DEGRADATION BY BACTERIA OF MEMBRANE AND SOLUBLE-PROTEIN IN SEAWATER

In order to test the hypothesis that bacterial membrane protein is mor e slowly degraded than soluble protein in seawater, we examined degrad ation by natural bacterioplankton of membrane and soluble proteins pre pared from the marine bacterium Vibrio alginolyticus radiolabeled with H-3- or C-14-leucine. First order kinetic constants indicated that pr oteins in crude membrane extract are degraded at significantly slower rates (1/2 to 1/6) than the soluble proteins. Proteins determined to b e intimately associated with the membrane were not degraded during the initial 45 hi while a substantial fraction of soluble proteins was de graded during the same period. The data are consistent with a model in which membrane and cell wall materials severely restrict access of ba cterial proteases to membrane proteins. After prolonged incubation, ho wever, membrane proteins started to be degraded, suggesting that prote ins protected by membrane components were made available for degradati on after ectoenzymatic destruction of membrane components. Our data su pport the hypothesis that macromolecular organic complexes play a role in temporary storage of dissolved organic matter (DOM) in seawater an d that complementary hydrolysis by different ectoenzymes produced by d iverse bacterioplankton is important in determining rates and patterns of DOM degradation in the sea.