Cellular and extracellular carbohydrates and lipids from marine bacteria during growth on soluble substrates and hydrocarbons

Abstract

The variability of extracellular excretions of 4 marine bacterial strains was investigated during growth on soluble (acetate or lactate) and insoluble (hydrocarbons) substrates. Cellular and extracellular protein, carbohydrate and lipid contents were estimated at the end of exponential growth phase. Emulsifying capacity of the cell-free culture medium was estimated. Lipid classes were charac-terized by using thin layer chromatography coupled with flame ionization detection. All strains were found to excrete organic compounds in their culture medium whatever the substrate. Carbohydrate and lipid compounds were the main products whereas proteins were excreted in lesser amounts. Neverthe-less, the adaptation of the marine strains to insoluble substrate was characterized by enhanced lipid excretions (mainly phospholipids) which correlated well with higher emulsifying activity on this substrate. These excretions represented 8.6 to 156.2 and 4.3 to 101.6 yg per mg bacterial carbon, for carbohydrates and lipids respectively, according to a recent estimate of the bacterial protein to carbon ratio. These data show that inputs of dissolved organic compounds through bacterial activity could have important consequences on the physico-chemical characteristics of seawater in area where bacterial biomass is concentrated.