Catchment-scale biogeography of riverine bacterioplankton

Abstract

Lotic ecosystems such as rivers and streams are unique in that they represent a continuum of both space and time during the transition from headwaters to the river mouth. As microbes have very different controls over their ecology, distribution and dispersion compared with macrobiota, we wished to explore biogeographical patterns within a river catchment and uncover the major drivers structuring bacterioplankton communities. Water samples collected across the River Thames Basin, UK, covering the transition from headwater tributaries to the lower reaches of the main river channel were characterised using 16S rRNA gene pyrosequencing. This approach revealed an ecological succession in the bacterial community composition along the river continuum, moving from a community dominated by Bacteroidetes in the headwaters to Actinobacteria-dominated downstream. Location of the sampling point in the river network (measured as the cumulative water channel distance upstream) was found to be the most predictive spatial feature; inferring that ecological processes pertaining to temporal community succession are of prime importance in driving the assemblages of riverine bacterioplankton communities. A decrease in bacterial activity rates and an increase in the abundance of low nucleic acid bacteria relative to high nucleic acid bacteria were found to correspond with these downstream changes in community structure, suggesting corresponding functional changes. Our findings show that bacterial communities across the Thames basin exhibit an ecological succession along the river continuum, and that this is primarily driven by water residence time rather than the physico-chemical status of the river.

Altitudinal patterns of diversity and functional traits of metabolically active microorganisms in stream biofilms

“…Our study thus paves the way toward new mechanistic understanding of microbial diversity patterns in streams, and further supports the notion that microorganisms exhibit distributional patterns along the fluvial continuum (Besemer et al, 2013;Read et al, 2014;Savio et al, 2014) as recognised for invertebrates (Vannote et al, 1980). These findings may have broader impacts as the treeline moves upwards because of climate warming in the Alps.…”

“…The relationships between downstream shifts in resources (i.e., primarily autochthonous sources upstream versus more allochthonous sources downstream), hydrogeomorphology and biotic communities have been described by the River Continuum Concept (Vannote et al, 1980). Microorganisms were not encapsulated in the River Continuum Concept, and yet evidence increasingly suggests that microbial communities predictably change along the river continuum (Besemer et al, 2013;Read et al, 2014;Savio et al, 2014). However, the potential drivers of these patterns remain poorly understood, which is noticeable, given the relevance of microorganisms for stream ecosystem functions (Battin et al, 2008).…”

Competition and protist predation are important regulators of riverine bacterial community composition and size distribution

“…Cytophaga-Flavobacteria were not found in this study, in contrast with many studies where Bacteroidetes have been found to be a frequent component of the riverine bacterial community (Crump et al 2009;Read et al 2015) or the main group forming filamentous cells under high grazing pressure (Salcher et al 2005). On the contrary, other studies (Puddu et al 2003;Crespo et al 2013) have demonstrated that Cytophaga-Flavobacteria are usually enriched on particulate organic detritus, and they could be specialists for particulate organic matter degradation, which was removed by filtration in this experiment.…”

Geographic distribution pattern of low and high nucleic acid content bacteria on a river-catchment scale

“…In contrast, there was a higher proportion of LNA bacteria found in the coastal Canet lagoon (57%; Servais et al 2003), eastern Mediterranean Sea (65%), North Atlantic (64%; Li et al 1995) and the Gulf of Mexico (62%; Jochem et al 2004). In comparison, only a few reports are available on LNA and HNA bacteria in freshwater environments (Ni et al 2015;Read et al 2015). For example, Joux and colleagues investigated the percentages of LNA and HNA bacteria and the effect of salinity and chlorophyll-a on those two groups along the Rhone River (France) (Joux et al 2005).…”

“…Wang and colleagues isolated three typical pure cultures of LNA that were closely affiliated to Polynucleobacter from freshwater environments in Switzerland (Wang et al 2009). To the best of our knowledge, field data on the spatial distribution patterns of LNA and HNA fractions are very scarce in freshwater environments (Ni et al 2015;Read et al 2015), and there is no information concerning the changes in cytometric characteristics of LNA and HNA bacteria on a large river-catchment scale. In the current study, we profiled the relationship between the cytometric characteristics of LNA and HNA bacteria, illustrated the biogeographical patterns (i.e.…”