Identification and molecular genetic analysis of multiple loci contributing to high-level tellurite resistance in Rhodobacter sphaeroides 2.4.1

Abstract

The ability of the facultative photoheterotroph Rhodobacter sphaeroides to tolerate and reduce high levels of tellurite in addition to at least 10 other rare earth metal oxides and oxyanions has considerable potential for detoxification and bioremediation of contaminated environments. We report the identification and characterization of two loci involved in high-level tellurite resistance. The first locus contains four genes, two of which, trgAB, confer increased tellurite resistance when introduced into the related bacterium Paracoccus denitrificans. The trgAB-derived products display no significant homology to known proteins, but both are likely to be membrane-associated proteins. Immediately downstream of trgB, the cysK (cysteine synthase) and orf323 genes were identified. Disruption of the cysK gene resulted in decreased tellurite resistance in R. sphaeroides, confirming earlier observations on the importance of cysteine metabolism for high-level tellurite resistance. The second locus identified is represented by the telA gene, which is separated from trgAB by 115 kb. The telA gene product is 65% similar to the product of the klaB (telA) gene from the tellurite-resistance-encoding kilA operon from plasmid RK2. The genes immediately linked to the R. sphaeroides telA gene have no similarity to other components of the kilA operon. R. sphaeroides telA could not functionally substitute for the plasmid RK2 telA gene, indicating substantial functional divergence between the two gene products. However, inactivation of R. sphaeroides telA resulted in a significant decrease in tellurite resistance compared to the wild-type strain. Both cysK and telA null mutations readily gave rise to suppressors, suggesting that the phenomenon of high-level tellurite resistance in R. sphaeroides is complex and other, as yet uncharacterized, loci may be involved.

Identification and characterization of in vivo attenuated mutants of Brucella melitensis

“…This may explain the attenuation of this category of mutants. However, the role of CysK in tellurite and oxyanion resistance in Rhodobacter (O'Gara et al, 1997) suggests that the cys regulon may also be involved in protection against reactive oxygen intermediates. This is supported by our finding that the cysI mutant (C4) is more sensitive to H 2 O 2 than the parental strain.…”

The hyperthermophilic anaerobe Thermotoga Maritima is able to cope with limited amount of oxygen: insights into its defence strategies

“…It has been recently shown in E. coli, that this protein is highly expressed in chromate stress (Ackerley et al, 2006). In the same way, disruption of this gene resulted in a decreased resistance of Gram-negative bacteria to potassium tellurite, a pro-oxidant heavy metal compound (O'Gara et al, 1997). An O-acetylhomoserine sulfhydrylase, which is also involved in cysteine biosynthesis (locus tag TM_0882), was also shown to be overproduced in oxidative conditions.…”

On the mechanism of resistance to channel-forming colicins (PacB) and tellurite, encoded by plasmid Mip233 (IncHI3)

“…Considering the chemical and physical similarities of tellurium and sulfur, we suggest that a pacB product may be involved in the reduction of tellurite salts to metallic tellurium, conferring protection against the toxic effects of tellurite. In support to this hypothesis, resistance to tellurite has been associated with two loci (one identi-¢ed as cysK) in Rhodobacter sphaeroides [20].…”