Inter-Research
Aquatic Microbial Ecology

ABSTRACT: Microbial degradation of Phaeocystisglobosa colonies and their derived organic matter by free-living and attached bacteria was investigated in Belgian coastal waters during the spring development of diatom-Phaeocystis colonies in 1994. Results obtained show concomitant evolution of hydrolytic ectoprotease and b-ectoglucosidase ectoenzymatic activities with respect to the phytoplankton bloom, suggesting that the low biodegradability of Phaeocystis colonies leading to transient accumulations of Phaeocystis-derived material in the coastal North Sea was not due to a lag phase required for the induction of b-ectoglucosidase. Up to 66% of total bacterial biomass was found attached to particles larger than 10 µm. While occurring always in low abundance compared to free-living bacteria, both the average specific biomass and growth rate of particle-attached bacteria were very high, i.e. 60 fg C cell^-1 and 0.28 h^-1, respectively. Similarly, specific ectoenzymatic activities of particle-attached bacteria were on average about 5 times higher than those characterising free-living bacteria. Budget calculations show a 53% contribution of Phaeocystis-attached bacteria to the mineralisation of Phaeocystis-associated production, i.e. a 53:47% role for attached and free-living bacteria, respectively.

KEY WORDS: Phaeocystis degradation · Free-living and particle-attached bacteria · Ectoenzymatic activity · Growth rate

Published in AME Vol. 14, No. 1 (1998) on January 2
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 1998