Abstract
The concentration of atmospheric carbon dioxide is directly linked to the sinking of photosynthetically derived particulate organic carbon (POC) from surface waters to deep waters. This process, known as the marine biological carbon pump, removes carbon from exchange with the atmosphere, thus regulating global climate. Recent evidence suggests that microbial chemical communication systems (e.g. quorum sensing) amongst heterotrophic bacteria associated with sinking POC, significantly influences their hydrolytic enzyme activity and, as such, may affect the efficiency of the biological carbon pump. Here, we present data showing that a class of quorum sensing molecules, acylated homeserine lactones (AHLs) substantially impact hydrolytic phosphatase, aminopeptidase, and lipase activity in samples of sinking particles collected from the Atlantic and Pacific Ocean. Incubations of sinking particles amended with exogenous AHLs showed both stimulated and inhibited rates of activity after 24 hours of incubation, suggesting a critical link between bacterial AHL signaling mechanisms and the rate of POC degradation. Further experiments reveal that hydrolytic pathways could be affected within a few hours of amendment with AHLs, suggesting that microbial communities are able to dynamically modify their metabolic pathways in response to perceived quorum sensing. Finally, the concentration of the AHL amendment also affected hydrolytic activity. Our results indicated that quorum sensing has the potential to influence hydrolytic activity in a range of oceanic environments, but response also vary significantly as a function of the type of AHL, their concentration, and response time. AHL-based quorum sensing may be thought of as a global language among marine bacteria, but it is highly complex.
Highlights
Oceanic carbon export via sinking particles plays a pivotal role in regulating Earth’s climate
We examined geographic variability in the effects of two classes of acylated homeserine lactones (AHLs) on three bacterial enzyme activities from samples of sinking particles collected at five locations across the Pacific Ocean and the Atlantic Ocean (Figure 1)
Of the 87 separate comparisons of average enzyme activities in incubations amended with AHLs, 26 showed rates that were statistically different than the no-amendment control incubations, indicating a response of particle-associated bacteria to AHLs
Summary
Oceanic carbon export via sinking particles plays a pivotal role in regulating Earth’s climate. Photosynthetic microorganisms (e.g., phytoplankton) in the marine environment convert atmospheric CO2 into biomass; the majority of this organic carbon is recycled in surface waters by diverse microbial processes. Some of this biomass sinks as particulate organic carbon (POC) into deeper regions of the ocean via the biological carbon pump, where bacterial cells continue to play a critical role in regulating the efficiency of carbon export through the colonization and enzymatic hydrolysis of sinking particles (Turley and Mackie, 1994; Simon et al, 2002). Far, our knowledge about the potential importance of bacterial quorum sensing on sinking particles is limited because only a few cultivation–independent studies have been carried out in the marine environment (Decho et al, 2009; Van Mooy et al, 2012; Ransome et al, 2014; Zimmer et al, 2014; Certner and Vollmer, 2015)
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