Increased bacterial growth efficiency with environmental variability: results from DOC degradation by bacteria in pure culture experiments

Abstract

Abstract. This paper assesses how considering variation in DOC availability and cell maintenance in bacterial models affects Bacterial Growth Efficiency (BGE) estimations. For this purpose, we conducted two biodegradation experiments simultaneously. In experiment one, a given amount of substrate was added to the culture at the start of the experiment whilst in experiment two, the same amount of substrate was added, but using periodic pulses over the time course of the experiment. Three bacterial models, with different levels of complexity, (the Monod, Marr-Pirt and the dynamic energy budget (DEB) model), were used, and calibrated using the above experiments. BGE has been estimated using the experimental values obtained from discrete samples and from model generated data. Cell maintenance was derived experimentally, from respiration rate measurements. The results showed that the Monod model did not reproduce the experimental data accurately, whereas the Marr-Pirt and DEB models demonstrated a good level of reproducibility, probably because cell maintenance was built into their formula. Whatever estimation method was used, the BGE value was always higher in experiment two (the periodically pulsed substrate) as compared to the initially one-pulsed-substrate experiment. Moreover, BGE values estimated without considering cell maintenance (Monod model and empirical formula) were always smaller than BGE values obtained from models taking cell maintenance into account. Since BGE is commonly estimated using constant experimental systems and ignore maintenance, we conclude that these typical methods underestimate BGE values. On a larger scale, and for biogeochemical cycles, this would lead to the conclusion that, for a given DOC supply rate and a given DOC consumption rate, these BGE estimation methods overestimate the role of bacterioplankton as CO2 producers.

Organic carbon dynamics in the Mediterranean Sea: An integrated study

“…Bacterial carbon demand (BCD) was calculated from the BP with a unique bacterial growth efficiency (BGE) of 15%, as reported for the Sargasso Sea [ Carlson and Ducklow , 1996] and for the west Med [ Sempéré et al , 2003]. This value can be criticized because bacteria, which originate from different stations and depths, very likely grow with different BGE [ Eichinger et al , 2006, 2010, 2011]. The 15% value was used to obtain a rough estimate of the average amount of DOC needed by bacteria to sustain the observed BP.…”

A universal bacterial inoculum for dissolved organic carbon biodegradation experiments in freshwaters

“…Finally, it would allow for a consistent chemical signature from the community on the DOC samples and ideally a common exometabolome (Wienhausen et al ). Past studies have successfully used single bacterial isolates to answer research questions about the drivers of DOC biodegradation, such as the effects of labile C additions (Bianchi et al ) or environmental variability (Eichinger et al ). Indeed, single or reduced groups of bacterial strains seem able to consume most of the labile DOC pool in aquatic ecosystems (Nelson and Wear ; Pedler et al ).…”

The AquaDEB project: Physiological flexibility of aquatic animals analysed with a generic dynamic energy budget model (phase II)

“…Where predation-prey interactions dominate the literature on population dynamics, our results point to the importance of syntrophic interaction as one of the mechanisms for maintenance of biodiversity (Muller et al, 2009;Eynaud et al, 2011). Nutritional details and the dynamics of biodegradation can have large effects on system properties (Eichinger et al, 2009(Eichinger et al, , 2010Poggiale et al, 2010), a worrying observation.…”

“…A strong effect of a chemical compound is less of a problem if combined with a very short residence time in the environment; the degradability of compounds (e.g. Lika and Papadakis, 2009;Eichinger et al, 2010) is of more environmental relevance then its effects, but the combination is what matters. Extrapolation from effects of one compound to that of the other, form effects on one species to other species of organism, from effects on individuals to that on populations and ecosystems will need to be integrated with effect-fate studies.…”