title: Phosphatase production and activity in Citrobacter freundii and a naturally occurring, heavy-metal-accumulating Citrobacter sp.
abstract: The ability of a naturally occurring Citrobacter sp. to accumulate cadmium has been attributed to cellular precipitation of CdHPO4, utilizing HPO4(2-) liberated via the activity of an overproduced, Cd-resistant acid-type phosphatase. Phosphatase production and heavy metal accumulation by batch cultures of this strain (N14) and a phosphatase-deficient mutant were compared with two reference strains of Citrobacter freundii. Only strain N14 expressed a high level of acid phosphatase and accumulated lanthanum and uranyl ion enzymically. Acid phosphatase is regulated via carbon-starvation; although the C. freundii strains overexpressed phosphatase activity in carbon-limiting continuous culture, this was approximately 20-fold less than the activity of strain N14 grown similarly. Citrobacter strain N14 was originally isolated from a metal-contaminated soil environment; phosphatase overproduction and metal accumulation were postulated as a detoxification mechanism. However, application of Cd-stress, and enrichment for Cd-resistant C. freundii ('training'), reduced the phosphatase activity of this organism by about 50% as compared to Cd-unstressed cultures. The acid phosphatase of C. freundii and Citrobacter N14 had a similar pattern of resistance to some diagnostic reagents. The enzyme of the latter is similar to the PhoN acid phosphatase of Salmonella typhimurium described by other workers; the results are discussed with respect to the known phosphatases of the enterobacteria.
authors.affiliation: Physical Chemistry Laboratory, University of Oxford, UK.
authors.forename: D M
authors.initials: DM
authors.lastname: Montgomery
authors.forename: A C
authors.initials: AC
authors.lastname: Dean
authors.forename: P
authors.initials: P
authors.lastname: Wiffen
authors.forename: L E
authors.initials: LE
authors.lastname: Macaskie
mesh_terms: D000135:Acid Phosphatase / Q000096:biosynthesis* / Q000187:drug effects; D002104:Cadmium / Q000378:metabolism / Q000494:pharmacology; D016971:Citrobacter freundii / Q000201:enzymology* / Q000378:metabolism; D004352:Drug Resistance, Microbial; D015971:Gene Expression Regulation, Enzymologic; D008658:Inactivation, Metabolic; D007811:Lanthanum / Q000378:metabolism; D008670:Metals / Q000378:metabolism*; D013045:Species Specificity; D017974:Uranium Compounds / Q000378:metabolism
chemical_list: D008670:Metals; D017974:Uranium Compounds; D002104:Cadmium; D007811:Lanthanum; D000135:Acid Phosphatase