Discrimination of algal and bacterial alkaline phosphatases with a differential-inhibition technique

Murray-Darling Freshwater Research CentreMDFRC item.Both phytoplankton and bacterioplankton produce alkaline phosphatases, but the techniques currently available for discriminating between the two sources are poor, especially when samples are from turbid waters. A novel approach, based on the differential inhibition of alkaline phosphatases by various physical and chemical treatments, was assessed as a rapid and inexpensive technique for determining whether phytoplankton or bacterioplankton were the more important producers of alkaline phosphatases in turbid rivers of south-eastern Australia. Eight phytoplankton strains and 14 bacterial strains (eight isolated from the Ovens River and six isolated as bacterial contaminants of the phytoplankton cultures) were grown in laboratory culture. Rates of alkaline phosphatase activity in the bacterial cultures varied from 70% of cases) grouped separately from those of the laboratory cultures of bacteria and phytoplankton, perhaps because the microbes studied in laboratory culture were not representative of native assemblages or because the culture conditions did not mimic those in nature. Nevertheless, differential-inhibition techniques have much potential for determining the origin of the alkaline phosphatases found in natural waters, with the major factor limiting their application being the collection of valid inhibition profiles for native bacterial and algal communities.