Bacterial contributions to formation of transparent exopolymer particles (TEP) and seasonal trends in coastal waters of Sagami Bay, Japan

Abstract

Seasonal trends in the bacterial formation of transparent exopolymer particles (TEP) were assessed in a seawater culture experiment using filtrate (0.8 μm) obtained from surface water of Sagami Bay, Japan. An Alcian blue staining/colorimetric method was used to assess samples in both the presence and absence of metabolic inhibitors of bacteria. TEP formation was always negligible in the presence of metabolic inhibitors. However, the TEP accumulation rate (t = 0 to 1) associated with bacterial growth was high (156.9 ± 66 μg Gum Xanthan equivalents l-1 d-1) in September, October, and March, and low (0 ± 12.7 μg Gum Xanthan equiv. l-1 d-1) from December to February, even for samples with large increases in bacterial numbers. The observed TEP accumulation rate without metabolic inhibitors was positively correlated with chlorophyll a concentration (r = 0.799, n = 9), bacterial organic carbon production rate (r = 0.784, n = 9), and bacterial number (r = 0.948, n = 9) in the field, indicating the importance of exudates from phytoplankton and probably from bacteria. During the months with high TEP formation rates, the bacterial TEP that formed in terms of carbon exceeded bacterial carbon utilization by 1- to 2-fold, suggesting an indirect process of bacterial TEP formation. Based on microscopic examinations of seawater cultures and field samples, the scavenging of TEP precursors by increased bacterial particles was important in the bacterial enhancement of high TEP formation in fall and early spring. These observations suggest the importance of bacteria as mediators of bacteria-associated TEP formation coupled to the supply of usable dissolved organic matter, including TEP precursors. © Inter-Research 2007.