11/19/2023 0 Comments 3 pb precipitate color![]() The one instance in which PbS precipitation has been suggested was a Klebsiella strain cultured in phosphate-limited medium ( 5). ( 30) suggested that Pb 3(PO 4) 2 is the precipitate produced by S. ( 4) identified the precipitate produced by a Citrobacter sp. The precipitate produced by Pseudomonas fluorescens is known to contain lead and phosphorus, but the stoichiometry has not been reported ( 6). Formation of the precipitate does not seem to be associated with a decrease in the growth rate ( 2).ĭetailed analyses of microbially precipitated lead compounds are rare. One study in which Staphylococcus aureus was examined demonstrated that lead precipitation occurred in both lead-sensitive and lead-resistant strains however the resistant strains were more effective at expulsion ( 30). Both phosphate-replete and phosphate-starved Pseudomonas cultures generate an insoluble material containing both lead and phosphorus, although phosphate-replete cultures are apparently more efficient at expelling the material ( 6). A number of studies have shown that various bacterial strains sequester lead intracellularly ( 2, 4, 5, 6, 30, 36, 38, 52), and some of these studies have demonstrated that the lead is localized to the cell membrane or the cell surface ( 4, 5, 30, 38, 52). The second mechanism appears to be precipitation of the lead in an insoluble form. The first of these mechanisms is an active efflux mechanism ( 14, 37, 43), a frequent resistance strategy employed by bacteria against heavy metals (for a review, see reference 44). Studies of prokaryotic tolerance and resistance to soluble lead have revealed two general mechanisms. harveyi carries at least one quorum sensor that is specifically dedicated to receiving cross-species communication. Based on these observations, we propose that V. harveyi inocula but was quite responsive to some of the heterologous bacteria. harveyi mutants in this study exhibited little or no response to intercellular signals from other V. Experiments with heterologous bacterial populations demonstrated that many different species are capable of trans regulating the V. harveyi autoinducer, referred to as AI3, can also negatively regulate lead precipitation. This suggests that a previously undescribed V. harveyi D1 mutant, a strain defective for secretion of both AI1 and AI2, was shown to be an effective trans inhibitor of lead precipitation. Introduction of a luxO:: kan allele into one of the mutants abolished lead precipitation, indicating that the well-characterized autoinducer 1 (AI1)-AI2 quorum-sensing system can block lead precipitation in dense cell populations. Regulation of the precipitation phenotype was also examined. These assays identified the precipitated compound as Pb 9(PO 4) 6, an unusual and complex lead phosphate salt that is produced synthetically at temperatures of ca. ![]() The compound was purified and subjected to X-ray diffraction and elemental analyses. Three pleiotropic, quorum sensing-defective Vibrio harveyi mutants were observed to precipitate soluble Pb 2+ as an insoluble compound.
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