AME 62:267-277 (2011)  -  DOI: https://doi.org/10.3354/ame01469

ABSTRACT: We examined the incorporation of leucine, protein, and a mixture of 15 amino acids by selected phylogenetic groups in light and dark incubations of coastal waters of the Delaware Bay and Mid-Atlantic Bight. In experiments conducted over 3 yr, the single-cell activity of different groups of bacteria varied with molecular weight of the substrate, photosynthetically active radiation (PAR), and other environmental conditions. The fraction of cells active in using leucine and incorporating protein differed among groups and between summer and fall. About 30% of all cells incorporated the amino acid mixture, while only 10% incorporated protein. PAR availability affected single-cell activity in 20% of all experiments, and PAR conditions prior to sampling correlated with light effects on single-cell activity, varying with the compound (amino acid mixture, leucine or protein). The bacterial group most consistently affected by PAR was the SAR11 clade; 25% more SAR11 bacteria used leucine in the light than the total community. The study illustrates the complex effects of light on single-cell activity of bacterial groups and helps to explain the variability in the impact of light on dissolved organic carbon fluxes.

KEY WORDS: Microautoradiography · Bacterial activity · Light · DOM incorporation