Bacteria metal-binding

Few studies have evaluated the potential for use of microorganisms in the remediation of sea water however, the problems encountered are similar to those of other aquatic systems. Stupakova et al. (1988) proposed the use of the marine bacteria Deleya venustus and Moraxella sp. for copper uptake from sea water. Additionally, Corpe (1975) performed metal-binding studies with copper using exopolymer from film-producing marine bacteria and found that insoluble copper precipitates formed, effectively decreasing copper toxicity. 

Corpe, W. A. (1975). Metal-binding properties of surface material from marine bacteria. Developments in Industrial Microbiology, 16, 249-55. 

Surprisingly, too, there are claims of higher oxidation states of Mn in some systems, e.g. Mnlv in photosynthetic(II) chloroplast systems and Mn111 in acid phosphatase. In the latter enzyme Tyr and Cys residues appear to form part of the metal-binding site. The metal is also involved in the phosphate binding. While superoxide dismutase (SOD) is more generally found with Cu and Zn as the active metals, an Mn-SOD form is found in certain bacteria. The Mn oscillates between different oxidation states in its catalytic activity.149... 

W.A. Corpe, Metal-binding properties of surface materials from marine bacteria, Dev. Ind. Microbiol. 16 (1975) 249-255. 

Like pesticides, heavy metals are traditionally tested by enzyme inhibition or modulation of catalytic activity. Several metalloproteins behave as chelators for specific metals with no known catalytic reactions. Such heavy metal binding sites exist in metallothioneins and in various protein elements of bacterial heavy metal mechanisms and have been exploited for specific detection through affinity events. Nevertheless and as previously mentioned, bacterial resistance mechanisms can also be linked to catalytic pathways. For instance, c5rtochromes c3 and hydrogenases from sulfate and sulfur reducing bacteria [284,285] are well suited for bioremediation purposes because they can reduce various metals such as U(V) and Cr(VI) [286,287]. Cytochrome c3 has been reported to catalyse Cr(VI) and U(VI) reduction in Desulfovibrio vulgaris [288,289], suggesting... 

Th + or AP" " induced a precipitate to form in all Bradyrhizobium and Sinorhi-zobium cultures tested, which suggested a defense mechanism based on metal precipitation by extracellular polymers (Santamaria et al., 2003). Among the metals tested, only Fe " ", Ap+, and Th were able to induce the formation of precipitate. AP+ is probably the natural soil component against which this defence mechanism could be directed, and a different defence mechanism based on extracellular aluminium precipitation within a gelatinous residue has been described for P. fluorescens (Appanna and St. Pierre, 1996). However, tliis polymer was composed mainly of phosphatidylethanolamine. While metal binding to extracellular polymers and bacterial surfaces have been proposed as the reason for increased metal resistance of biofilm-growing bacteria, this proposed defense mechanism involved the physical removal of the capsule after metal binding (Santamaria et al., 2003). 

Enterobactin is a cyclic triester of 2,3-dihydroxy-N-benzoyl-L-serine (Fig. 6). It is accumulated by E. coli and other bacteria when grown under low iron conditions and mediates the anabolic utilization of iron by these microbes, as do the hydroxamate siderochromes mentioned above (13, 21). In enterobactin, however, the metal-binding ligands are provided by catechol groups and the sustaining backbone is held together by ester, rather than by amide, bonds. 

Related Compounds sumably some antibiotics are delicately balanced so as to be able to compete successfully with the metal-binding agents of the bacteria while not disturbing the metal processing by the host. There is evidence that at least some bacteria have developed resistance to antibiotics through the development of altered enzyme systems that can compete successfully with the antibiotic.133 The action of the antibiotic need not be a simple competitive one. The chelating properties of the antibiotic may be used in metal transport across membranes or to attach the antibiotic to a specific site from which it can interfere with the growth of bacteria. 

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