MEPS prepress abstract  -  DOI:

Production and consumption of extracellular polymeric substances in an intertidal diatom mat

Tanja C. W. Moerdijk-Poortvliet, Olivier Beauchard, Lucas J. Stal, Henricus T. S. Boschker


ABSTRACT: The seasonal changes in the production of extracellular polymeric substances (EPS) and short chain organic acids (SCOA) exuded by benthic diatoms and the use of these exudates as a carbon source by heterotrophic bacteria were investigated. An in-situ 13C pulse-chase method was used to follow the fate of EPS for 5 consecutive days. These experiments were done at 2-month intervals for 1 year. The EPS were recovered from the sediment as 2 operational defined fractions (i.e. water-extractable and EDTA-extractable EPS). The seasonal differences of EPS production correlated to light intensity and temperature. From February until June the biomass and production of diatoms and bacteria were closely coupled. It was concluded that SCOA were the most important substrates for the bacteria. Especially sulfate-reducing bacteria (SRB) benefited from SCOA released by diatoms. From August on, the coupling of biomass and production of diatoms and bacteria became less strong and was almost lost in December. During the period August to December, EPS produced by diatoms promoted the growth of other bacterial taxa rather than SRB, and the production of SCOA was low. The seasonal variation in exudates produced by diatoms therefore played an important role in shaping the community composition and maintaining the diversity of the associated bacteria.