Stream microbial diversity in response to environmental changes: review and synthesis of existing research

Abstract

The importance of microbial activity to ecosystem function in aquatic ecosystems is well established, but microbial diversity has been less frequently addressed. This review and synthesis of 100s of published studies on stream microbial diversity shows that factors known to drive ecosystem processes, such as nutrient availability, hydrology, metal contamination, contrasting land-use and temperature, also cause heterogeneity in bacterial diversity. Temporal heterogeneity in stream bacterial diversity was frequently observed, reflecting the dynamic nature of both stream ecosystems and microbial community composition. However, within-stream spatial differences in stream bacterial diversity were more commonly observed, driven specifically by different organic matter (OM) compartments. Bacterial phyla showed similar patterns in relative abundance with regard to compartment type across different streams. For example, surface water contained the highest relative abundance of Actinobacteria, while epilithon contained the highest relative abundance of Cyanobacteria and Bacteroidetes. This suggests that contrasting physical and/or nutritional habitats characterized by different stream OM compartment types may select for certain bacterial lineages. When comparing the prevalence of physicochemical effects on stream bacterial diversity, effects of changing metal concentrations were most, while effects of differences in nutrient concentrations were least frequently observed. This may indicate that although changing nutrient concentrations do tend to affect microbial diversity, other environmental factors are more likely to alter stream microbial diversity and function. The common observation of connections between ecosystem process drivers and microbial diversity suggests that microbial taxonomic turnover could mediate ecosystem-scale responses to changing environmental conditions, including both microbial habitat distribution and physicochemical factors.

The ecology and biogeochemistry of stream biofilms

“…Next-generation sequencing data of 16S rRNA genes (that is, bacterial taxonomic marker genes) of samples from benthic and hyporheic biofilms are becoming increasingly available [25][26][27] , which has enabled a more detailed understanding of the composition and diversity patterns of bacterial communities within stream biofilms. These data suggest that the Proteobacteria biopolymers, such as cellulose and chitin 28,29 , that contribute to the high molecular weight fraction of DOM in streams.…”

“…Stream biofilm communities are highly diverse with hundreds if not thousands of operational taxonomic units (OTUs) that span over the major taxa outlined above and colonize the 6 various habitats in streams 25 (FIGS 1,2). A major question that arises from these observations is how do these complex communities assemble?…”

“…Finally, the differentiation of stream biofilms into complex physical structures and the role of each of the various biological building blocks that contribute to this process also warrant more attention, if we are to be able to mechanistically link biodiversity to biofilm function. 25,95 . These environmental changes include shifts in precipitation patterns, damming and water diversion that profoundly alter the hydrological regime.…”

“…Microorganisms in streams are also major components of the nitrogen cycle as they denitrify nitrate that they receive from catchment and emit the resulting nitrous oxide or nitrogen gas into the atmosphere 11,12 . Next-generation sequencing data of 16S rRNA genes (that is, bacterial taxonomic marker genes) of samples from benthic and hyporheic biofilms are becoming increasingly available [25][26][27] , which has enabled a more detailed understanding of the composition and diversity patterns of bacterial communities within stream biofilms. These data suggest that the Proteobacteria Furthermore, depending on the turbulence of the water overlying the biofilms, the biofilm canopy can differentiate into streamers (see below), which can entail microscale shifts in bacterial community composition.…”

Halo-thermophilic bacteria and heterocyst cyanobacteria found adjacent to halophytes at Sabkhas, Qatar: Preliminary study and possible roles

“…Meteorological reports confirm that annual rainfall could be well below 80 mm, electrical conductivity of soil saturated extract (ECe) could be above 200 dSm -1 , and summer temperatures are known to exceed 50°C (AbdelBari et al, 2007;Yasseen and Al-Thani, 2013). These environmental factors can cause a host of changes in the microbial community and the biodiversity in desert ecosystems and habitats (Berg et al, 2014;Classen et al, 2015;Tang et al, 2015;Zeglin, 2015). The abundance and activities of soil microorganisms are determined by these environmental factors and the presence of organic matter, pollution, etc.…”