversity of bacteria catalyzing the degradation of n-alkanes with a chain length between C₅ and C₁₆ at a forest site co-contaminated with mineral oil hydrocarbons and metals for nearly 60 years. The alkB gene coding for a rubredoxin-dependent alkane monooxygenase enzyme involved in the initial activation step of aerobic aliphatic hydrocarbon metabolism was used as biomarker. Within the area of study, four different zones were evaluated: one highly contaminated, two intermediately contaminated, and a noncontaminated zone. Contaminant concentrations, hydrocarbon profiles, and soil microbial respiration and biomass were studied. Abundance of n-alkane-degrading bacteria was quantified via real-time PCR of alkB, whereas genetic diversity was examined using molecular fingerprints (T-RFLP) and clone libraries. Along the contamination plume, hydrocarbon profiles and increased respiration rates suggested on-going natural attenuation at the site. Gene copy numbers of alkB were similar in contaminated and control areas. However, T-RFLP-based fingerprints suggested lower diversity and evenness of the n-alkane-degrading bacterial community in the highly contaminated zone compared to the other areas; both diversity and evenness were negatively correlated with metal and hydrocarbon concentrations. Phylogenetic analysis of alkB denoted a shift of the hydrocarbon-degrading bacterial community from Gram-positive bacteria in the control zone (most similar to Mycobacterium and Nocardia types) to Gram-negative genotypes in the contaminated zones (Acinetobacter and alkB sequences with little similarity to those of known bacteria). Our results underscore a qualitative rather than a quantitative response of hydrocarbon-degrading bacteria to the contamination at the molecular level.     

Salinity controls soil microbial community structure and function in coastal estuarine wetlands

Soil salinity acts as a critical environmental filter on microbial communities, but the consequences for microbial diversity and biogeochemical processes are poorly understood. Here, we characterized soil bacterial communities and microbial functional genes in a coastal estuarine wetland ecosystem across a gradient (~5 km) ranging from oligohaline to hypersaline habitats by applying the PCR-amplified 16S rRNA (rRNA) genes sequencing and microarray-based GeoChip 5.0 respectively. Results showed that saline soils in marine intertidal and supratidal zone exhibited higher bacterial richness and Faith's phylogenetic diversity than that in the freshwater-affected habitats. The relative abundance of taxa assigned to Gammaproteobacteria, Bacteroidetes and Firmicutes was higher with increasing salinity, while those affiliated with Acidobacteria, Chloroflexi and Cyanobacteria were more prevalent in wetland soils with low salinity. The phylogenetic inferences demonstrated the deterministic role of salinity filtering on the bacterial community assembly processes. The abundance of most functional genes involved in carbon degradation and nitrogen cycling correlated negatively with salinity, except for the hzo gene, suggesting a critical role of the anammox process in tidal affected zones. Overall, the salinity filtering effect shapes the soil bacterial community composition, and soil salinity act as a critical inhibitor in the soil biogeochemical processes in estuary ecosystems.     

Pb和Cd对森林土壤细菌功能多样性及群落结构的影响

重金属的毒性系数（The Toxic Factor,TF）是评价重金属潜在生态风险指数（potential ecological risk index,RI）的关键参数。为了探究基于Hakanson提出的TF值是否适用于重金属对土壤微生物的生态风险评估,以TF值为5和30的铅（Pb）和镉（Cd）构建土壤微宇宙试验,构建不同的RI水平（100、200和400）,通过Biolog-ECO板和高通量测序技术分析了Pb和Cd分别对细菌功能多样性及群落结构的影响。结果表明,对照处理（CK）的细菌丰度、功能多样性（Shannon指数,Simpson指数和McIntosh指数）和基因多样性（ACE和Chao1指数）均大于Pb、Cd污染的土壤,随着RI水平的升高,Pb和Cd污染土壤中细菌的丰度、功能多样性（Shannon指数和McIntosh指数）和基因多样性（Chao1指数和ACE指数）呈下降趋势。相同RI水平下,Pb污染土壤中细菌群落的丰度、平均颜色变化率（AWCD）、功能多样性指数、OTUs数和基因多样性指数均显著大于Cd污染（P<0.05）;6大类碳源利用率及主成分（PCA）分析表明,Pb污染土壤中细菌对糖类和羧酸的利用率均显著大于Cd污染（P<0.05）,在不同RI水平和重金属比例下,碳源利用模式而有所不同。同一RI水平下,相对于Pb污染,Cd污染土壤中变形菌门的相对丰度较为丰富,而绿弯菌门的相对丰度稀少;Pb和Cd污染土壤中慢生根瘤菌属、鞘脂单胞菌属、链霉菌属和norank_f__Roseiflexaceae等不同属细菌相对丰度表现出差异性。上述结果表明Hakanson提出的TF值并不适用于评估重金属Pb和Cd对土壤微生物的潜在生态风险。     

青藏高原极端生境细菌多样性差异及影响因素

土壤微生物组对于生态系统的可持续性至关重要,青藏高原独特的地理环境孕育了多样的极端环境,其土壤细菌组成差异及其驱动因素尚不清楚。【目的】探究不同极端生境土壤细菌多样性及其影响因素。【方法】对7种典型的青藏高原极端生境土壤DNA进行16SrRNA基因高通量测序,通过生物信息分析,找出不同生境细菌群落组成、功能差异;结合土壤理化因子,进一步分析细菌组成差异的潜在影响因素。【结果】通过高通量测序,从7个不同生境的36个土壤样品中共获得16 323 712高质量reads,26 504个可操作分类单元(operational taxonomic units, OTUs)。在门分类水平上,各生境中注释到的放线菌门(Actinomycetota)与假单胞菌门(Pseudomonadota)相对丰度均最高;在属分类水平上,芽孢杆菌属(Bacillus)、Ambiguous＿taxa、土壤红杆菌属(Solirubrobacter)、假节杆菌属(Pseudarthrobacter)等为优势属。另外,不同生境中的细菌α多样性无显著差异,但是β多样性差异显著,并且通过LEfSe分析进一步说明了不同生境细菌群...     

土壤含水量驱动土壤病毒和细菌多度及其与土壤异养呼吸关系的变化

土壤微生物是维持陆地生态系统稳定性和功能的重要组成部分。病毒是地球上数量最多的生物实体,也是若干类型生境中微生物数量的重要调节者。因此,了解病毒与微生物的相互作用,对深入认识包括碳循环在内的生态系统过程具有重要意义。在实验室建立土壤微宇宙实验系统,跟踪调查恒定低含水量、恒定高含水量和波动含水量3种水分处理下土壤病毒和细菌多度的变化,以及土壤异养呼吸速率对土壤病毒-细菌相互作用的响应。相较于低水分处理,高水分处理显著增加了病毒多度（P<0.001）和病毒-细菌多度比（P=0.0026）,波动水分处理显著增加了病毒多度（P<0.001）。在高水分处理的土壤微宇宙中,细菌和病毒多度呈现出随时间动荡的信号,即细菌多度表现出增加-降低-增加的趋势,而病毒多度则表现出增加-降低的趋势,且其变化滞后于细菌。土壤异养呼吸速率与土壤含水量（P<0.001）、细菌多度（P=0.0045）和病毒多度（P<0.001）都具有显著的正相关关系。这些结果说明：病毒导致的下行控制可能是细菌多度的重要影响因子,在水分增加情形下,病毒有可能通过加速细菌的更新速率进而加速土壤呼吸。因此,病毒与细菌的相互作用可能是碳循环的重要决定因素。     

Profiling of biodegradation and bacterial 16S rRNA genes in diverse contaminated ecosystems using 60-mer oligonucleotide microarray

We have developed an oligonucleotide microarray for the detection of biodegradative genes and bacterial diversity and tested it in five contaminated ecosystems. The array has 60-mer oligonucleotide probes comprising 14,327 unique probes derived from 1,057 biodegradative genes and 880 probes representing 110 phylogenetic genes from diverse bacterial communities, and we named it as BiodegPhyloChip. The biodegradative genes are involved in the transformation of 133 chemical pollutants. Validation of the microarray for its sensitivity specificity and quantitation were performed using DNA isolated from well-characterized mixed bacterial cultures also having non-target strains, pure degrader strains, and environmental DNA. Application of the developed array using DNA extracted from five different contaminated sites led to the detection of 186 genes, including 26 genes unique to the individual sites. Hybridization of 16S rRNA probes revealed the presence of bacteria similar to well-characterized genera involved in biodegradation of various pollutants. Genes involved in complete degradation pathways for hexachlorocyclohexane (lin), 1,2,4-trichlorobenzene (tcb), naphthalene (nah), phenol (mph), biphenyl (bph), benzene (ben), toluene (tbm), xylene (xyl), phthalate (pht), Salicylate (sal), and resistance to mercury (mer) were detected with highest intensity. The most abundant genes belonged to the enzyme hydroxylases, monooxygenases, and dehydrogenases which were present in all the five samples. Thus, the array developed and validated here shall be useful in assessing not only the biodegradative potential but also the composition of environmentally useful bacteria, simultaneously, from hazardous ecosystems.     

Comparison of Parental and Transgenic Alfalfa Rhizosphere Bacterial Communities Using Biolog GN Metabolic Fingerprinting and Enterobacterial Repetitive Intergenic Consensus Sequence-PCR (ERIC-PCR)

Abstract Rhizosphere bacterial communities of parental and two transgenic alfalfa (Medicago sativa L.) of isogenic background were compared based on metabolic fingerprinting using Biolog GN microplates and DNA fingerprinting of bacterial communities present in Biolog GN substrate wells by enterobacterial repetitive intergenic consensus sequence-PCR (ERIC-PCR). The two transgenic alfalfa expressed either bacterial (Bacillus licheniformis) genes for alpha-amylase or fungal (Phanerochaete chrysosporium) genes for Mn-dependent lignin peroxidase (Austin S, Bingham ET, Matthews DE, Shahan MN, Will J, Burgess RR, Euphytica 85:381–393). Cluster analysis and principal components analysis (PCA) of the Biolog GN metabolic fingerprints indicated consistent differences in substrate utilization between the parental and lignin peroxidase transgenic alfalfa rhizosphere bacterial communities. Cluster analysis of ERIC-PCR fingerprints of the bacterial communities in Biolog GN substrate wells revealed consistent differences in the types of bacteria (substrate-specific populations) enriched from the rhizospheres of each alfalfa genotype. Comparison of ERIC-PCR fingerprints of bacterial strains obtained from substrate wells to substrate community ERIC-PCR fingerprints suggested that a limited number of populations were responsible for substrate oxidation in these wells. Results of this study suggest that transgenic plant genotype may affect rhizosphere microorganisms and that the methodology used in this study may prove a useful approach for the comparison of bacterial communities. Received: 1 June 1998; Accepted: 20 October 1998     

历史因素对土壤微生物群落与外来细菌入侵间关系的影响

群落的组成和结构如何影响其可入侵性一直是入侵生态学的研究热点。然而关于群落可入侵性和群落特征间关系的认知却很不统一。采用交叉互换的试验方法,首先将野外采集的两种长期不同施肥土壤(有机肥和化肥)进行灭菌并回接已方和对方的土壤悬液,研究土壤环境(历史非生物因素)和土壤微生物群落(历史生物因素)对重建土壤微生物群落特征的相对贡献。随后将用红色荧光蛋白标记的青枯菌作为外来种接入重建的土壤中,探究不同土壤微生物群落特征对外来细菌存活数量(前期入侵潜力)和存活时间(后期入侵潜力)的影响。结果表明,历史生物因素对重建土壤的原生动物数量、革兰氏阴性与阳性细菌比等群落特征和外来细菌的存活数量有影响;历史非生物因素对土壤微生物活性、细菌物种多样性和功能多样性等群落特征以及外来细菌入侵土壤后总的存活时间有影响;外来细菌入侵前期状况仅与原生动物数量、革兰氏阴性与阳性细菌比相关,而入侵后期的状况则仅与微生物活性、细菌物种多样性和功能多样性相关。总之,外来细菌在土壤中各时期的入侵潜力和土著微生物群落特征的相关性主要取决于二者是否由同种历史影响因素控制。本研究对于阐明生物群落结构与群落可入侵性之间关系,及指导土壤外来病原菌的防控均具有重要意义。     

Abundance and Activity of 16S rRNA,AmoA and NifH Bacterial Genes During Assisted Phytostabilization of Mine Tailings

Mine tailings in semiarid regions are highly susceptible to erosion and are sources of dust pollution and potential avenues of human exposure to toxic metals. One constraint to revegetation of tailings by phytostabilization is the absence of microbial communities critical for biogeochemical cycling of plant nutrients. The objective of this study was to evaluate specific genes as in situ indicators of biological soil response during phytoremediation. The abundance and activity of 16S rRNA, nifH, and amoA were monitored during a nine month phytostabilization study using buffalo grass and quailbush grown in compost-amended, metalliferous tailings. The compost amendment provided a greater than 5-log increase in bacterial abundance, and survival of this compost-inoculum was more stable in planted treatments. Despite increased abundance, the activity of the introduced community was low, and significant increases were not detected until six and nine months in quailbush, and unplanted compost and buffalo grass treatments, respectively. In addition, increased abundances of nitrogen-fixation (nifH) and ammonia-oxidizing (amoA) genes were observed in rhizospheres of buffalo grass and quailbush, respectively. Thus, plant establishment facilitated the short term stabilization of introduced bacterial biomass and supported the growth of two key nitrogen-cycling populations in compost-amended tailings.     

Cypris Habitat Selection Facilitated by Microbial Films Influences the Vertical Distribution of Subtidal Barnacle Balanus trigonus

The potential driving force(s) of the vertical distribution of subtidal barnacle Balanus trigonus Darwin were investigated using both field and laboratory experiments. Early juveniles (∼24 h old) placed in intertidal [∼0.5 m above mean low water level (MLWL)] and subtidal (∼3 m below MLWL) habitats survived equally well, indicating that the intertidal absence of B. trigonus in Hong Kong waters was not determined by differential mortality. However, enhanced attachment of cyprids in subtidal habitats indicated the importance of differential larval choice in determining their vertical distribution. In the laboratory, cyprids preferred to attach in response to subtidal microbial films, which may implicate microbial films as a primary cue in driving the adult vertical distribution. Microbial films developed in these two habitats differed in their biomass (=total organic carbon), abundance of bacteria and diatoms (determined by fluorescence microscopy), and bacterial diversity (determined by DNA fingerprinting analysis). For example, 6-day films in subtidal habitat had a significantly higher biomass than in films from intertidal habitat (P<0.05). There was no difference in the biomass of films from these two habitats in 9-day films (P>0.05); however, bacterial abundance was greater in subtidal films than in intertidal films, irrespective of the age of the film, although there was no difference in diatom abundance in films from these two habitats. Neither the abundance of bacteria and diatoms nor the biomass correlated with the attachment preferences of cyprids. This study has not provided any data to prove the existence of inductive and inhibitive (to cyprid attachment) bacterial species in subtidal and intertidal films, respectively; however, results indicate that bacterial community provided qualitative information that might explain the preferential attachment of B. trigonus cyprids in subtidal habitat.     

Factors controlling the population dynamics of the clonal helophyte Ranunculus lingua

Abstract. Two marginal and two central populations of the pseudo-annual aquatic plant Ranunculus lingua were studied over four years. The main purpose was to quantify potentially influential abiotic and biotic factors and to derive predictions about life-history differences between the populations. Variation in abundance and height of R. lingua ramets at different depths were related to water-level fluctuations, to abundance of other helophyes (emergent macrophytes), and to the occurrence of invertebrate grazing and fungal pathogens. Clear differences between marginal and central populations were shown in the depth distribution of ramet numbers and ramet heights, as well as in the dynamic patterns, where marginal populations had a higher flux of ramets. These patterns and regression analyses indicated that abiotic factors have a greater influence in marginal populations, whereas biotic factors are more important in central populations. It is suggested that marginal habitats for R. lingua would favour life-histories with a high reproductive capacity, whereas a large size of ramet would be the most important life-history feature in central habitats. This was supported by the fact that ramets in marginal populations, in spite of their smaller size, produced higher number of rhizomes than ramets in central populations. Variation in regional abundance was finally related to differences in demographic processes and dispersal potential between the populations.     

Occurrence and microbial degradation of fipronil residues in tropical highland rhizosphere soils of Kerala,India

The aim of the current study was to analyze the abundance and activity of soil microflora in response to fipronil residues, as well as conjointly to isolate and identify bacteria for the bioremediation of fipronil contaminated soils in the cardamom plantations of Idukki district, Kerala. Soil samples collected from rhizosphere areas of six completely different cardamom plantations were analyzed for fipronil residues, physicochemical properties, biochemical properties, and microbial abundance. Biodegradation studies using isolated bacteria were done both in liquid medium and in soil microcosm fortified with fipronil. Fipronil residues were detected in all sampling sites. Canonical correlation analysis revealed that the influence of fipronil on soil physicochemical properties was more pronounced than that on soil microbial properties. The presence of fipronil residues in the soil did not adversely affect bacterial abundance and activity. Two bacterial strains Staphylococcus arlettae and Bacillus thuringiensis could degrade fipronil in both liquid culture and soil. Paired sample T-test and degradation kinetic study recorded that the bacterial strain S. arlettae was more efficient (81.94%) in fipronil degradation than B. thuringiensis (65.98%). The results revealed the potential for in situ bioremediation of fipronil contaminated soil by bioaugmentation using efficient bacterial isolates.     

Diversity of 16S rRNA and dioxygenase genes detected in coal‐tar‐contaminated site undergoing active bioremediation

Aims: In order to develop effective bioremediation strategies for polyaromatic hydrocarbons (PAHs) degradation, the composition and metabolic potential of microbial communities need to be better understood, especially in highly PAH contaminated sites in which little information on the cultivation‐independent communities is available. Methods and Results: Coal‐tar‐contaminated soil was collected, which consisted of 122·5 mg g^?1 total extractable PAH compounds. Biodegradation studies with this soil indicated the presence of microbial community that is capable of degrading the model PAH compounds viz naphthalene, phenanthrene and pyrene at 50 ppm each. PCR clone libraries were established from the DNA of the coal‐tar‐contaminated soil, targeting the 16S rRNA to characterize (i) the microbial communities, (ii) partial gene fragment encoding the Rieske iron sulfur center (α‐subunit) common to all PAH dioxygenase enzymes and (iii) β‐subunit of dioxygenase. Phylotypes related to Proteobacteria (Alpha‐, Epsilon‐ and Gammaproteobacteria), Acidobacteria, Actinobacteria, Firmicutes, Gemmatimonadetes and Deinococci were detected in 16S rRNA derived clone libraries. Many of the gene fragment sequences of α‐subunit and β‐subunit of dioxygenase obtained from the respective clone libraries fell into clades that are distinct from the reference dioxygenase gene sequences. Presence of consensus sequence of the Rieske type [2Fe‐2S] cluster binding site suggested that these gene fragments encode for α‐subunit of dioxygenase gene. Conclusions: Sequencing of the cloned libraries representing α‐subunit gene fragments (Rf1) and β‐subunit of dioxygenase showed the presence of hitherto unidentified dioxygenase in coal‐tar‐contaminated soil. Significance and Impact of the Study: The combination of the Rieske primers and bacterial community profiling represents a powerful tool for both assessing bioremediation potential and the exploration of novel dioxygenase genes in a contaminated environment.     

The influence of stage-dependent dispersal on the population dynamics of three amphipod species

In metapopulations, the maintenance of local populations can depend on source–sink dynamics, where populations with positive growth rate seed populations with negative growth rate. The pattern and probability of successful dispersal among habitats can therefore be crucial in determining whether local populations will become rare or increase in abundance. We present here data on the dispersal strategy and population dynamics of three marine amphipods living in pen shells (Atrina rigida) in the Gulf of Mexico. The three amphipod species in this study disperse at different life stages. Neomegamphopus hiatus and Melita nitida disperse as adults, while Bemlos unicornis disperses as juveniles. The two species that disperse as adults have the highest initial population sizes when a new shell becomes available, likely caused by the arriving females releasing their brood into these recently occupied shells. This dispersal pattern results in initially higher population growth, but fewer occupied shells, as noted by their clumped distribution. In contrast, the species that disperses as juveniles accumulates more slowly and more evenly across habitats, eventually dominating the other two in terms of numerical abundance. The metapopulation dynamics of the three species seems to be highly dependent on the life history stage involved in dispersal. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">Escherichia coli ydiO</Emphasis> and <Emphasis Type="Italic">ydiQRST</Emphasis> genes encode components of acyl-CoA dehydrogenase complex of anaerobic fatty acid β-oxidation pathway

Escherichia coli open reading frames ydiO and ydiQRST were identified as genes encoding components of the acyl-CoA dehydrogenase complex of anaerobic fatty acid β-oxidation. Individual or concomitant inactivation of fadE gene, encoding known aerobic acyl-CoA dehydrogenase, and ydiO and/or ydiQRST genes did not affect cellular growth on glucose as a sole carbon source. Aerobic growth on sodium oleate was observed only for the cells with intact fadE gene. With an alternative electron acceptor, the cells possessing intact fadE gene demonstrated anaerobic growth on sodium oleate irrespective of the presence or absence of ydiO and ydiQRST genes. For the fadE-deficient mutants, anaerobic growth on sodium oleate was observed only for cells with intact ydiO and ydiQRST genes, while the fadE/ydiO and fadE/ydiQRST mutants failed to grow under the similar conditions.     

Contrasting effects of ultraviolet radiation on the growth efficiency of freshwater bacteria

In this study, we tested the hypothesis that the growth efficiency of freshwater bacteria is differentially affected by ultraviolet radiation (UVR, 280–400 nm) as mediated through changes in their production and respiration rates. Five bacterial strains affiliated to Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Actinobacteria were isolated from different freshwater habitats and exposed in the laboratory to photosynthetically active radiation (PAR) and PAR + UVR, or kept in the dark for 4 h. Afterward, bacterial carbon production and respiration were assessed by measuring leucine incorporation and oxygen consumption rates, respectively. Ultraviolet radiation decreased significantly the bacterial production of Acidovorax sp., Pseudomonas sp. and Actinobacterium MHWTa3, and the respiration rate of Acidovorax sp. and Acinetobacter lwoffii. Measurements of respiration of a natural bacterial community collected from the same lake where A. lwoffii was isolated resulted in significantly higher rates after exposure to PAR + UVR than in the dark. In the presence of UVR, bacterial growth efficiency significantly decreased in Acidovorax sp., Pseudomonas sp., and Actinobacterium MHWTa3, but it increased in A. lwoffii or it remained unchanged in Sphingomonas sp. Our results indicate that although the outcome was strain-specific, UVR has the potential to alter the efficiency by which dissolved organic matter is transformed into bacterial biomass and thus to affect the biogeochemical carbon cycle.     

锡林河流域潜在不产氧光合细菌陆向分异特征及影响因素

【目的】为探明锡林河流域潜在不产氧光合细菌（anoxygenic photosynthetic bacteria,AnPB）的陆向分异特征及影响因素。【方法】本研究沿着陆向梯度依次采集水生湍流带、缓流带、滞流带、水偏湿生样带、湿偏旱生样带、旱生样带土壤样品。基于文献建立AnPB在科水平的数据库,运用16S rRNA基因高通量测序筛选科水平潜在AnPB类群及其组成丰度的陆向分异,运用皮尔逊相关性及冗余分析等研究土壤理化因子对潜在AnPB陆向分异的影响。【结果】紫色硫细菌（外硫红螺菌科）和紫色非硫细菌（红杆菌科、红环菌科、醋酸杆菌科、丛毛单胞菌科、全噬菌科）主要分布在水生及水偏湿生生境,其相对丰度与湿度呈显著（P<0.05）或极显著（P<0.01）正相关关系;紫色非硫细菌（红螺菌科、慢生根瘤菌科、生丝微菌科、红菌科）、芽单胞菌科、酸杆菌科、绿色非硫细菌（蔷薇菌科）等主要分布在湿偏旱生和旱生环境中,其相对丰度与盐度和全氮含量呈显著（P<0.05）或极显著（P<0.01）正相关关系;多元回归树分析显示,盐度、湿度、全氮对潜在AnPB陆向分异的总解释度分别为62.39%、...     

Species Composition of Bacterial Communities Influences Attraction of Mosquitoes to Experimental Plant Infusions

In the container habitats of immature mosquitoes, catabolism of plant matter and other organic detritus by microbial organisms produces metabolites that mediate the oviposition behavior of Aedes aegypti and Aedes albopictus. Public health agencies commonly use oviposition traps containing plant infusions for monitoring populations of these mosquito species, which are global vectors of dengue viruses. In laboratory experiments, gravid females exhibited significantly diminished responses to experimental infusions made with sterilized white oak leaves, showing that attractive odorants were produced through microbial metabolic activity. We evaluated effects of infusion concentration and fermentation time on attraction of gravid females to infusions made from senescent bamboo or white oak leaves. We used plate counts of heterotrophic bacteria, total counts of 4′,6-diamidino-2-phenylindole-stained bacterial cells, and 16S ribosomal DNA (rDNA) polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) to show that changes in the relative abundance of bacteria and the species composition of bacterial communities influenced attraction of gravid A. aegypti and A. albopictus mosquitoes to infusions. DGGE profiles showed that bacterial species composition in infusions changed over time. Principal components analysis indicated that oviposition responses to plant infusions were in general most affected by bacterial diversity and abundance. Analysis of bacterial 16S rDNA sequences derived from DGGE bands revealed that Proteobacteria (Alpha-, Beta-, Delta-, and Gamma-) were the predominant bacteria detected in both types of plant infusions. Gravid A. aegypti were significantly attracted to a mix of 14 bacterial species cultured from bamboo leaf infusion. The oviposition response of gravid mosquitoes to plant infusions is strongly influenced by abundance and diversity of bacterial species, which in turn is affected by plant species, leaf biomass, and fermentation time.     

Amplicon-based profiling of bacteria in raw and secondary treated wastewater from treatment plants across Australia

In this study, we investigated the use of Illumina high-throughput sequencing of 16S ribosomal RNA (rRNA) amplicons to explore microbial diversity and community structure in raw and secondary treated wastewater (WW) samples from four municipal wastewater treatment plants (WWTPs A–D) across Australia. Sequence reads were analyzed to determine the abundance and diversity of bacterial communities in raw and secondary treated WW samples across the four WWTPs. In addition, sequence reads were also characterized to phenotypic features and to estimate the abundance of potential pathogenic bacterial genera and antibiotic-resistant genes in total bacterial communities. The mean coverage, Shannon diversity index, observed richness (S _obs), and abundance-based coverage estimate (ACE) of richness for raw and secondary treated WW samples did not differ significantly (P > 0.05) among the four WWTPs examined. Generally, raw and secondary treated WW samples were dominated by members of the genera Pseudomonas, Arcobacter, and Bacteroides. Evaluation of source contributions to secondary treated WW, done using SourceTracker, revealed that 8.80–61.4% of the bacterial communities in secondary treated WW samples were attributed to raw WW. Twenty-five bacterial genera were classified as containing potential bacterial pathogens. The abundance of potentially pathogenic genera in raw WW samples was higher than that found in secondary treated WW samples. Among the pathogenic genera identified, Pseudomonas and Arcobacter had the greatest percentage of the sequence reads. The abundances of antibiotic resistance genes were generally low (<0.5%), except for genes encoding ABC transporters, which accounted for approximately 3% of inferred genes. These findings provided a comprehensive profile of bacterial communities, including potential bacterial pathogens and antibiotic-resistant genes, in raw and secondary treated WW samples from four WWTPs across Australia and demonstrated that Illumina high-throughput sequencing can be an alternative approach for monitoring WW quality in order to protect environmental and human health.