Background: Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such as the N-acylhomoserine lactones (AHL). These compounds are involved in the production of antibiotics, exoenzymes, virulence factors and biofilm formation. They belong to the class of furanone derivatives which are frequently found in nature as pheromones, flavor compounds or secondary metabolites. To obtain more information on the relation between molecular structure and quorum sensing, we tested a variety of natural and chemically synthesized furanones for their ability to interfere with the quorum sensing mechanism using a quantitative bioassay with Chromobacterium violaceum CV026 for antagonistic and agonistic action. We were looking at the following questions:
Biomobilization of silver, gold, and platinum from solid waste materials by HCN-forming microorganisms Biomobilization of silver, gold, and platinum from solid waste materials by HCN-forming microorganisms Abstract Cyanogenic Chromobacterium violaceum, Pseudomonas fluorescens, and P. plecoglossicida were able to mobilize silver, gold, and platinum when grown in the presence of various metalcontaining solids such as gold-containing electronic scrap, silver-containing jewelry waste, or platinum-containing automobile catalytic converters. Five percent of silver was microbially mobilized from powdered jewelry waste as dicyanoargentate after one day, although complete dissolution was obtained when non-biological cyanide leaching was applied. Dicyanoargentate inhibited growth at concentrations of >20 mg/L. Gold was bacterially solubilized from shredded printed circuit boards. Maximum dicyanoaurate concentration corresponded to 68.5% dissolution of the total gold added. Additionally, cyanide-complexed copper was detected during treatment of electronic scrap due to its high copper content of approximately 100 g/kg scrap. However, only small amounts of platinum (0.2%) were mobilized from spent automobile catalytic converter after 10 days probably due to passivation of the surface by an oxide film. In summary, all findings demonstrate the potential of microbial mobilization of metals as cyanide complex from solid materials and represent a novel type of microbial metal mobilization (termed "biocyanidation") which might find industrial application. ABSTRACT Cyanogenic Chromobacterium violaceum, Pseudomonas fluorescens, and P. plecoglossicida were able to mobilize silver, gold, and platinum when grown in the presence of various metalcontaining solids such as gold-containing electronic scrap, silver-containing jewelry waste, or platinum-containing automobile catalytic converters. Five percent of silver was microbially mobilized from powdered jewelry waste as dicyanoargentate after one day, although complete dissolution was obtained when non-biological cyanide leaching was applied. Dicyanoargentate inhibited growth at concentrations of >20 mg/L. Gold was bacterially solubilized from shredded printed circuit boards. Maximum dicyanoaurate concentration corresponded to 68.5% dissolution of the total gold added. Additionally, cyanide-complexed copper was detected during treatment of electronic scrap due to its high copper content of approximately 100 g/kg scrap. However, only small amounts of platinum (0.2%) were mobilized from spent automobile catalytic converter after 10 days probably due to passivation of the surface by an oxide film. In summary, all findings demonstrate the potential of microbial mobilization of metals as cyanide complex from solid materials and represent a novel type of microbial metal mobilization (termed "biocyanidation") which might find industrial application. Biomobilization of silver, gold, and platinum from solid waste materials by HCN-forming microorganisms
Mycobacteria possess a series of Rip peptidoglycan endopeptidases that have been characterized in various levels of detail. The RipA and RipB proteins have been extensively studied and are DL-endopeptidases, and RipA has been considered essential to Mycobacterium smegmatis and Mycobacterium tuberculosis. We show here that the ripA and ripB genes are individually dispensable in M. smegmatis and that at least one of the genes must be expressed for viability. We characterized strains carrying inframe deletion mutations of ripA and ripB and found that both mutant strains exhibited increased susceptibility to a limited number of antibiotics and to detergent but that only the ⌬ripA mutant displayed hypersusceptibility to lysozyme. We also constructed and characterized ⌬ripD and ⌬ripA ⌬ripD mutants and found that the single mutant had only an intermediate lysozyme hypersusceptibility phenotype compared to that of wild-type cells while loss of ripD in the ⌬ripA background partially rescued the antibiotic and lysozyme phenotypes of the ⌬ripA mutant. IMPORTANCEWe show that the RipA endopeptidase, which has been considered essential for cell division in certain mycobacteria, is not essential but that at least it or a similar protein, RipB, must be expressed by the bacteria for viability. This work is the first description of strains carrying single deletion mutations of RipA, RipB, and a novel endopeptidase-like protein, RipD. O ne of the most important characteristics of mycobacteria is a complex cell envelope, the biosynthesis of which is the target of several antimycobacterial drugs (1-3). Our research is focused upon the assembly and maintenance of the peptidoglycan (PG) layer, which surrounds the entirety of the cell and covalently anchors the other components of the cell envelope. The biosynthesis of the PG layer is inhibited by -lactam antibiotics, which have recently been reevaluated as potential antitubercular drugs (4, 5).The mycobacterial PG is composed of glycan strands of Nacetylglucosamine and N-acetyl/N-glycolylmuramic acid with a high degree of interpeptide cross-links (6-9). Assembly is orchestrated by a variety of transglycosylases and transpeptidases, including the penicillin binding proteins (PBPs) PonA1, PonA2, PbpA, and PbpB, as well as several LD-transpeptidases (reviewed in reference 10). In order to incorporate new precursor material into the preexisting cell wall, the old cell wall material must first be metabolized by lytic transglycosylases, endopeptidases, and amidases (11). Cell wall turnover has been extensively studied in Gram-negative bacteria, but comparatively little is known about the balance of degradation/synthesis of the PG of mycobacteria. Most of the research has focused on the Rpf resuscitation-promoting factors, which are PG glycan hydrolases, and on several PG endopeptidases (11,12).The endopeptidases belong to the NlpC/P60 superfamily (13), with the first NlpC/P60 mycobacterial proteins identified in Mycobacterium marinum and given the names iipA and iipB (invasion and ...
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