IMPACT OF A GENETICALLY-ENGINEERED BACTERIUM WITH ENHANCED ALKALINE-PHOSPHATASE ACTIVITY ON MARINE-PHYTOPLANKTON COMMUNITIES

An indigenous marine Achromobacter sp, was isolated from coastal Georg ia seawater and modified in tile laboratory by introduction of a plasm id with a phoA hybrid gene that directed constitutive overproduction o f alkaline phosphatase, The effects of this ''indigenous'' genetically engineered microorganism (GEM) on phosphorus cycling were determined in seawater microcosms following the addition of a model dissolved org anic phosphorus compound, glycerol 3-phosphate, at a concentration of 1 or 10 mu M. Within 48 h, a 2- to 10-fold increase in the concentrati on of inorganic phosphate occurred in microcosms containing the GEM (a dded at an initial density equivalent to 8% of the total bacterial pop ulation) relative to controls containing only natural microbial popula tions, natural populations with the unmodified Achromobacter sp,, or n atural populations with the Achromobacter sp. containing the plasmid b ut not the phoA gene, Secondary effects of the GEM on the phytoplankto n community were observed after several days, evident as sustained inc reases in phytoplankton biomass (up to 14-fold) over that in controls, Even in the absence of added glycerol 3-phosphate, a numerically stab le GEM population (averaging 3 to 5% of culturable bacteria) was estab lished within 2 to 3 weeks of introduction into seawater. Moreover, al kaline phosphatase activity in microcosms with the GEM was substantial ly higher than that in controls for up to 25 days, and microcosms cont aining the GEM maintained the potential for net phosphate accumulation above control levels for longer than 1 month.