Production of two phosphatases by a Citrobacter sp. grown in batch and continuous culture

Acid phosphatase was recovered from biomass of a Citrobacter sp. in two iso forms designated as CPI and CPII. Although similar, the enzymes had differe nt stability properties which would relate to their suitability for biotech nological processes to remove heavy metals via enzymatically mediated preci pitation as insoluble metal phosphates. The proportions of CPI and CPII ext racted varied according to the Citrobacter strain and growth regime. Enzyme overproduction (mainly as CPII) used high-activity cells grown in batch cu lture whereas use of glycerol-limiting continuous culture gave initially ma inly CPI and Inter predominantly CPII. This change corresponded to a fall i n the total specific activity from 2,000-3.000 units to less than 600 units Initial batch studies showed increased phosphatase production where growth was limited by the degree of aeration. Further tests using carbon-limiting continuous culture suggested that the total enzyme activity was influenced by a combination of the dissolved oxygen concentration and the pH. These o bservations are consistent with a multifactorial regulation of the acid pho sphatase gene phoN by the PhoP/PhoQ sensor/regulator system which is known to govern responses to stress in the related organism Salmonella typhimuriu m (C) 1998 Elsevier Science Inc.