Survey of metal tolerance in moderately halophilic eubacteria

Abstract

The tolerance patterns, expressed as MICs, for 250 moderately halophilic eubacteria to 10 heavy metals were surveyed by using an agar dilution method. The moderate halophiles tested included 12 culture collection strains and fresh isolates representative of Deleya halophila (37 strains), Acinetobacter sp. (24 strains), Flavobacterium sp. (28 strains), and 149 moderately halophilic gram-positive cocci included in the genera Marinococcus, Sporosarcina, Micrococcus, and Staphylococcus. On the basis of the MICs, the collection strains showed, overall, similar responses to silver, cobalt, mercury, nickel, lead, and zinc. All were sensitive to silver, mercury, and zinc and tolerant of lead. The response to arsenate, cadmium, chromium, and copper was very heterogeneous. The metal susceptibility levels of the 238 freshly isolated strains were, in general, very heterogeneous among the four taxonomic groups as well as within the strains included in each group. The highest toxicities were found with mercury, silver, and zinc, while arsenate showed the lowest activity. All these strains were tolerant of nickel, lead, and chromium and sensitive to silver and mercury. Acinetobacter sp. strains were the most heavy-metal tolerant, with the majority of them showing tolerance of eight different metal ions. In contrast, Flavobacterium sp. strains were the most metal sensitive. The influence of salinity and yeast extract concentrations of the culture medium on the toxicity of the heavy metals tested for some representative strains was also studied. Lowering the salinity, in general, led to enhanced sensitivity to cadmium and, in some cases, to cobalt and copper. However, increasing the salinity resulted in only a slight decrease in the cadmium, copper, and nickel toxicities. Reduction in the yeast extract concentration resulted in an increased sensitivity to all metals, especially when this component was lowered to 0.01% (wt/vol). In contrast, a higher concentration only slightly lessened the toxicities of nickel and zinc.

Microbial community structure and activity in arsenic-, chromium- and copper-contaminated soils

“…are able to grow at high bioavailable concentrations of As. Nieto et al [44] and Deshpande et al [45] have similarly found that Acinetobacter strains were highly resistant to various metals and that several Acinetobacter spp. were commonly found at metal-contaminated sites.…”

Copper-resistant halophilic bacterium isolated from the polluted Maruit Lake, Egypt

“…The agar dilution method was used to determine the bacterial resistance to toxic metals (Washington and Sutter 1980). Various concentrations of heavy metals (0AE05, 0AE01, 0AE1, 0AE5, 1AE0, 1AE5, 2AE0, 2AE5, 5AE0, 7AE0, 9AE0, 10AE0, 20AE0 and 40AE0 mmol l )1 ) were examined as in a previous study on metal tolerance of moderately halophilic eubacteria (Nieto et al 1989). The appropriate concentrations of heavy metals were added to 100-ml Erlenmeyer flasks containing 20-ml nutrient agar medium and 1AE0 mol l )1 NaCl as the optimal concentration for strain MA2 growth.…”

“…Very few studies on the interactions of moderate halophiles with toxic metals have been reported (Onishi et al 1984). Such information is desirable because some of these metal-resistant halophilic bacteria could be used as bioassay indicators in saline aquatic polluted environments (Nieto et al 1989). Recently, copper uptake was investigated in halophilic bacteria isolated from the Dead Sea shore in Jordan: copper ions were found to accumulate in the cell wall or between the cell wall and the plasma membrane (Fouad et al 2007).…”

Role of a serine-type d-alanyl-d-alanine carboxypeptidase on the survival ofOchrobactrumsp. 11a under ionic and hyperosmotic stress

“…The toxicity to heavy metals such as Al, Cu, and Zn was assayed on AN medium because it had been shown previously that metal toxicity can be heavily influenced by environmental factors such as pH, clay minerals, and inorganic anionic and cationic components (Babich & Stotzky, 1980). In general, media containing salts, such as minimal media, lead to a decreased sensitivity to heavy metals (Nieto et al, 1989). Our results showed that the PBP mutant displayed an enhanced sensitivity to KCl and LiCl, compared with the wild-type strain, because its growth was severely reduced and completely inhibited by these salts at 300 and 400 mM, respectively (Table 2).…”