Coupling between bacterioplankton species composition, population dynamics, and organic matter degradation

Abstract

To study the effect of substrate addition on short term bactenal population dynamics and species composltion in seawater mesocosms were maintained u l t h water collected off Scnpps Pler (La Jolla Callfornla USA) Protein enrichment (BSA) triggered a dynamlc response from the microbial food web, whereas ennchment with starch had no effect In the proteln enriched mesocosm the number of both nucleold-contain~ng cells and metabolically active cells increased by 3 0 X 105 cells ml-' from Day 1 to Day 4 In the same time period the density of a set of 31 phylogenetically different bactena (ccand y-Proteobactena as well as Flexibacter-Cytophaga-Bacteroides) increased by 3 5 X 105 cells ml-' The abundance of these isolated bactena accounted for up to 8 9 % of the nucleoid-conta~ning cells, and up to 2 2 % of the total counts Increased enzyme activities most notably protease, were found conconutant with a change in bactenal species composltion over 3 d This short term succession was possible due to rapid net growth rates of slngle bactenal species in the mesocosm (0 48 to 1 6 d-l), which was up to 5 times hlgher than the community turnover calculated from bactenal production and total counts These results should provide support for studles of actual bactenal population dynamics on the species level and its role in the degradation of organic matter in the aquatic environment