Evidence for the priming effect in single strain and simplified communities of estuarine bacteria

Through their transformation of naturally occurring organic matter, coastal marine bacteria play an essential role in carbon cycling. A phenomenon termed the priming effect (PE) occurs when microbial communities remineralize recalcitrant organic matter faster in the presence of labile organic matter and may be prevalent in coastal systems. To understand how microbial community members interact to induce PE, it is essential to first understand the mechanisms underlying PE in single strains and simplified bacterial communities. The effect to which different concentrations and sources of labile carbon stimulated the production of bacterial biomass from riverine organic matter by two marine bacteria Sagittula stellata E-37 and Citreicella sp. SE45, and a six-member, artificial community of marine bacteria that included these two strains was examined. Both strains were primed with 400μM-C acetate and 400μM-C casamino acids; however E-37 was primed with 40μM-C casamino acids, while SE45 was primed with 400μM-C tryptone. The community was primed by 400μM-C tryptone and 400μM-C coumarate. These data indicate that the magnitude and nature of PE is species-specific within the estuarine microbial community. Learning how community members contribute to a PE response will lead to a more holistic and mechanistic understanding of PE and, thereby, carbon cycling.