Temporal Dynamics Of Bacterial Communities Research Articles

Temporal and fertilizer-dependent dynamics of soil bacterial communities in buckwheat fields under long-term management

This study integrated bacterial community and soil chemicals to characterize the soil ecosystem in an open upland field managed by six controlled fertilizer programs using the minimum amount of pesticides. Amplicon sequencing the 16S rRNA gene revealed that inorganic nitrogen fertilizer and compost altered the diversity and structure of the soil bacterial community throughout buckwheat (Fagopyrum esculentum Moench ‘Hitachiakisoba’) cultivation. The bacterial community comprised three clusters that contained bacteria that are prevalent in soils fertilized with nitrogen (cluster 1, 340 taxa), without nitrogen and compost (cluster 2, 234 taxa), and with compost-fertilized (cluster 3, 296 taxa). Cluster 2 contained more taxa in Actinobacteriota and less in Acidobacteriota, and cluster 3 contained more taxa in Gemmatimonadota compared with the other clusters. The most frequent taxa in cluster 1 were within the Chloroflexi phylum. The bacterial community structure correlated with soil chemical properties including pH, total organic carbon, SO42−, soluble Ca2+. A co-occurrence network of bacterial taxa and chemicals identified key bacterial groups comprising the center of a community network that determined topology and dynamics of the network. Temporal dynamics of the bacterial community structure indicated that Burkholderiales were associated with buckwheat ripening, indicating plant-bacteria interaction in the ecosystem.

Bacterial community shifts of commercial apples, oranges, and peaches at different harvest points across multiple growing seasons.

Assessing the microbes present on tree fruit carpospheres as the fruit enters postharvest processing could have useful applications, as these microbes could have a major influence on spoilage, food safety, verification of packing process controls, or other aspects of processing. The goal of this study was to establish a baseline profile of bacterial communities associated with apple (pome fruit), peach (stone fruit), and Navel orange (citrus fruit) at harvest. We found that commercial peaches had the greatest bacterial richness followed by oranges then apples. Time of harvest significantly changed bacterial diversity in oranges and peaches, but not apples. Shifts in diversity varied by fruit type, where 70% of the variability in beta diversity on the apple carposphere was driven by the gain and loss of species (i.e., nestedness). The peach and orange carposphere bacterial community shifts were driven by nearly an even split between turnover (species replacement) and nestedness. We identified a small core microbiome for apples across and between growing seasons that included only Methylobacteriaceae and Sphingomonadaceae among the samples, while peaches had a larger core microbiome composed of five bacterial families: Bacillaceae, Geodermtophilaceae, Nocardioidaceae, Micrococcaeceae, and Trueperaceae. There was a relatively diverse core microbiome for oranges that shared all the families present on apples and peaches, except for Trueperaceae, but also included an additional nine bacterial families not shared including Oxalobacteraceae, Cytophagaceae, and Comamonadaceae. Overall, our findings illustrate the important temporal dynamics of bacterial communities found on major commercial tree fruit, but also the core bacterial families that constantly remain with both implications being important entering postharvest packing and processing.

Role of traveling microplastics as bacterial carriers based on spatial and temporal dynamics of bacterial communities

Microplastics (MPs) are considered as distinct substrates for bacterial colonization, they can carry bacterial communities to travel around environments. The bacterial communities on traveling MPs prefer to be gradually consistent with those on local MPs that were always in the same environment, and this process of change in the bacterial communities on traveling MPs was called ‘localization’. However, the dynamics of localization process and their influencing factors are still unclear. Therefore, we simulated the MPs migration process along the water flow direction in the estuary. We used quantitative analysis to study the dynamics of bacterial communities on the migrated MPs. We found the localization characteristics depended on the differences between the former and latter environments, as well as the preexisting bacteria. The localization degree was higher when the former and latter environments were similar. In most cases, compared with the first cultivation of pristine MPs, the time for localization was shorter. Moreover, although the entire bacterial communities tended to be localized, the preexisting bacteria on the migrated MPs had selective effects on subsequent bacterial colonization. Furthermore, the preexisting bacteria on MPs could set up the connections with the bacteria that existed at the latter site, and the stability of the entire bacterial communities on the migrated MPs increased with time. Overall, our findings indicated that the localization characteristics of bacterial communities on traveling MPs were related to the precultured time and environmental differences, which were helpful to understand the colonized bacteria transportation and MPs ecological effects.

Temporal variation in bacterial community profile on patients' bedsheets in a primary healthcare unit.

Fabrics serve as fomites in spreading nosocomial infections. As a patient is in close contact with bedsheets, it is important to assess the seasonal variation in bacterial diversity on these in healthcare units. The study was conducted to characterise the bacterial diversity on patients' bedsheets across 7months in a primary healthcare unit. Polyester-cotton blend fabric was stitched on bedsheets, and temporal dynamics of bacterial communities was assessed from May to November 2019. qPCR and amplicon sequencing of 16S rRNA gene was performed for profiling of bacterial community. Results revealed the dominance of Bacillota followed by Pseudomonadota, and Actinomycetota. A seasonal variation was observed in the bacterial load, with maximum values in June. This indicates the impact of environmental conditions on bacterial abundance and composition on fabrics in healthcare unit. The presence of priority pathogens on the patient bedsheets is a human health concern reiterating the need for season-specific laundering protocol.

Temporal Dynamics of Bacterial Communities along a Gradient of Disturbance in a U.S. Southern Plains Agroecosystem.

ABSTRACTLand conversion for intensive agriculture produces unfavorable changes to soil ecosystems, causing global concern. Soil bacterial communities mediate essential terrestrial ecosystem processes, making it imperative to understand their responses to agricultural perturbations. Here, we used high-throughput sequencing coupled with a functional gene array to study temporal dynamics of soil bacterial communities over 1 year under different disturbance intensities across a U.S. Southern Plains agroecosystem, including tallgrass prairie, Old World bluestem pasture, no-tillage (NT) canola, and conventional tillage (CT) wheat. Land use had the greatest impact on bacterial taxonomic diversity, whereas sampling time and its interaction with land use were central to functional diversity differences. The main drivers of taxonomic diversity were tillage > sampling time > temperature, while all measured factors explained similar amounts of variations in functional diversity. Temporal differences had the strongest correlation with total nitrogen > rainfall > nitrate. Within land uses, community variations for CT wheat were attributed to nitrogen levels, whereas soil organic matter and soil water content explained community variations for NT canola. In comparison, all measured factors contributed almost equally to variations in grassland bacterial communities. Finally, functional diversity had a stronger relationship with taxonomic diversity for CT wheat compared to phylogenetic diversity in the prairie. These findings reinforce that tillage management has the greatest impact on bacterial community diversity, with sampling time also critical. Hence, our study highlights the importance of the interaction between temporal dynamics and land use in influencing soil microbiomes, providing support for reducing agricultural disturbance to conserve soil biodiversity.

Bacterial Dynamics and Their Influence on the Biogeochemical Cycles in a Subtropical Hypereutrophic Lake During the Rainy Season.

Lakes in subtropical regions are highly susceptible to eutrophication due to the heavy rainfall, which causes significant runoff of pollutants (e.g., nutrients) to reach surface waters, altering the water quality and influencing the microbial communities that regulate the biogeochemical cycles within these ecosystems. Lake Cajititlán is a shallow, subtropical, and endorheic lake in western Mexico. Nutrient pollution from agricultural activity and wastewater discharge have affected the lake’s water quality, leading the reservoir to a hypereutrophic state, resulting in episodes of fish mortality during the rainy season. This study investigated the temporal dynamics of bacterial communities within Lake Cajititlán and their genes associated with the nitrogen, phosphorus, sulfur, and carbon biogeochemical cycles during the rainy season, as well as the influences of physicochemical and environmental variables on such dynamics. Significant temporal variations were observed in the composition of bacterial communities, of which Flavobacterium and Pseudomonas were the dominant genera. The climatological parameters that were most correlated with the bacterial communities and their functional profiles were pH, DO, ORP, turbidity, TN, EC, NH4+, and NO3–. The bacterial communities displayed variations in their functional composition for nitrogen, phosphorus, and sulfur metabolisms during the sampling months. The bacterial communities within the lake are highly susceptible to nutrient loads and low DO levels during the rainy season. Bacterial communities had a higher relative abundance of genes associated with denitrification, nitrogen fixation, assimilatory sulfate reduction, cysteine, SOX system, and all phosphorus metabolic pathways. The results obtained here enrich our understanding of the bidirectional interactions between bacterial communities and major biogeochemical processes in eutrophic subtropical lakes.

Resource aromaticity affects bacterial community successions in response to different sources of dissolved organic matter

Microbe-mediated transformation of dissolved organic matter (DOM) contributes substantially to the carbon dynamics and energy flow of aquatic ecosystems; yet, the temporal dynamics of bacterial communities in response to diverse DOM sources are scarcely known. Here, we supplied four distinct sources of DOM (algae-derived, macrophyte-derived, sewage-derived, and soil-derived) to the same bacterial community to track the effects of these DOM sources on the carbon processing and successional dynamics of bacterial communities. Although by the end of the incubation the proportion of bio-degraded DOM was significantly lower in the soil-derived DOM treatment than for the other sources, rapid initial metabolism of protein-like and aliphatic compounds and increasing aromaticity and humification degree of DOM during the incubation period were observed for all sources. The role of stochastic processes in governing the community assembly decreased substantially from 61.4% on the first day to 16.7% at the end of the incubation. Moreover, stronger deterministic selection and lower temporal turnover rate were observed for the soil-derived than the other DOM sources, indicating stronger environmental filtering by the more aromatic DOM. Significant correlations were also observed between the humification index (HIX) of DOM and bacterial community diversities, co-occurrence patterns, habitat niche breadths, and the contribution of deterministic ecological processes. In addition, we demonstrated that taxa with different abundance patterns all play crucial but different roles in the response to DOM variation. Our results indicate the importance of DOM aromaticity as a predictor of the outcome of different DOM sources on bacterial community dynamics.

Temporal dynamics of bacterial communities during seed development and maturation.

Seed microbiota acts as a starting point for the assembly of the plant microbiota and contributes to successful plant establishment. To date, the order and timing of microbial taxa immigration during seed development and maturation remained unknown. We investigated the temporal dynamics of seed bacterial communities in bean and radish. A high phylogenetic turnover was observed for both plant species with few taxa associated with all seed developmental stages. Greater heterogeneity in communities structure within each stage was observed for radish. While, about one-third of radish seed bacterial taxa were detected in buds, flowers and fruits, very few taxa seem to be transmitted by the floral route in bean. In the latter species, bacterial populations belonging to the P. fluorescens species complex were found either in buds, flowers and fruits or in seeds. The relative phylogenetic proximity of these bacterial populations combined with their habitat specificity led us to explore the genetic determinants involved in successful seed transmission in bean. Comparative genomic analyses of representatives bacterial strains revealed dozens of coding sequences specifically associated with seed-transmitted strains. This study provided a first glimpse on processes involved in seed microbiota assembly, which could be used for designing plant-beneficial microbial consortia.

Ecological insights into assembly processes and network structures of bacterial biofilms in full-scale biologically active carbon filters under ozone implementation

To address the adverse effects of harmful algal blooms, there are increased demands over the implementation of ozone coupled with biologically active carbon (BAC) filters in the drinking water treatment plants. Although the microbial biofilms are vital elements to support the proper performance of BAC filters, except for taxonomic affiliations, little is known about the assembly mechanisms of microbial communities in the full-scale BAC filters. This study aimed to examine how the assembly processes and their associated factors (e.g., influent characteristics, biological interactions) drive the temporal dynamics of bacterial communities in full-scale BAC filters, which underwent ozone implementation (five consecutive seasons from 2017 to 2018). The results revealed that along with the increase of bacterial taxonomic richness and evenness, stochastic processes became more crucial to determine the bacterial community assembly in the summer and autumn after ozone implementation (relative contribution: 61.23% and 83.75%, respectively). Moreover, their corresponding networks possessed simple network structures with lower modularity than other seasons, which implied lesser biological interactions among bacterial populations. The correlation between taxonomic and predicted functional diversities using functional redundancy index indicated that relatively high levels of bacterial functional redundancy (>0.83) were generally present in BAC filters. However, compared to other seasons, significantly higher degrees of functional redundancy existed in the summer and autumn after ozone implementation (0.85 ± 0.01 and 0.86 ± 0.01, respectively). Overall, this work improves our understanding of the microbial ecology of full-scale BAC filters by providing a conceptual framework that characterizes bacterial biofilm assembly processes relevant to performance optimization of full-scale BAC filters.

Temporal dynamics of bacterial communities in the water and sediments of sea cucumber (Apostichopus japonicus) culture ponds

Bacteria communities in the aquaculture environment have been shown to greatly influence the growth of culture species. The sea cucumber (Apostichopus japonicus) is one of the most important aquaculture species in China, with numerous economic benefits. The growth and physiological characteristics of A. japonicus exhibit remarkable seasonal variation. However, current knowledge regarding the bacterial communities in A. japonicus culture ponds and their potential roles in the regulation of A. japonicus growth and physiology remain unclear. In the present study, Illumina sequencing based on the bacterial 16S rRNA gene was used to investigate the variations in bacterial communities in the surface water and sediment of A. japonicus culture ponds for a period of 1 year. The sediments exhibited a higher diversity of bacterial communities, and a higher abundance of microorganisms involved in sulfur metabolism; however, the surface water had a higher abundance of bacterial species associated with the degradation of organic matter. Furthermore, the bacterial communities in the water column showed a “3 + 1” monthly pattern and those in the sediments exhibited a seasonal succession. The higher abundances of bacteria associated with organic pollution degradation and functions associated with bio-active compound secretion were detected in water samples collected in April, August, and December. In contrast, bacteria that are considered to be food sources for A. japonicus were more abundant in pond sediments in autumn and spring. Finally, correlation analysis demonstrated that water temperature negatively regulated the sulfur cycling efficiency of bacterial communities in sediments of A. japonicus culture ponds. This study provides an important theoretical basis for the micro-ecological regulation of pond-cultured A. japonicus.

Temporal Dynamics of Bacterial Communities in a Pilot-Scale Vermireactor Fed with Distilled Grape Marc.

Vermicomposting has been found as a profitable approach to dispose of and treat large quantities of raw grape marc. However, less information is available with regard to its efficiency for treating distillery winery byproducts, even though distillation has been widely used as a way to economically valorize grape marc. As such, we sought to characterize the compositional and functional changes in bacterial communities during vermicomposting of distilled grape marc by using 16S rRNA high-throughput sequencing. Samples were collected at the initiation of vermicomposting and at days 14, 21, 28, 35 and 42. There were significant changes (p < 0.0001) in the bacterial community composition of distilled grape marc after 14 days of vermicomposting that were accompanied by twofold increases in bacterial richness and diversity from a taxonomic and phylogenetic perspective. This was followed by significant increases in functional diversity of the bacterial community, including metabolic capacity, lignin and cellulose metabolism, and salicylic acid synthesis. These findings indicate that the most striking compositional and functional bacterial community changes took place during the active phase of the process. They also pinpoint functional attributes that may be related to the potential beneficial effects of distilled grape marc vermicompost when applied on soil and plants.

Bacterial and algal symbiont dynamics in early recruits exposed to two adult coral species

Corals live in a symbiotic relationship with various microorganisms including bacteria, some of which are essential for host health and survival. Bacterial assemblages are typically highly diverse in juveniles and are speculated to exert roles critical to coral ontogenetic development. However, knowledge about bacterial dynamics in coral recruits is scarce, especially in brooders. In this study, we investigated the temporal dynamics of bacterial communities associated with Pocillopora acuta early recruits exposed to different microbial environments. One week after settlement, recruits were grown in a flow-through system with 0.4 µm filtered seawater either alone, or in the vicinity of adult Pocillopora acuta or Platygyra daedalea coral fragments, which associate with different microbiomes. After 5 weeks, all corals were transferred to a mesocosm containing various marine organisms, where they were reared for another 4 weeks. In addition to observing the development of coral-associated microbial communities, we assessed whether exposing Pocillopora acuta recruits to different adult coral species influenced their bacterial communities. Our motivation was to examine whether this approach can be used to modify bacteria and Symbiodiniaceae associated with these early life stages. While adult Pocillopora acuta fragments had bacterial assemblages dominated by Endozoicomonadaceae, bacterial communities of Platygyra daedalea fragments were dominated by Flammeovirgaceae and Rhodospirillaceae. Bacterial communities associated with recruits were more diverse than those found in adults and contained larger relative abundances of Flavobacteriaceae, Rhodobacteraceae and Erythrobacteraceae. All recruits harbored the same Symbiodiniaceae type throughout the experiment (dominated by Cladocopium C1d sequences), and their bacterial communities did not differ across treatments. Instead, there was a significant change over time characterized by a decline in the relative abundance of Flavobacteriaceae and an increase in the abundance of Endozoicomonadaceae. Our findings indicate that Pocillopora acuta recruits harbor dynamic and diverse bacterial assemblages, which were not influenced by nearby adult corals in our experimental design.

Bacterial colonization of minerals in grassland soils is selective and highly dynamic.

Bacteria colonize reactive minerals in soils where they contribute to mineral weathering and transformation. So far, the specificity, patterns and dynamics of mineral colonization have rarely been assessed under natural conditions. High throughput Illumina sequencing was employed to investigate the bacterial communities assembling on illite and goethite during exposure to natural grassland soils. Two different types of organic carbon sources, simple carbon compounds representing root exudates and detritus of two dominant grassland plant species were applied, and their effects on the temporal dynamics of bacterial communities were investigated. The observed temporal patterns suggest that the surfaces of de novo exposed minerals in soils drive the establishment of bacterial communities and override the effect of the type of carbon sources and of other environmental properties. Mineral colonization was selective and specific bacterial sequence variants exhibited distinct colonization patterns, among which early, intermittent, and late colonizers could be distinguished. Based on our results, soil minerals are not only colonized by specific bacterial communities but enable a succession of different bacterial communities. Our results thereby expand the concept of the mineralosphere and provide novel insights into mechanisms of community assembly in the soil ecosystem.

Temporal Dynamics of Bacterial Communities in Soil and Leachate Water After Swine Manure Application.

Application of swine manure to agricultural land allows recycling of plant nutrients, but excess nitrate, phosphorus and fecal bacteria impact surface and drainage water quality. While agronomic and water quality impacts are well studied, little is known about the impact of swine manure slurry on soil microbial communities. We applied swine manure to intact soil columns collected from plots maintained under chisel plow or no-till with corn and soybean rotation. Targeted 16S-rRNA gene sequencing was used to characterize and to identify shifts in bacterial communities in soil over 108 days after swine manure application. In addition, six simulated rainfalls were applied during this time. Drainage water from the columns and surface soil were sampled, and DNA was extracted and sequenced. Unique DNA sequences (OTU) associated with 12 orders of bacteria were responsible for the majority of OTUs stimulated by manure application. Proteobacteria were most prevalent, followed by Bacteroidetes, Firmicutes, Actinobacteria, and Spirochaetes. While the majority of the 12 orders decreased after day 59, relative abundances of genes associated with Rhizobiales and Actinomycetales in soil increased. Bacterial orders which were stimulated by manure application in soil had varied responses in drainage waters over the course of the experiment. We also identified a “manure-specific core” of five genera who comprised 13% of the manure community and were not significantly abundant in non-manured control soils. Of these five genera, Clostridium sensu stricto was the only genus which did not return to pre-manure relative abundance in soil by day 108. Our results show that enrichment responses after manure amendment could result from displacement of native soil bacteria by manure-borne bacteria during the application process or growth of native bacteria using manure-derived available nutrients.

Building a Translational Microbiome Toolbox

Designing successful microbiota-based therapies requires in-depth understanding of the ecological foundations of this community. In this issue, two studies by Whitaker etal. and Lim etal. provide refined genetic tools for dissecting the spatial organization and temporal dynamics of bacterial communities at the single-cell and -gene levels.

Temporal dynamics of bacterial communities and predicted nitrogen metabolism genes in a full-scale wastewater treatment plant

Dynamics of bacterial communities and nitrogen metabolism genes in a full-scale WWTP as revealed by Illumina sequencing and PICRUSt.

Bacterial succession along a long-term chronosequence of paddy soil in the Yangtze River Delta, China

Conversion of tidal wetlands into paddy soils is an ancient and prevalent agricultural practice to meet increasing demand of food in the Yangtze River Delta of China, a coastal region where paddy soils originated. However, the impacts of tidal wetland reclamation and continuous rice cultivation at long time scales on soil bacterial communities remains poorly understood. In this study, we investigated temporal dynamics of bacterial communities using 16S rRNA gene pyrosequencing to delineate the patterns and drivers of soil bacterial succession along a long-term (2000 years) chronosequence of paddy field since reclamation from tidal wetlands. The results exhibited orderly changes in soil physicochemical characteristics and bacterial community composition with increasing rice cultivation time, indicating the occurrence of paddy soil development and bacterial succession since reclamation from tidal wetlands. Soil bacterial diversity significantly increased after reclamation of tidal wetlands. Succession of bacterial community composition was primarily linked with significant decrease in the relative abundances of Gammaproteobacteria and Planctomycetes and increase in those of Alphaproteobacteria and Firmicutes. Further analysis showed that long-term rice cultivation led to the enrichment of certain populations such as Rhodospirillaceae (within the class Alphaproteobacteria) and Clostridiaceae (within the phylum Firmicutes), which are potentially beneficial to higher rice yields. Canonical correspondence analysis indicated that at the time scale of millennia, the shift of bacterial community structure was mainly driven by the changes of soil physicochemical properties, especially cation exchange capacity and pH during paddy soil development. Overall, we demonstrate an orderly shift of soil bacterial communities towards higher productivity along with a 2000-year development of paddy soils after the tidal wetland reclamation, which was primarily associated with soil physicochemical alterations with time, and suggest that such chronosequence of paddy soils can serve as a test bed to delineate the relationship between microbial community and soil functions, particularly crop productivity.

BACTERIOPLANCTON EN BAHÍA GAIRA, MAR CARIBE (COLOMBIA): COMPARACIÓN DE LA VARIABILIDAD EN ABUNDANCIA Y BIOMASA BACTERIANA DURANTE DIFERENTES PERÍODOS

Marine bacterioplankton abundance, biomass, biovolume and shape were quantied in three stations within Gaira Bay at the Colombian Caribbean coast over three periods dened for this study as: “rainy” (July, August, 2003), “transition” (April, October 2004) and “dry” (February, March, 2004). Bacterioplankton samples were collected from 0.5 and 42 m depths, ltered onto 0.22 μm polycarbonate lters and quantied using epi!uorescence microscopy with Acridine Orange staining and image analysis. Average bacterial abundance ranged between 1.3 x 105-2.9 x 106 cells mL-1 during the rainy period, 8.8 x 104-2.2 x 106 cells mL-1 during the transition period and 6.7 x 104-3.9 x 105 cell mL-1 at the dry period, with a mean abundance of 4.4 x 105 cells mL-1. The differences in abundance were statistically signicant between sampling periods, stations and depths, the differences in biovolume were statistically signicant between sampling periods and stations, nally, the differences in biomass were statistically signicant between stations and water depths (ANOVA, p&lt;0.05). Most of the cells had a coccoid shape and a small biovolume (0.01-0.08 μm3 cell-1). Over the sampling period, the mean bacterial biomass ranged between 0.88 and 32.1 μg C L-1, with the maximum observed during the rainy period. The results suggest that bacterial biomass increases during the rainy period, probably as a consequence of increased water discharge originating from the Gaira River and the Ciénaga Grande de Santa Marta lagoon. We hypothesize that the temporal dynamics of bacterial communities in Gaira Bay are being driven by the availability of organic nutrients (DOC).

The impact of sampling, PCR, and sequencing replication on discerning changes in drinking water bacterial community over diurnal time-scales

High-throughput and deep DNA sequencing, particularly amplicon sequencing, is being increasingly utilized to reveal spatial and temporal dynamics of bacterial communities in drinking water systems. Whilst the sampling and methodological biases associated with PCR and sequencing have been studied in other environments, they have not been quantified for drinking water. These biases are likely to have the greatest effect on the ability to characterize subtle spatio-temporal patterns influenced by process/environmental conditions. In such cases, intra-sample variability may swamp any underlying small, systematic variation. To evaluate this, we undertook a study with replication at multiple levels including sampling sites, sample collection, PCR amplification, and high throughput sequencing of 16S rRNA amplicons. The variability inherent to the PCR amplification and sequencing steps is significant enough to mask differences between bacterial communities from replicate samples. This was largely driven by greater variability in detection of rare bacteria (relative abundance <0.01%) across PCR/sequencing replicates as compared to replicate samples. Despite this, we captured significant changes in bacterial community over diurnal time-scales and find that the extent and pattern of diurnal changes is specific to each sampling location. Further, we find diurnal changes in bacterial community arise due to differences in the presence/absence of the low abundance bacteria and changes in the relative abundance of dominant bacteria. Finally, we show that bacterial community composition is significantly different across sampling sites for time-periods during which there are typically rapid changes in water use. This suggests hydraulic changes (driven by changes in water demand) contribute to shaping the bacterial community in bulk drinking water over diurnal time-scales.

Activity and bacterial diversity of snow around Russian Antarctic stations

The diversity and temporal dynamics of bacterial communities in pristine snow around two Russian Antarctic stations was investigated. Taxonomic analysis of rDNA libraries revealed that snow communities were dominated by bacteria from a small number of operational taxonomic units (OTUs) that underwent dramatic swings in abundance between the 54th (2008–2009) and 55th (2009–2010) Russian Antarctic expeditions. Moreover, analysis of the 55th expedition samples indicated that there was very little, if any, correspondence in abundance of clones belonging to the same OTU present in rDNA and rRNA libraries. The latter result suggests that most rDNA clones originate from bacteria that are not alive and/or active and may have been deposited on the snow surface from the atmosphere. In contrast, clones most abundant in rRNA libraries (mostly belonging to Variovorax, Janthinobacterium, Pseudomonas, and Sphingomonas genera) may be considered as endogenous Antarctic snow inhabitants.