Production of exopolymer particles by marine bacterioplankton under contrasting turbulence conditions

It has recently been shown that marine bacterioplankton release copious amounts of capsular material as 'semi-labile' to 'refractory' dissolved organic carbon (DOC) into the ambient water. The fate of this bacterioplankton-derived DOC remains largely unknown. Here we investigate the capability of this bacterial-derived capsular DOC to coagulate to exopolymer particles under contrasting turbulence regimes. Under high turbulence, fewer but larger particles (>2 mu m in diameter) were detected, while the total exopolymer particle-mass (>0.2 mu m) was higher under stagnant conditions. Under stagnant conditions most of the bacterial-derived particles remained in the size-class between 0.2 and 2 mu m. The production rate of exopolymer particles was estimated to amount to about 4 amol C cell(-1) h(-1), representing about 25% of the previously estimated bacterioplankton DOC release of about 15 amol C cell(-1) h(-1). Considering that bacterioplankton represent the largest living surface in the ocean, the release and subsequent coagulation of bacteriopIankton-derived capsular DOC might be an important. thus far largely neglected mechanism of exopolymer particle formation in the ocean.