Bacteria arsenic-resistant

Mielke, R.E., Southam, G. and Nordstrom, D.K. (2000) Arsenic resistant/oxidizing bacteria in acidic geothermal environments, Yellowstone National Park, Wyoming. Abstracts with Programs. The Geological Society of America, 32(7), 190. 

Inorganic arsenic oxyanions, frequently present as environmental pollutants, are very toxic for most micro-organisms. Many microbial strains possess genetic determinants that confer resistance. In bacteria, these determinants are often found on plasmids, which has facilitated their smdy to the molecular level. Bacterial plasmids conferring arsenic resistance encode speciflc efflux pumps able to extrude arsenic from the cell cytoplasm, thus lowering the intracellular concentration of the toxic ions. Recently, apparently similar arsenic membrane transport proteins have been found with yeast, plants, and animals (8,9) (see Sec. V, below). 

Arsenic resistance is not the only toxic heavy metal ion resistance system found in bacteria. Bacteria have known plasmid and chromosomal genes for resistances to Ag+, As02, ASO4 -, Cd ", Co ", CrO/-, Cu ", Hg +, Ni +, Pb ", Sb ",... 

In addition to the widespread (almost universal) chromosomal and plasmid arsenic resistance determinants, a few bacteria confer resistance to arsenite alone with a separate determinant for enzymatic oxidation of more-toxic arsenite to... 

Bacterial resistance to arsenic ions governed by plasmids was first discovered by Novick and Roth (17) in a group of Staphylococcus aureus p-lactamase plasmids that determine resistances to antibiotics and also to heavy metals. Arsenic resistance plasmids confer tolerance to both arsenate and arsenite as well as to antimony (III) (18). Resistance to all three ions is inducible and cross-induction among them occurs (18). Arsenic resistance determinants are very common in plasmids of both gram-negative and gram-positive bacteria. 

Arsenate reductases, initially characterized from plasmid R773 of gramnegative bacteria and plasmid pI258 of gram-positive S. aureus both reduce arsenate to arsenite and both confer arsenate resistance (21,34,36). However, their in vitro measured properties are very different and their energy coupling is different. As the amino acid sequences are only 15% identical, it appears that arsenate reductase enzymatic activity evolved twice independently among bacterial types... 

In addition to plasmid arsenic resistance that is well understood and for which clusters of genes have been isolated and sequenced, there are bacterial arsenic metabolism systems that involve oxidation of arsenite to arsenic. Arsenite oxidation by aerobic pseudomonads was first found with bacteria isolated from cattle dipping solutions where arsenicals were used as agents against ticks around the time of World War I. They were subsequently isolated by Turner and Legge... 

Arsenate resistance in some bacteria occurs via an ars operon that encodes proteins involved in arsenate reduction to arsenite, and ATP-dependent efflux of arsenite (25-29). The presence of this system has not been demonsttated in arsenite-oxidizing bacteria. 

This is enough evidence to provide the verdict that the Mono Lake bacteria are not arsenate utilizing but are merely arsenate resistant. This showed that they are not... 

Chang, J.S., Kim, YH. Kim, K.W. (2008) The ars genotype characterization of arsenic-resistant bacteria from arsenic-contaminated gold-silver mines in the Republic of Korea. Applied Microbiology and Biotechnology, 80, 155-165. 

Some bacteria are resistant to penicillin, because they produce an enzyme, penicillinase, that destroys the /3-lactam ring in the antibiotic. Synthesis of analogs afforded a partial solution to this problem. Ultimately, however, it became necessary to turn to antibiotics with completely different modes of action. Erythromycin, produced by a strain of Streptomyces bacteria first found in soil samples in the Philippines in 1952, functions in a distinct manner. It is a large ring lactone that interferes with the bacterial ribosome, its cell-wall protein S5mthesis factory. Although erythromycin is unaffected by penicillinase, bacteria resistant to it have developed over the decades since its introduction into the antibiotic arsenal. 

Maeda, S., Ohki, A., Miyaha K., Higashi, S., and Naka, K.(1992). Biomethylation of methylated arsenic compounds by arsenic-resistant bacteria Klebsiella oxytoca and Xanthomonas sp.). Appl Organomet. Chem., 6,415-420. 

These mechanisms are of considerable microbiological and biochemical interest, although not all of the above agents find current use as biocides. The plasmid-mediated efflux pumps are particularly important, since efflux is one means whereby acquired resistance to antibiotics occurs (see earlier) and can be a mechanism of resistance to some clinically useful biocides (see later). No efflux pump comparable to those described for arsenate and cadmium [212] has yet been detected in silver-resistant bacteria [213] however, an up-to-date assessment of this subject is available [212]. 

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