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

We studied the relationship between photosynthetic sulfur bacteria and the amount and distribution of alkaline phosphatases in 2 small lakes in the Ba nyoles (NE Spain) karstic complex. The maximum alkaline phosphatase activit y (APA) was found in the oxic/anoxic boundary layer (over 40 mu M pNP [p-ni trophenol] h(-1)). Multiple regression analysis of environmental data revea led a high correlation between bacterial pigments and particulate APA. A co rrelation coefficient (r(2)) of 0.550 was found in Lake Vilar when bacterio chlorophyll (Bchl) a was used as an independent variable. For Lake Siso, th e best correlation (r(2) = 0.577) was obtained when Bchl e, Bchl d and chi a were used as independent variables. The specific alkaline phosphatase act ivities (SAPA) in the oxic layers were strongly influenced by the presence of photosynthetic bacteria. The induction of APA by 3 strains of photosynth etic bacteria isolated from the lakes was tested in the laboratory by measu ring the response to incubation with different sources of organic phosphoru s. Chromatium minus UdG2026, Chlorobium phaeobacteroides UdG6054 and Chloro bium Limicola UdG6040 significantly increased the APA when incubated under phosphate limitation.