Microorganisms play pivotal roles within aquatic ecosystems, affecting their structure, functioning and services. However, little is known about the effects of water stratification and mixing on the aquatic microbial community dynamics in subtropical reservoirs. In this study, we explored vertical and seasonal patterns of microbial diversity in the Dongzhen Reservoir (southeast China). Quantitative PCR, quantitative RT-PCR, and 454 pyrosequencing were used for an in-depth characterization of the bacterial community across time (every three months for one year) and space (five different water depths). Our results indicated that thermal and oxygen stratification shaped the phylogenetic composition of microbial communities in the reservoir. There were significant differences in physical, chemical and microbiological parameters between epilimnion and hypolimnion (P < 0.05). The RNA: DNA ratios were significantly lower in epilimnion and metalimnion but rapidly increased in hypolimnion (P < 0.05), suggesting that microorganisms were more active at low temperatures, low dissolved oxygen concentrations and high TN/TP ratios. Redundancy analysis and pathway analysis revealed a complex interplay of various environmental and biological factors by explaining the spatiotemporal variations in bacterial communities. Adaptive reservoir management strategies should consider carefully the effects of water stratification and mixing, together with the distribution patterns of aquatic microorganisms.
Efflux pumps are membrane proteins involved in the active extrusion of a wide range of structurally dissimilar substrates from cells. A multidrug efflux pump named TetA belonging to the major facilitator superfamily (MFS) of transporters was identified in the Streptococcus thermophilus DSM 20617(T) genome. The tetA-like gene was found in the genomes of a number of S. thermophilus strains sequenced to date and in Streptococcus macedonicus ACA-DC 198, suggesting a possible horizontal gene transfer event between these two Streptococcus species, which are both adapted to the milk environment. Flow cytometry (single-cell) analysis revealed bistable TetA activity in the S. thermophilus population, and tetA-like gene over-expression resulted in a reduced susceptibility to ethidium bromide, tetracycline, and other toxic compounds even when the efflux pump was over-expressed in a strain naturally lacking tetA-like gene.
Flood and drought events of higher intensity and frequency are expected to increase in arid and semi-arid regions, in which temporary rivers represent both a water resource and an aquatic ecosystem to be preserved. In this study, we explored the variation of two classes of hazardous substances (Polycyclic Aromatic Hydrocarbons and Nonylphenols) and the functioning of the microbial community in river sediments subject to hydrological fluctuations (Candelaro river basin, Italy). Overall, the concentration of pollutants (?PAHs range 8-275ngg(-1); ?NPs range 299-4858ngg(-1)) suggests a moderate degree of contamination. The conditions in which the sediments were tested, flow (high/low) and no flow (wet/dry/arid), were associated to significant differences in the chemical and microbial properties. The total organic carbon contribution decreased together with the stream flow reduction, while the contribution of C-PAHs and C-NPs tended to increase. NPs were relatively more concentrated in sediments under high flow, while the more hydrophobic PAHs accumulated under low and no flow conditions. Passing from high to no flow conditions, a gradual reduction of microbial processes was observed, to reach the lowest specific bacterial carbon production rates (0.06fmolCh(-1)cell(-1)), extracellular enzyme activities, and the highest doubling time (40h) in arid sediments. In conclusion, different scenarios for the mobilization of pollutants and microbial processes can be identified under contrasting hydrological conditions: (i) the mobilization of pollutants under high flow and a relatively higher probability for biodegradation; (ii) the accumulation of pollutants during low flow and lower probability for biodegradation; (iii) the drastic reduction of pollutant concentrations under dry and arid conditions, probably independently from the microbial activity (abiotic processes). Our findings let us infer that a multiple approach has to be considered for an appropriate water resource exploitation and a more realistic prevision of the impact of pollutants in temporary waters.
The cryosphere is an integral part of the global climate system and one of the major habitable ecosystems of Earth's biosphere. These permanently frozen environments harbor diverse, viable and metabolically active microbial populations that represent almost all the major phylogenetic groups. In this study, we investigated the microbial diversity in the surface snow surrounding the Concordia Research Station on the High Antarctic Plateau through a polyphasic approach, including direct prokaryotic quantification by flow cytometry and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH), and phylogenetic identification by 16S RNA gene clone library sequencing and 454 16S amplicon pyrosequencing. Although the microbial abundance was low (<10(3) cells/ml of snowmelt), concordant results were obtained with the different techniques. The microbial community was mainly composed of members of the Alpha-proteobacteria class (e.g. Kiloniellaceae and Rhodobacteraceae), which is one of the most well-represented bacterial groups in marine habitats, Bacteroidetes (e.g. Cryomorphaceae and Flavobacteriaceae) and Cyanobacteria. Based on our results, polar microorganisms could not only be considered as deposited airborne particles, but as an active component of the snowpack ecology of the High Antarctic Plateau.
Playing your part: Conductive magnetite nanoparticles accelerate the microbial reductive dechlorination of trichloroethene (TCE), an ubiquitous and toxic subsurface contaminant. The stimulatory effect most likely results from the nanoparticles promoting the establishment of interspecies electron transfer (IET) processes between non-dechlorinating and dechlorinating microorganisms.
In Mediterranean intermittent streams, the hydrological fragmentation in summer and the successive water flow re-convergence in autumn allow exploring how local processes shape the microbial community within the same habitat. The objectives of this study were to determine how bacterial community composition responded to hydrological fragmentation in summer, and to evaluate whether the seasonal shifts in community composition predominate over the effects of episodic habitat fragmentation. The bacterial community was assessed along the intermittent stream Fuirosos (Spain), at different levels of phylogenetic resolution by in situ hybridization, fingerprinting, and 16S rRNA gene sequencing. The hydrological fragmentation of the stream network strongly altered the biogeochemical conditions with the depletion of oxidized solutes and caused changes in dissolved organic carbon characteristics. In the isolated ponds, beta-Proteobacteria and Actinobacteria increased their abundance with a gradual reduction of the alpha-diversity as pond isolation time increased. Moreover, fingerprinting analysis clearly showed a shift in community composition between summer and autumn. In the context of a seasonal shift, the temporary stream fragmentation simultaneously reduced the microbial dispersion and affected local environmental conditions (shift in redox regime and quality of the dissolved organic matter) tightly shaping the bacterioplankton community composition.
Flow cytometry and Fluorescence In Situ Hybridization are common methods of identifying and quantifying bacterial cells. The combination of cytometric rapidity and multi-parametric accuracy with the phylogenetic specificity of oligonucleotide FISH probes has been regarded as a powerful and emerging tool in aquatic microbiology. In the present work, tests were carried out on E. coli pure culture and marine bacteria using an in-solution hybridization protocol revealing high efficiency hybridization signal for the first one and a lower for the second one. Other experiments were conducted on natural samples following the established CARD-FISH protocol on filter performed in a closed system, with the aim of improving cell detachment and detection. The hybridized cells were then subsequently re-suspended from the membrane filters by means of an optimized detachment procedure. The cytometric enumeration of hybridized marine bacteria reached 85.7%±18.1% of total events. The quality of the cytograms suggests that the procedures described may be applicable to the cytometric quantification of phylogenetic groups within natural microbial communities.
Bacterial community composition was assessed during riverine biofilm development by the Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH) in combination with Confocal Laser Scanning Microscopy. Using artificial substrates, it was possible to follow the dynamics of specific bacterial clusters, while maintaining the unaltered structure and architecture of the biofilm.
Appropriate detachment treatments are required to analyze prokaryotes associated with streambed sediments by flow cytometry. Using our previously optimized protocol, two groups of cells exhibiting different nucleic acid contents were easily detectable. However, the Nucleic Acid Double Staining assay proved that detachment procedures negatively affect the cell membrane integrity.
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