Effects of d-Amino Acids on the EPS Production and Cell Aggregation of Alteromonas macleodii Strain JL2069

Exopolysaccharide (EPS) is produced by many marine bacteria and is important for cell aggregation in the ocean. d-amino acids are important components in bacteria and are recently recognized as signal molecules for regulation of bacterial growth. In this study, the effects of d-amino acids on EPS production, cell aggregation, and metabolic activity were investigated using an EPS-producing bacterium Alteromonas macleodii strain JL2069. EPS produced by JL2069 was inhibited by 1 mM of d-Ala and d-Ser, but not by d-Glu. The formation of particulate organic matter (POM) was promoted by the three amino acids. A new technique of microcalorimetry analysis indicated that the metabolic activity of the JL2069 cells was inhibited by these d-amino acids. Our results suggested that d-amino acids may reduce the bacterial metabolism by changing bacterial lifestyle from planktonic to cell aggregation growth which occurs independent of the production of EPS.