Single bacterial strain capable of significant contribution to carbon cycling in the surface ocean

Abstract

Marine dissolved organic carbon (DOC) encompasses one of the largest reservoirs of carbon on Earth. Heterotrophic bacteria are the primary biotic force regulating the fate of this material, yet the capacity of individual strains to significantly contribute to carbon cycling is unknown. Here we quantified the ability of a single Alteromonas strain [Alteromonas sp. strain Scripps Institution of Oceanography (AltSIO)] to drawdown ambient DOC in a coastal ecosystem. In three experiments, AltSIO alone consumed the entire pool of labile DOC, defined here as the quantity consumed by the submicron size fraction of ambient microbial assemblages within 5 d. These findings demonstrate that complete removal of the labile DOC pool in coastal surface seawater can be achieved by a single taxon. During long-term incubations (>1 y) testing semilabile DOC consumption, AltSIO entered dormancy but remained viable, while the diverse assemblages continued to consume carbon. Given that AltSIO is a large bacterium and thus subject to increased grazing pressure, we sought to determine the ecological relevance of this phenotype. Growth dynamics in natural seawater revealed that AltSIO rapidly outgrew the native bacteria, and despite intense grazing pressure, was never eliminated from the population. A survey in the California Current Ecosystem revealed that large bacteria (≥40 fg C·cell −1 ) were persistent, accounting for up to 12% of total bacterial abundance and 24% of total bacterial biomass. We conclude that large, rapidly growing bacteria have the potential to disproportionately alter the fate of carbon in the mesotrophic ocean and play an important role in ecosystem function.dissolved organic matter | ocean carbon cycle | marine biogeochemistry | microbial loop | CCE

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

“…This may be attributable to the fact that reduced resource diversity and variable supply, as typical for highaltitudinal streams (Battin et al, 2004;Milner et al, 2009), may prevent microorganisms from specialising on a few carbon sources. This observation is in line with recent reports on marine microorganisms showing a low degree of specialisation on carbon sources (Mou et al, 2008;Pedler et al, 2014).…”

Experimental demonstration of an Allee effect in microbial populations

“…The strength of the effect, represented by the critical density, increased with predation and decreasing carbon ( figure 1). Possibly, even more pronounced Allee effects would be observed in natural marine populations of heterotrophic bacteria where natural concentrations of dissolved organic carbon are up to three orders of magnitude lower than in our experiments [14]. V. fischeri populations subject to C. roenbergensis predation at natural concentrations [15] had a significantly higher critical threshold than populations without predation.…”

Transcriptional response of Prochlorococcus to co-culture with a marine Alteromonas: differences between strains and the involvement of putative infochemicals

“…Alteromonas are typically not very common in the oceans (Eilers et al, 2000) yet are often identified in rRNA-based analyses of microbial communities in open water, and thus naturally co-occur with Prochlorococcus (García- Martínez et al, 2002;Ivars-Martinez et al, 2008;Lopez-Perez et al, 2012). They are metabolically-versatile copiotrophs (Pedler et al, 2014), rapidly responding to increases in dissolved organic matter and often dominating mesocosm experiments (McCarren et al, 2010). Several Alteromonas strains have been shown to inhibit eukaryotic phytoplankton such as diatoms, dinoflagellates and raphidophytes (reviewed by Mayali and Azam, 2004).…”