Seasonal growth potential of rare lake water bacteria suggest their disproportional contribution to carbon fluxes

Abstract

We studied the seasonal growth potential of opportunistic bacterial populations in Lake Zurich (Switzerland) by a series of grazer-free dilution culture assays. Pronounced shifts in the composition of the bacterial assemblages were observed within one doubling of total cell numbers, from initially abundant Actinobacteria to other fast-growing microbial lineages. Small populations with growth potentials far above community average were detected throughout the year with striking seasonal differences in their respective taxonomic affiliations. Members of Cytophaga-Flavobacteria (CF) were disproportionally proliferating only during phytoplankton blooms in spring and summer, while Beta-and Gammaproteobacteria showed superior growth at all other occasions. Growth rates of Alphaproteobacteria and esp. Sphingomonadaceae were significantly correlated to water temperatures and were far above community average in summer. Within the genus Flavobacterium, two species-like populations showed a tendency for fast growth in most experiments, while four others were exclusively proliferating either during a spring or during a summer phytoplankton bloom. Their high growth potentials but low in situ abundances hint at a tight control by bacterivorous grazers and at a consequently accelerated carbon flux to higher trophic levels.

Climate‐related changes of soil characteristics affect bacterial community composition and function of high altitude and latitude lakes

“…These results are particularly relevant because the contribution of different taxa to the uptake of C and P substrates greatly affects the energy and nutrient supply to aquatic food webs (Šimek et al ., 2005; Salcher et al ., 2007). Our findings agree with a recent study showing that in grazer‐free incubations, and particularly during periods of high organic matter loadings, rare taxa dominated bacterial community composition (Neuenschwander et al ., 2015). The authors suggested that the low abundance of these taxa at natural settings is controlled by bacterivorous grazing, implying that their biomass contributes substantially to the C channelled towards higher trophic levels.…”

Lifestyles of rarity: understanding heterotrophic strategies to inform the ecology of the microbial rare biosphere

“…Rare soil taxa that were below detection not only responded to pulses of precipitation by blooming but also contributed to increased carbon dioxide and methane production, demonstrating that rare taxa collectively can contribute to ecosystem function (Aanderud et al 2015). Similarly, typically rare but fast-growing, cultivable taxa from Lake Zurich, Switzerland, could offer substantial contributions to carbon cycling (Neuenschwander et al 2015). A latitudinal analysis of marine bacterioplankton showed that fewer rare taxa are detectable in polar waters, possibly because these communities comprise fewer but more abundant taxa (Amend et al 2013).…”

“…Notably, the classification of a microorganism as an oligotroph or a copiotroph is separate from the habitat in which it resides (Semenov 1991, but see Koch 2001 for an opposing definition); both oligotrophic and copiotrophic microorganisms can persist in both low-and high-productivity environments. Indeed, populations of each strategy may complement each other in their dynamics in seasonally fluctuating or heterogeneous environments (Neuenschwander et al 2015).…”

“…One important distinguishing microbial trait is trophic strategy. Determining the strategies of heterotrophic bacteria has a long legacy in microbial ecology and has experienced a recent reinvigoration of interest (Giovannoni & Stingl 2007, Livermore et al 2014, Neuenschwander et al 2015. The conceptual delineation falls between oligotrophic and copiotrophic heterotrophs, which are generally defined by growth rate and responsiveness to local increases in resources.…”

“…The conceptual delineation falls between oligotrophic and copiotrophic heterotrophs, which are generally defined by growth rate and responsiveness to local increases in resources. Understanding the balance between oligotrophic and copiotrophic microbial strategies is of particular interest in aquatic systems, where both strategies contribute to temporal and spatial dynamics of community structure and may play different roles in the transfer of nutrients in aquatic food webs (Neuenschwander et al 2015).…”