Temperature dependences of growth rates and carrying capacities of marine bacteria depart from metabolic theoretical predictions

Abstract

Using the metabolic theory of ecology (MTE) framework, we evaluated over a whole annual cycle the monthly responses to temperature of the growth rates (μ) and carrying capacities (K) of heterotrophic bacterioplankton at a temperate coastal site. We used experimental incubations spanning 6ºC with bacterial physiological groups identified by flow cytometry according to membrane integrity (live), nucleic acid content (HNA and LNA) and respiratory activity (CTC+). The temperature dependence of μ at the exponential phase of growth was summarized by the activation energy (E), which was variable (-0.52 to 0.72 eV) but followed a seasonal pattern, only reaching the hypothesized value for aerobic heterotrophs of 0.65 eV during the spring bloom for the most active bacterial groups (live, HNA, CTC+). K (i.e. maximum experimental abundance) peaked at 4 × 10(6) cells mL(-1) and generally covaried with μ but, contrary to MTE predictions, it did not decrease consistently with temperature. In the case of live cells, the responses of μ and K to temperature were positively correlated and related to seasonal changes in substrate availability, indicating that the responses of bacteria to warming are far from homogeneous and poorly explained by MTE at our site.

Temperature regulation of marine heterotrophic prokaryotes increases latitudinally as a breach between bottom‐up and top‐down controls

“…Similar to the annual variability found in a temperate ecosystem (Huete‐Stauffer et al. , Calvo‐Díaz et al., ), we interpret the inverse temperature control versus bottom‐up control relationship as a relief of resource availability stress. That is, when dissolved organic matter is no longer limiting, prokaryotes will not respond to further increases in substrate inputs and then temperature takes the rule in the expected way, that is warming results in increased metabolic activity due to acceleration of the cellular enzymatic machinery.…”

“…The mean E obtained in this study was more than twice the mean value assumed for heterotrophic organisms (0.65 eV, Gillooly, Brown, West, Savage, & Charnov, ). Recent experimental work on the activation energy of the specific growth rates of heterotrophic prokaryotes has shown that E can vary widely on a seasonal scale with low values in periods of nutrient limitation (Huete‐Stauffer, Arandia‐Gorostidi, Díaz‐Pérez, & Morán, ). Spatially, higher E values are usually found in cold environments (Mazuecos et al., ; Vaquer‐Sunyer, Duarte, Santiago, Wassmann, & Reigstad, ).…”

Testing the metabolic theory of ecology with marine bacteria: different temperature sensitivity of major phylogenetic groups during the spring phytoplankton bloom

“…However, the metabolic response of widespread phylogenetic groups of marine bacteria to ocean warming is largely unknown. In a companion paper assessing the temperature‐dependence of heterotrophic bacteria growth rates from a community level perspective, a high temporal variability was found (Huete‐Stauffer et al ., ). A plausible explanation for this finding was that distinct bacterial groups dominating different periods of the year exhibited different temperature‐responses, an idea that, to our knowledge, has been never tested in a complete annual cycle.…”

“…Since temperature governs enzyme kinetics (Elias et al ., ), ocean warming is expected to have a generalized, direct impact on variables related to metabolism (Gillooly et al ., ; Kingsolver and Huey, ; O'Connor et al ., ; Huete‐Stauffer et al ., ; Morán et al ., ). However, we report here large discrepancies with the MTE predictions of four widespread phylogenetic groups of coastal bacterioplankton.…”

“…However, such universal values of the exponent have been questioned (Glazier, ), and due to the small size variability of bacteria (usually less than 0.01 µm 3 ) we did not perform any mass‐correction as discussed by Huete‐Stauffer et al . ().…”