Optimization of Biomass Composition Explains Microbial Growth-Stoichiometry Relationships

Abstract

Integrating microbial physiology and biomass stoichiometry opens far-reaching possibilities for linking microbial dynamics to ecosystem processes. For example, the growth-rate hypothesis (GRH) predicts positive correlations among growth rate, RNA content, and biomass phosphorus (P) content. Such relationships have been used to infer patterns of microbial activity, resource availability, and nutrient recycling in ecosystems. However, for microorganisms it is unclear under which resource conditions the GRH applies. We developed a model to test whether the response of microbial biomass stoichiometry to variable resource stoichiometry can be explained by a trade-off among cellular components that maximizes growth. The results show mechanistically why the GRH is valid under P limitation but not under N limitation. We also show why variability of growth rate-biomass stoichiometry relationships is lower under P limitation than under N or C limitation. These theoretical results are supported by experimental data on macromolecular composition (RNA, DNA, and protein) and biomass stoichiometry from two different bacteria. In addition, compared to a model with strictly homeostatic biomass, the optimization mechanism we suggest results in increased microbial N and P mineralization during organic-matter decomposition. Therefore, this mechanism may also have important implications for our understanding of nutrient cycling in ecosystems.

Rate of warming affects temperature sensitivity of anaerobic peat decomposition and greenhouse gas production

“…Here, we observed that increases in the amount or C content of the microbial biomass enhanced soil C loss in the ramp treatment, probably by increasing overall enzyme production (Allison et al, 2010;Kivlin et al, 2013;Manzoni et al, 2012). Alternatively, nutrient limitation in microbial biomass owing to the greater incorporation of C in biomass in the ramp treatment could also increase C loss through overflow respiration (Franklin, Hall, Kaiser, Battin, & Richter, 2011;Russell & Cook, 1995).…”

The return of an experimentally N-saturated boreal forest to an N-limited state: observations on the soil microbial community structure, biotic N retention capacity and gross N mineralisation

“…Firstly, the indications of stronger C limitation among bacteria in N loaded than in control plots (Demoling et al 2008;Kamble et al 2013), suggests that enhanced belowground C supply after termination of N load could stimulate growth and biomass. Secondly, enhanced N availability should favor bacteria (over ECM fungi) under C-limitation and under reduced tree belowground C allocation because of the relatively higher bacterial N demand per biomass C. Bacteria may thus support their biomass with less C per N assimilated under C-limitation than ECM fungi because of fundamental differences in their physiology and biomass C/N ratio (Keiblinger et al 2010;Franklin et al 2011). Moreover, our observation of higher sat/mono and cy/ pre ratios in N1-N2 than in N0 and N3 plots, have been associated with low C and/or high N availabilities (Bossio and Scow 1998;Allison et al 2005;van Diepen et al 2010;Zechmeister-Boltenstern et al 2011;Högberg et al 2013) thus supporting the explanation above.…”

Screening of Effective Markers for Mesophilic Bacterium Growth Using Factorial Experimental Design

“…Although the nutrient concentrations used in this work were inside the range of values normally used for B. cereus culture media, the cell density was significantly higher at a range greater than the recommended value [29,30]. In addition, the growth rate is observed to be a function of nutrient composition [31], uptake and utilization which is also a function of growth machinery or phase. …”