Bacterioplankton growth on extracellular organic carbon from marine microalgal cultures

Abstract

Marine bacterial growth on extracellular organic carbon (EOC) of Chlorella minutissima, Dimaliella tertiolecta and Chaetoceros gracilis was studied. EOC was retrieved after filtration of optimum growing algal cultures at the middle of the exponential growth phase and the stationary phase. The filtrates were inoculated with natural marine bacterial assemblages. The batch cultures were monitored for dissolved organic carbon (DOC) concentrations, bacterial yield, biomass and oxygen respiration over a period 3.5-10 days. The overall bacterial response was statistically different between the algal species origin of EOC and between the two growth phases for each species. These differences were also found for DOC normalised values suggesting that they were due to qualitative differences of the EOC. The highest bacterial yield was induced by the EOC originating from D. tertiolecta and the lowest by the C. minutissinia EOC. Oxygen respiration followed the same pattern with significantly higher values in the cultures with D. tertiolecta and C. gracilis stationary phase EOC. DOC degradation rate, utilisable DOC, bacterial growth rate and bacterial growth efficiency was different between the EOC from the exponential and stationary phase of algal growth, only in the case of C. gracilis. Of all the algal species studied here, it seems that the exponential C. gracilis EOC is more labile for marine bacteria.