Contribution of photosynthetic sulfur bacteria to the alkaline phosphatase activity in anoxic aquatic ecosystems

Abstract

We studied the relationship between photosynthetic sulfur bacteria and the amount and distribution of alkaline phosphatases in 2 small lakes in the Banyoles (NE Spain) karstic complex. The maximum alkaline phosphatase activity (APA) was found in the oxic/anoxic boundary layer (over 40 μM pNP [p-nitrophenol] h-1). Multiple regression analysis of environmental data revealed a high correlation between bacterial pigments and particulate APA. A correlation coefficient (r2) of 0.550 was found in Lake Vilar when bacteriochlorophyll (Bchl) a was used as an independent variable. For Lake Siso, the best correlation (r2 = 0.577) was obtained when Bchl e, Bchl d and chl a were used as independent variables. The specific alkaline phosphatase activities (SAPA) in the oxic layers were strongly influenced by the presence of photosynthetic bacteria. The induction of APA by 3 strains of photosynthetic bacteria isolated from the lakes was tested in the laboratory by measuring the response to incubation with different sources of organic phosphorus. Chromatium minus UdG2026, Chlorobium phaeobacteroides UdG6054 and Chlorobium limicola UdG6040 significantly increased the APA when incubated under phosphate limitation.