Metal resistance in bacteria

Abstract

Bacteria have been examined that have developed very efficient and different mechanisms for tolerating heavy metals. Often normal toxic levels of metals have no effect on cell growth of resistant strains. In many organisms, the genes controlling metal resistance are carried on plasmids, which provide the bacteria with a competitive advantage over other organisms when metals are present. Not all metal-resistant bacteria contain plasmids. For example, a Pseudomonas sp. (research at the Canada Centre for Inland Waters and the University of Guelph) resistant to 1000 #g/ml lead, also displays multiple antibiotic resistance. Vertical and horizontal agarose gel electrophoresis of cleared lysates revealed that plasmids were not present, even though the organism was tolerant to extremely high concentrations of lead.Plasmid-encoded resistance may provide organisms with efflux and bypass mechanisms, enzymes which catalyze the transformation of metals to volatile forms, or make the bacterial cell wall impermeable to the metal(s).A problem still remains in actually defining the concentrations that distinguish metal-resistant from metal-sensitive bacteria. Some researchers have proposed mathematical equations, and used statistical an.alysis to solve this problem. Nevertheless, standard concentrations have not been uni-versally proposed and/or accepted by the scientific community. This task is complicated by the various forms of metals used, the effect of media components, pH, and culture conditions, which have the capability of influencing the toxicity of the metal.Research on metal-bacteria interactions is in some ways still in its early stages of development. Nevertheless, significant advances in scientific knowledge have been achieved over the last 20 years. To fill the existing gaps in knowledge, research will need to be conducted on the extent of metal resistance in bacteria, the relationship between metal and antibiotic resistance, mechanisms specified by the plasmids, and the ecology, physiology, and genetics of gene transfer in the natural environment.Since some microorganisms are responsible for environmental metal transformations, they may also serve as bioassay indicator organisms in polluted and non-polluted environments. Moreover, there may be potential biotechnological applications for metal-resistant bacteria in the area of toxic metal control in waste-water treatment. INTRODUCTIONThe genetic basis for metal resistance in bacteria is an area of intensive research both in the en-0168-6445/85/$03.30

Response of Bacterioplankton Communities to Cadmium Exposure in Coastal Water Microcosms with High Temporal Variability

“…Actually, high diversity and evenness seemed to be common features in marine microbial communities of many chemically polluted environments (9), probably because pollution disturbance generated conditions for the proliferation of rare taxa with stress resistance. According to the widely reported metal resistance of bacteria (38)(39)(40), the acute response of the bacterial community to the higher Cd levels at the early stage might be due to the proliferation rate of resistant taxa being higher than the extinction rate of sensitive taxa. However, this trend disappeared later, indicating that the temporal succession overwhelms Cd-induced patterns in the alpha diversity of bacterial community.…”

Arousing sleeping genes: shifts in secondary metabolism of metal tolerant actinobacteria under conditions of heavy metal stress

“…This type of pedogenesis results in 1.2-2.0 mg nickel per gram soil dry weight in nickel-rich serpentine soils (Mengoni et al 2001). Here, we isolated the strain Tosca3, displaying the most pronounced resistance (for calculating concentration of resistance see Duxbury 1981;Trevors et al 1985), from the ultramafic soil sample of Tuscany. There are only very few studies on antimicrobial characteristics of isolates originating from this type of soil.…”

The role of microbial metal resistance and detoxification mechanisms in environmental bioassay research

“…Mercury resistance has been extensively investigated and reviewed by numerous researchers (Foster, 1983;Robinson & Tuovinen, 1984;Brown, 1985;Trevors et al, 1985). Mercuryresistant bacteria have also been isolated from numerous environments including sediment samples .…”

“…This problem is also complicated by the various forms of metals used, and the influence that complexing agents and environmental conditions have on the availability and form of the metals. For a review of this problem with examples of metal concentrations found in the literature, the reader is referred to a review by Trevors et al (1985).…”