Isolation and Characterization of Thallium-tolerant Bacteria from Heavy Metal-polluted River Sediment and Non-polluted Soils

Abstract

Thallium (Tl) is a heavy metal found in trace amounts in the earth's crust and has been studied to a much lesser degree than other heavy metals. Since the discovery of high-temperature superconducting components in the Tl-Ca-Ba-Cu-O system, Tl has attracted greater attention as a potential major pollution source of the future. In this study, the response of soil culturable bacterial communities to the addition of Tl was examined with fresh samples of non-polluted garden and arable soils. A preserved air-dried sample from heavy metal-polluted river sediment was also used as a reference. Soil suspension experiments were performed to homogenize the soils to evenly distribute both the microbial populations and Tl and reduce spatial variability. From soil suspensions loaded with Tl at 0.24 to 0.98 mM, bacteria tolerant to 0.49 mM Tl (100 mg Tl l −1 ) were isolated and characterized phylogenetically. The background level of culturable Tl-tolerant bacterial populations was 0.0003-0.013% for the non-polluted soils. The Tl-tolerant fraction increased rapidly in response to Tl loading and dominated the bacterial community, which might be attributed mainly to an immediate effect due to the death of Tl-sensitive microorganisms and leaking of nutrients from cell lysis of sensitive species supporting the growth of primarily Tl-tolerant heterotrophs. Such Tl-tolerant culturable bacteria were isolated and classified into 9 groups of Alphaproteobacteria, those from the arable soil were identified as Pseudomonas spp., and those from the contaminated river sediment were identified as Bacillus niacini.

Alsobacter metallidurans gen. nov., sp. nov., a thallium-tolerant soil bacterium in the order Rhizobiales

“…The almost-complete 16S rRNA gene sequence of strain SK200a-9 T (1448 bp) had been determined in our previous study (Bao et al, 2006). Sequence comparisons with representative bacteria differentiated this bacterium from all currently described members of the families…”

“…In general, pollution with Tl is restricted to specific areas such as in the vicinity of non-ferrous metal mines, smelters and factories using Tl (Wierzbicka et al, 2004;Peter & Viraraghavan, 2005;Yang et al, 2005;Xiao et al, 2012). In our previous study (Bao et al, 2006), soil bacteria tolerant to 0.49 mM Tl (100 mg Tl l 21 ) had been isolated from a non-polluted garden soil in Japan through a selective cultivation procedure. Phylogenetic analysis revealed that all of the 59 Tl-tolerant strains belonged to the class Alphaproteobacteria and that 17 of these strains constituted a distinct cluster (Group A; Bao et al, 2006) in the order Rhizobiales.…”

“…In our previous study (Bao et al, 2006), soil bacteria tolerant to 0.49 mM Tl (100 mg Tl l 21 ) had been isolated from a non-polluted garden soil in Japan through a selective cultivation procedure. Phylogenetic analysis revealed that all of the 59 Tl-tolerant strains belonged to the class Alphaproteobacteria and that 17 of these strains constituted a distinct cluster (Group A; Bao et al, 2006) in the order Rhizobiales. One member of this group, strain SK200a-9 T , had an MIC of 4.4 mM against Tl.…”

“…One member of this group, strain SK200a-9 T , had an MIC of 4.4 mM against Tl. Strain SK200a-9 T was also tolerant to other heavy metals such as cadmium (MIC, 0.4 mM), cobalt (1.7 mM), copper (0.8 mM), nickel (1.7 mM), lead (1.4 mM) and zinc (3.1 mM) (Bao et al, 2006). In this paper, we describe strain SK200a-9 T phenotypically, chemotaxonomically and phylogenetically and propose that it represents a novel species of a new genus.…”

Isolation of Octylphenol Polyethoxylate-Degrading Soil Bacteria: a Long-Term Soil Column Study

“…The dilution-plating method was used to enumerate culturable bacteria using 100-fold diluted nutrient broth (NB/ 100) as the culture medium 4,24) . Soil samples (5 g) were taken from the column before percolation (0 day) and at 129 and 300 days after exposure to OPEOn, suspended in 45 ml of sterile water, dispersed on an EYELA ultrasonic cleaner for 5 min, then diluted in a 10-fold stepwise manner with sterile water.…”