Microbial Distribution Patterns Research Articles

Impacts of environmental factors on microbial diversity, distribution patterns and syntrophic correlation in anaerobic processes.

Anaerobic processes are widely used for treating high-strength organic wastewater. Understanding the ecological patterns of the microorganisms involved and the effect of environmental factors on microbial community are important to manage the performance of anaerobic processes. Microbial communities of 12 anaerobic sludge samples acclimated under different environmental conditions were investigated. Genera detected from these anaerobic sludge samples generally presented three distribution patterns: frequently detected with high abundance, frequently detected with low abundance and occasionally detected with permanently low abundance. The type of feed stock was one of the most important process parameters affecting the shape of microbial community (e.g., Syntrophus, Methylomonas and Methylobacillus). Dye wastewater (Bacteroides) and the supplement of conductive materials (genus T78) were also found to shape the microbial community. Some syntrophic bacteria and methanogens were rare in many anaerobic samples. However, correlation analysis suggested that rare genera are potential syntrophic partners and are responsible for syntrophic methanogenesis.

Small-Scale Soil Microbial Community Heterogeneity Linked to Landform Historical Events on King George Island, Maritime Antarctica.

Although research on microbial biogeography has made great progress in the past decade, distributions of terrestrial microbial communities in extreme environments such as Antarctica are not well understood. In addition, knowledge of whether and how historical contingencies affect microbial distributions at small spatial scales is lacking. Here, we analyzed soil-borne microbial (bacterial, archaeal, and fungal) communities in 12 quadrat plots around the Fildes Region of King George Island, maritime Antarctica, and the communities were divided into two groups according to the soil elemental compositions and environmental attributes of Holocene raised beach and Tertiary volcanic stratigraphy. Prokaryotic communities of the two groups were well separated; the prokaryotic data were primarily correlated with soil elemental compositions and were secondly correlated with environmental attributes (e.g., soil pH, total organic carbon, NO3-, and vegetation coverage; Pearson test, r = 0.59 vs. 0.52, both P < 0.01). The relatively high abundance of P, S, Cl, and Br in Group 1 (Holocene raised beach site) was likely due to landform uplift. Lithophile-elements (Si, Al, Ca, Sr, Ti, V, and Fe) correlated with prokaryotic communities in Group 2 may have originated from weathering of Tertiary volcanic rock. No significant correlations were found between the fungal community distribution and both the soil elemental composition and environmental attributes in this study; however, Monte Carlo tests revealed that elements Sr and Ti, soil pH, sampling altitude, and moss and lichen species numbers had significant impacts on fungal communities. The elements and nutrients accumulated during the formation of different landforms influenced the development of soils, plant growth, and microbial communities, and this resulted in small-scale spatially heterogeneous biological distributions. These findings provide new evidence that geological evolutionary processes in the Fildes Region were crucial to its microbial community development, and the results highlight that microbial distribution patterns are the legacies of historical events at this small spatial scale. Based on this study, the ice-free regions in maritime Antarctica represent suitable research sites for studying the influence of geomorphological features on microbial distributions, and we envision the possibility of a site-specific landform assignment through the analysis of the soil prokaryotic community structure.

Occurrence of microbial indicators, pathogenic bacteria and viruses in tropical surface waters subject to contrasting land use

Fecal indicator bacteria, such as Escherichia coli (E.coli) and Enterococcus, have been widely used to indicate the presence of pathogens. However, the suitability of fecal indicator bacteria to represent health risks is still being challenged, particularly in tropical aquatic environments. The objective of this study is to understand the occurrence and prevalence of indicators and pathogens in areas with contrasting land use, as well as to identify the major correlations between indicators, pathogens and environmental parameters. The spatial and temporal variation of indicators and pathogens was studied to examine the distribution patterns for areas with different land use, and the impact of seasonal changes on microbial populations. A total of 234 water samples were sampled for two years from reservoirs and their tributaries, and tested for fecal indicator bacteria, coliphages, human specific markers, pathogenic bacteria and viruses. The prevalence of indicators and pathogens in reservoirs were generally low, while relatively high concentrations were observed in tributaries to varying degrees. Of the enteric viruses, norovirus GII was among the most prevalent and had the highest concentration. Although strong correlations were found between indicators, only relatively weak correlations were found between indicators and pathogens. The results in this study showed that none of the bacteria/phage indicators were universal predictors for pathogens. Inclusion of the alternative indicators, Methanobrevibacter smithii, Bacteroides and human polyomaviruses (HPyVs) to monitoring programs could help to determine whether the fecal source was human. The microbial distribution patterns allow the classification of sampling sites to different clusters and thus, help to identify sites which have poor water quality. This approach will be useful for water quality management to pinpoint factors that influence water quality and help to prioritize sites for restoration of water quality.

Macro and Microelements Drive Diversity and Composition of Prokaryotic and Fungal Communities in Hypersaline Sediments and Saline-Alkaline Soils.

Understanding the effects of environmental factors on microbial communities is critical for microbial ecology, but it remains challenging. In this study, we examined the diversity (alpha diversity) and community compositions (beta diversity) of prokaryotes and fungi in hypersaline sediments and salinized soils from northern China. Environmental variables were highly correlated, but they differed significantly between the sediments and saline soils. The compositions of prokaryotic and fungal communities in the hypersaline sediments were different from those in adjacent saline–alkaline soils, indicating a habitat-specific microbial distribution pattern. The macroelements (S, P, K, Mg, and Fe) and Ca were, respectively, correlated closely with the alpha diversity of prokaryotes and fungi, while the macronutrients (e.g., Na, S, P, and Ca) were correlated with the prokaryotic and fungal beta-diversity (P ≤ 0.05). And, the nine microelements (e.g., Al, Ba, Co, Hg, and Mn) and micronutrients (Ba, Cd, and Sr) individually shaped the alpha diversity of prokaryotes and fungi, while the six microelements (e.g., As, Ba, Cr, and Ge) and only the trace elements (Cr and Cu), respectively, influenced the beta diversity of prokaryotes and fungi (P < 0.05). Variation-partitioning analysis (VPA) showed that environmental variables jointly explained 55.49% and 32.27% of the total variation for the prokaryotic and fungal communities, respectively. Together, our findings demonstrate that the diversity and community composition of the prokaryotes and fungi were driven by different macro and microelements in saline habitats, and that geochemical elements could more widely regulate the diversity and community composition of prokaryotes than these of fungi.

Distribution Patterns of Microbial Community Structure Along a 7000-Mile Latitudinal Transect from the Mediterranean Sea Across the Atlantic Ocean to the Brazilian Coastal Sea.

A central goal in marine microecology is to understand the ecological factors shaping spatiotemporal microbial patterns and the underlying processes. We hypothesized that abiotic and/or biotic interactions are probably more important for explaining the distribution patterns of marine bacterioplankton than environmental filtering. In this study, surface seawater samples were collected about 7000miles from the Mediterranean Sea, transecting the North Atlantic Ocean, to the Brazilian marginal sea. In bacterial biosphere, SAR11, SAR86, Rhodobacteraceae, and Rhodospiriaceae were predominant in the Mediterranean Sea; Prochlorococcus was more frequent in Atlantic Ocean; whereas in the Brazilian coastal sea, the main bacterial members were Synechococcus and SAR11. With respect to archaea, Euryarchaeota were predominant in the Atlantic Ocean and Thaumarchaeota in the Mediterranean Sea. With respect to the eukaryotes, Syndiniales, Spumellaria, Cryomonadida, and Chlorodendrales were predominant in the open ocean, while diatoms and microzooplankton were dominant in the coastal sea. Distinct clusters of prokaryotes and eukaryotes displayed clear spatial heterogeneity. Among the environmental parameters measured, temperature and salinity were key factors controlling bacterial and archaeal community structure, respectively, whereas N/P/Si contributed to eukaryotic variation. The relative contribution of environmental parameters to the microbial distribution pattern was 45.2%. Interaction analysis showed that Gammaproteobacteria, Alphaproteobacteria, and Flavobacteriia were the keystone taxa within the positive-correlation network, while Thermoplasmata was the main contributor in the negative-correlation network. Our study demonstrated that microbial communities are co-governed by environmental filtering and biotic interactions, which are the main deterministic driving factors modulating the spatiotemporal patterns of marine plankton synergistically at the regional or global levels.

Polyhydroxyalkanoates (PHA) production by photoheterotrophic microbial consortia: Effect of culture conditions over microbial population and biopolymer yield and composition

Three microbial consortia (C2, C4, C5) grown under photoheterotrophic conditions assimilated acetate and butyrate, as individual and mixed substrates. By controlling the culture conditions, it was possible to manipulate the microbial population composition and thus the yield of polyhydroxyalkanoates (PHA) accumulation. Under limited ammonium conditions, pH control, and a sequential two-step process, C2 and C4 produced PHA. C4 showed the highest production of 44% of the cell dry mass (CDM), close to the theoretical value calculated with a stoichiometric balance. Analysis of the confocal microscopy images confirmed the accumulated biopolymer percentages produced by each consortium, and it was in close correlation with microbial distribution and substrate consumption pattern. 1H, 13C, NMR, and MALDI-TOF spectra identified the primary structure of the obtained biopolymers as copolymers of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV). This composition allows for better mechanical properties compared to the PHB homopolymer. Microbial characterization showed a similar microbial population with different proportions for C2 and C4. The highest PHA production in C4 was associated with higher abundances of PHA producers, including Clostridium (29%), Pseudomonas (8%) and Rhodopseudomonas (5%). Both microbial consortia showed that a portion of their microbial populations were able to perform syntrophic reactions (Dysgonomonas and Clostridium).

Analysis of Circulating Immune Complexes and Detection of Microbial Antigenic Components in Breast Tumours in Anambra State Nigeria

Quantitative measurement of circulating immune complexes in cancer patients is a widely accepted measure linking immune complexes as useful for treatment monitoring. However, the components of these immune complexes are generally understudied. By the analysis of immune complexes, this work elicited some microbial agents that could be associated with breast tumours. Total of 99 female subjects were randomly recruited for this study, of which 24 had benign tumour, 25 had malignant tumour and 50 were tumour free controls subjects. The mean age of the female subjects with benign breast tumour was 37.9±10.1 years; malignant 49.6±10.8 and control subjects 35.9±9.0, and they were confirmed free from chemotherapy, autoimmune diseases and HIV infection. Immune complexes were precipitated and dissociated. Characterization of the antigens/antibodies was done using Enzyme linked immunoassay technique. Microbial antigenic components were detected in 21 benign tumour subjects, 20 malignant tumour subjects and 11 control subjects. Homogeneity and heterogeneity patterns of microbial antigenic distribution were seen in different groups. Heterogeneity pattern was prevalent in subjects with tumours. Detection of HCV was significantly high in subjects with benign and malignant tumours, while presence of Plasmodium falciparum, Helicobacter pylori and Salmonella typhi was also prominent. HBV and treponema pallidum were implicated. Heterogeneity pattern was prevalent in late stages of breast cancer while Plasmodium falciparum , HCV and Salmonella typhi were most prominent. The burden of microbial infection is prevalent in breast tumour subjects. Presence of the microbial antigens would represent the burden of the microbial infection in tumour development and the consequences of the persistent circulation of these microbial proteins were discussed.

Microbial functional genes enriched in the Xiangjiang River sediments with heavy metal contamination.

BackgroundXiangjiang River (Hunan, China) has been contaminated with heavy metal for several decades by surrounding factories. However, little is known about the influence of a gradient of heavy metal contamination on the diversity, structure of microbial functional gene in sediment. To deeply understand the impact of heavy metal contamination on microbial community, a comprehensive functional gene array (GeoChip 5.0) has been used to study the functional genes structure, composition, diversity and metabolic potential of microbial community from three heavy metal polluted sites of Xiangjiang River.ResultsA total of 25595 functional genes involved in different biogeochemical processes have been detected in three sites, and different diversities and structures of microbial functional genes were observed. The analysis of gene overlapping, unique genes, and various diversity indices indicated a significant correlation between the level of heavy metal contamination and the functional diversity. Plentiful resistant genes related to various metal were detected, such as copper, arsenic, chromium and mercury. The results indicated a significantly higher abundance of genes involved in metal resistance including sulfate reduction genes (dsr) in studied site with most serious heavy metal contamination, such as cueo, mer, metc, merb, tehb and terc gene. With regard to the relationship between the environmental variables and microbial functional structure, S, Cu, Cd, Hg and Cr were the dominating factor shaping the microbial distribution pattern in three sites.ConclusionsThis study suggests that high level of heavy metal contamination resulted in higher functional diversity and the abundance of metal resistant genes. These variation therefore significantly contribute to the resistance, resilience and stability of the microbial community subjected to the gradient of heavy metals contaminant in Xiangjiang River.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0800-x) contains supplementary material, which is available to authorized users.

Changes in microbial communities associated with gas hydrates in subseafloor sediments from the Nankai Trough.

Little is known about the microbial distribution patterns in subseafloor sediments. This study examines microbial diversity and activities in sediments of the Nankai Trough, where biogenic gas hydrates are deposited. Illumina sequencing of 16S rRNA genes revealed that the prokaryotic community structure is correlated with hydrate occurrence and depth but not with the sedimentary facies. The bacterial phyla 'Atribacteria' lineage JS1 and Chloroflexi dominated in all samples, whereas lower taxonomic units of Chloroflexi accounted for community variation related to hydrate saturation. In archaeal communities, 'Bathyarchaeota' was significantly abundant in the hydrate-containing samples, whereas Marine Benthic Group-B dominated in the upper sediments without hydrates. mcrA gene sequences assigned to deeply branching groups and ANME-1 were detected only in hydrate-containing samples. A predominance of hydrogenotrophic methanogens, Methanomicrobiales and Methanobacteriales, over acetoclastic methanogens was found throughout the depth. Incubation tests on hydrate-containing samples with a stable isotope tracer showed anaerobic methane oxidation activities under both low- and seawater-like salinity conditions. These results indicate that the distribution patterns of microorganisms involved in carbon cycling changed with gas hydrate occurrence, possibly because of the previous hydrate dissociation followed by pore water salinity decrease in situ, as previously proposed by a geochemical study at the study site.

Microbial eukaryotic distributions and diversity patterns in a deep-sea methane seep ecosystem.

Although chemosynthetic ecosystems are known to support diverse assemblages of microorganisms, the ecological and environmental factors that structure microbial eukaryotes (heterotrophic protists and fungi) are poorly characterized. In this study, we examined the geographic, geochemical and ecological factors that influence microbial eukaryotic composition and distribution patterns within Hydrate Ridge, a methane seep ecosystem off the coast of Oregon using a combination of high-throughput 18S rRNA tag sequencing, terminal restriction fragment length polymorphism fingerprinting, and cloning and sequencing of full-length 18S rRNA genes. Microbial eukaryotic composition and diversity varied as a function of substrate (carbonate versus sediment), activity (low activity versus active seep sites), sulfide concentration, and region (North versus South Hydrate Ridge). Sulfide concentration was correlated with changes in microbial eukaryotic composition and richness. This work also revealed the influence of oxygen content in the overlying water column and water depth on microbial eukaryotic composition and diversity, and identified distinct patterns from those previously observed for bacteria, archaea and macrofauna in methane seep ecosystems. Characterizing the structure of microbial eukaryotic communities in response to environmental variability is a key step towards understanding if and how microbial eukaryotes influence seep ecosystem structure and function.

Development of Spatial Distribution Patterns by Biofilm Cells.

Confined spatial patterns of microbial distribution are prevalent in nature, such as in microbial mats, soil communities, and water stream biofilms. The symbiotic two-species consortium of Pseudomonas putida and Acinetobacter sp. strain C6, originally isolated from a creosote-polluted aquifer, has evolved a distinct spatial organization in the laboratory that is characterized by an increased fitness and productivity. In this consortium, P. putida is reliant on microcolonies formed by Acinetobacter sp. C6, to which it attaches. Here we describe the processes that lead to the microcolony pattern by Acinetobacter sp. C6. Ecological spatial pattern analyses revealed that the microcolonies were not entirely randomly distributed and instead were arranged in a uniform pattern. Detailed time-lapse confocal microscopy at the single-cell level demonstrated that the spatial pattern was the result of an intriguing self-organization: small multicellular clusters moved along the surface to fuse with one another to form microcolonies. This active distribution capability was dependent on environmental factors (carbon source and oxygen) and historical contingency (formation of phenotypic variants). The findings of this study are discussed in the context of species distribution patterns observed in macroecology, and we summarize observations about the processes involved in coadaptation between P. putida and Acinetobacter sp. C6. Our results contribute to an understanding of spatial species distribution patterns as they are observed in nature, as well as the ecology of engineered communities that have the potential for enhanced and sustainable bioprocessing capacity.

Contrasting microbial functional genes in two distinct saline-alkali and slightly acidic oil-contaminated sites

To compare the functional gene structure and diversity of microbial communities in saline-alkali and slightly acidic oil-contaminated sites, 40 soil samples were collected from two typical oil exploration sites in North and South China and analyzed with a comprehensive functional gene array (GeoChip 3.0). The overall microbial pattern was significantly different between the two sites, and a more divergent pattern was observed in slightly acidic soils. Response ratio was calculated to compare the microbial functional genes involved in organic contaminant degradation and carbon, nitrogen, phosphorus, and sulfur cycling. The results indicated a significantly low abundance of most genes involved in organic contaminant degradation and in the cycling of nitrogen and phosphorus in saline-alkali soils. By contrast, most carbon degradation genes and all carbon fixation genes had similar abundance at both sites. Based on the relationship between the environmental variables and microbial functional structure, pH was the major factor influencing the microbial distribution pattern in the two sites. This study demonstrated that microbial functional diversity and heterogeneity in oil-contaminated environments can vary significantly in relation to local environmental conditions. The limitation of nitrogen and phosphorus and the low degradation capacity of organic contaminant should be carefully considered, particularly in most oil-exploration sites with saline-alkali soils.

Metabolic Flexibility as a Major Predictor of Spatial Distribution in Microbial Communities

A better understand the ecology of microbes and their role in the global ecosystem could be achieved if traditional ecological theories can be applied to microbes. In ecology organisms are defined as specialists or generalists according to the breadth of their niche. Spatial distribution is often used as a proxy measure of niche breadth; generalists have broad niches and a wide spatial distribution and specialists a narrow niche and spatial distribution. Previous studies suggest that microbial distribution patterns are contrary to this idea; a microbial generalist genus (Desulfobulbus) has a limited spatial distribution while a specialist genus (Methanosaeta) has a cosmopolitan distribution. Therefore, we hypothesise that this counter-intuitive distribution within generalist and specialist microbial genera is a common microbial characteristic. Using molecular fingerprinting the distribution of four microbial genera, two generalists, Desulfobulbus and the methanogenic archaea Methanosarcina, and two specialists, Methanosaeta and the sulfate-reducing bacteria Desulfobacter were analysed in sediment samples from along a UK estuary. Detected genotypes of both generalist genera showed a distinct spatial distribution, significantly correlated with geographic distance between sites. Genotypes of both specialist genera showed no significant differential spatial distribution. These data support the hypothesis that the spatial distribution of specialist and generalist microbes does not match that seen with specialist and generalist large organisms. It may be that generalist microbes, while having a wider potential niche, are constrained, possibly by intrageneric competition, to exploit only a small part of that potential niche while specialists, with far fewer constraints to their niche, are more capable of filling their potential niche more effectively, perhaps by avoiding intrageneric competition. We suggest that these counter-intuitive distribution patterns may be a common feature of microbes in general and represent a distinct microbial principle in ecology, which is a real challenge if we are to develop a truly inclusive ecology.

Microorganisms persist at record depths in the subseafloor of the Canterbury Basin.

The subsurface realm is colonized by microbial communities to depths of >1000 meters below the seafloor (m.b.sf.), but little is known about overall diversity and microbial distribution patterns at the most profound depths. Here we show that not only Bacteria and Archaea but also Eukarya occur at record depths in the subseafloor of the Canterbury Basin. Shifts in microbial community composition along a core of nearly 2 km reflect vertical taxa zonation influenced by sediment depth. Representatives of some microbial taxa were also cultivated using methods mimicking in situ conditions. These results suggest that diverse microorganisms persist down to 1922 m.b.sf. in the seafloor of the Canterbury Basin and extend the previously known depth limits of microbial evidence (i) from 159 to 1740 m.b.sf. for Eukarya and (ii) from 518 to 1922 m.b.sf. for Bacteria.

Aboveground Deadwood Deposition Supports Development of Soil Yeasts

Unicellular saprobic fungi (yeasts) inhabit soils worldwide. Although yeast species typically occupy defined areas on the biome scale, their distribution patterns within a single type of vegetation, such as forests, are more complex. In order to understand factors that shape soil yeast communities, soils collected underneath decaying wood logs and under forest litter were analyzed. We isolated and identified molecularly a total of 25 yeast species, including three new species. Occurrence and distribution of yeasts isolated from these soils provide new insights into ecology and niche specialization of several soil-borne species. Although abundance of typical soil yeast species varied among experimental plots, the analysis of species abundance and community composition revealed a strong influence of wood log deposition and leakage of organic carbon. Unlike soils underneath logs, yeast communities in adjacent areas harbored a considerable number of transient (phylloplane-related) yeasts reaching 30% of the total yeast quantity. We showed that distinguishing autochthonous community members and species transient in soils is essential to estimate appropriate effects of environmental factors on soil fungi. Furthermore, a better understanding of species niches is crucial for analyses of culture-independent data, and may hint to the discovery of unifying patterns of microbial species distribution.

Microbial community structure and activity linked to contrasting biogeochemical gradients in bog and fen environments of the Glacial Lake Agassiz Peatland.

The abundances, compositions, and activities of microbial communities were investigated at bog and fen sites in the Glacial Lake Agassiz Peatland of northwestern Minnesota. These sites contrast in the reactivity of dissolved organic matter (DOM) and the presence or absence of groundwater inputs. Microbial community composition was characterized using pyrosequencing and clone library construction of phylogenetic marker genes. Microbial distribution patterns were linked to pH, concentrations of dissolved organic carbon and nitrogen, C/N ratios, optical properties of DOM, and activities of laccase and peroxidase enzymes. Both bacterial and archaeal richness and rRNA gene abundance were >2 times higher on average in the fen than in the bog, in agreement with a higher pH, labile DOM content, and enhanced enzyme activities in the fen. Fungi were equivalent to an average of 1.4% of total prokaryotes in gene abundance assayed by quantitative PCR. Results revealed statistically distinct spatial patterns between bacterial and fungal communities. Fungal distribution did not covary with pH and DOM optical properties and was vertically stratified, with a prevalence of Ascomycota and Basidiomycota near the surface and much higher representation of Zygomycota in the subsurface. In contrast, bacterial community composition largely varied between environments, with the bog dominated by Acidobacteria (61% of total sequences), while the Firmicutes (52%) dominated in the fen. Acetoclastic Methanosarcinales showed a much higher relative abundance in the bog, in contrast to the dominance of diverse hydrogenotrophic methanogens in the fen. This is the first quantitative and compositional analysis of three microbial domains in peatlands and demonstrates that the microbial abundance, diversity, and activity parallel with the pronounced differences in environmental variables between bog and fen sites.

The microbial diversity of a storm cloud as assessed by hailstones

Being an extreme environment, the atmosphere may act as a selective barrier for bacterial dispersal, where only most robust organisms survive. By remaining viable during atmospheric transport, these cells affect the patterns of microbial distribution and modify the chemical composition of the atmosphere. The species evenness and richness, and the community composition of a storm cloud were studied applying cultivation-dependent and cultivation-independent techniques to a collection of hailstones. In toto 231 OTUs were identified, and the total species richness was estimated to be about 1800 OTUs. The diversity indices - species richness and evenness - suggest a functionally stable community, capable of resisting environmental stress. A broad substrate spectrum of the isolates with epiphytic origin (genus Methylobacterium) implied opportunistic ecologic strategy with high growth rates and fast growth responses. These may grow in situ despite their short residence times in cloud droplets. In addition, epiphytic isolates utilized many atmospheric organic compounds, including a variety of carboxylic acids. In summary, the highly diverse bacterial community, within which the opportunistic bacteria may be particularly important in terms of atmospheric chemistry, is likely to remain functional under stressful conditions. Overall our study adds important details to the growing evidence of active microbial life in clouds.

Spatial scaling of arbuscular mycorrhizal fungal diversity is affected by farming practice

Evidence suggests that microbial communities show patterns of spatial scaling which can be driven by geographical distance and environmental heterogeneity. Here we demonstrate that human management can have a major impact on microbial distribution patterns at both the local and landscape scale. Mycorrhizal fungi are vital components of terrestrial ecosystems, forming a mutualistic symbiosis with plant roots which has a major impact on above ground ecology and productivity. We used contrasting agricultural systems to investigate the spatial scaling of the most widespread mycorrhizal fungus group, the arbuscular mycorrhizal fungi (AMF). Using multiple sampling sites with a maximum separation of 250 km we describe for the first time the roles which land management, environmental heterogeneity and geographical distance play in determining spatial patterns of microbial distribution. Analysis of AMF taxa-area relationships at each sampling site revealed that AMF diversity and spatial turnover was greater under organic relative to conventional farm management. At the regional scale (250 km) distance-decay analyses showed that there was significant change in AMF community composition with distance, and that this was greater under organic relative to conventional management. Environmental heterogeneity was found to be the major factor determining turnover of AMF taxa at the landscape scale. Overall we demonstrate that human management can play a key role in determining the turnover of microbial communities at both the local and regional scales.

Complex phylogeographic patterns in the freshwater alga Synura provide new insights into ubiquity vs. endemism in microbial eukaryotes.

The global distribution, abundance, and diversity of microscopic freshwater algae demonstrate an ability to overcome significant barriers such as dry land and oceans by exploiting a range of biotic and abiotic colonization vectors. If these vectors are considered unlimited and colonization occurs in proportion to population size, then globally ubiquitous distributions are predicted to arise. This model contrasts with observations that many freshwater microalgal taxa possess true biogeographies. Here, using a concatenated multigene data set, we study the phylogeography of the freshwater heterokont alga Synura petersenii sensu lato. Our results suggest that this Synura morphotaxon contains both cosmopolitan and regionally endemic cryptic species, co-occurring in some cases, and masked by a common ultrastructural morphology. Phylogenies based on both proteins (seven protein-coding plastid and mitochondrial genes) and DNA (nine genes including ITS and 18S rDNA) reveal pronounced biogeographic delineations within phylotypes of this cryptic species complex while retaining one clade that is globally distributed. Relaxed molecular clock calculations, constrained by fossil records, suggest that the genus Synura is considerably older than currently proposed. The availability of tectonically relevant geological time (10⁷-10⁸ years) has enabled the development of the observed, complex biogeographic patterns. Our comprehensive analysis of freshwater algal biogeography suggests that neither ubiquity nor endemism wholly explains global patterns of microbial eukaryote distribution and that processes of dispersal remain poorly understood.

Histomicrobiologic aspects of the root canal system and periapical lesions in dogs' teeth after rotary instrumentation and intracanal dressing with Ca(OH)2 pastes

OBJECTIVE:The purpose of this study was to evaluate the distribution of microorganisms in the root canal system (RCS) and periapical lesions of dogs' teeth after rotary instrumentation and placement of different calcium hydroxide [Ca(OHy-based intracanal dressings.MATERIALS AND METHODS:Chronic periapical lesions were experimentally induced in 80 premolar roots of four dogs. Instrumentation was undertaken using the ProFile rotary system and irrigation with 5.25% sodium hypochlorite. The following Ca(OH)2-based pastes were applied for 21 days: group 1 - Calen (n=18); group 2 - Calen+CPMC (n=20); group 3 - Ca(OH2 p.a. + anaesthetic solution (n=16) and group 4 - Ca(OH2 p.a.+ 2% chlorhexidine digluconate (n=18). Eight root canals without endodontic treatment constituted the control group. Histological sections were obtained and stained with Brown & Brenn staining technique to evaluate the presence of microorganisms in the main root canal, ramifications of the apical delta and secondary canals, apical cementoplasts, dentinal tubules, areas of cemental resorption and periapical lesions. The results were analyzed statistically by the Mann-Whitney U test (p<0.05).RESULTS:The control group showed the highest prevalence of microorganisms in all sites evaluated. Gram-positive cocci, bacilli and filaments were the most frequent morphotypes. Similar microbial distribution patterns in the RCS and areas of cementum resorption were observed in all groups (p>0.05). The percentage of RCS sites containing microorganisms in groups 1, 2, 3, 4 and control were: 67.6%, 62.5%, 78.2%, 62.0% and 87.6%, respectively.CONCLUSION:In conclusion, the histomicrobiological analysis showed that the rotary instrumentation and the different calcium hydroxide pastes employed did not effectively eliminate the infection from the RCS and periapical lesions. However, several bacteria seen in the histological sections were probably dead or were inactivated by the biomechanical preparation and calcium hydroxide-based intracanal dressing.