NUTRITIONAL ENRICHMENT OF A MICROBIAL COMMUNITY - THE EFFECTS ON ACTIVITY, ELEMENTAL COMPOSITION, COMMUNITY STRUCTURE AND VIRUS PRODUCTION

Viruses are active members of the microbial community in natural water s but little is known about the factors that regulate their activity a nd production. In this study we have investigated the effects of incre ased availability of organic nutrients and inorganic phosphate on acti vity, elemental composition, community structure and virus production in a natural bacterial community. The fraction of active cells in the community as estimated from microautoradiography of cells assimilating H-3-labeled thymidine ranged from 0-22%, but changes in the elemental composition of the cells indicated that more than 90% of the cells we re active. The increase in carbon and energy availability stimulated v irus production more than bacterial biomass production, while the incr ease in phosphate availability stimulated biomass production rather th an virus production. A decrease in morphological diversity of the bact erial community was paralleled by a reduction in the virus-to-bacteria ratio (VER) but the relationship between bacterial diversity and vira l activity is uncertain. Our general conclusion is that nutrient avail ability, in addition to the bacterial activity, also affects the viral activity, and that both of these may affect the structure and diversi ty of the bacterial community.