Salt Stress-Induced Loss of Iron Oxidoreduction Activities and Reacquisition of That Phenotype Depend on rus Operon Transcription in Acidithiobacillus ferridurans
The type strain of the mineral-oxidizing acidophilic bacterium was grown in liquid medium containing elevated concentrations of sodium chloride with hydrogen as electron donor. While it became more tolerant to chloride, after about 1 year, the salt-stressed acidophile was found to have lost its abil...
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Veröffentlicht in: | Applied and environmental microbiology 2018-04, Vol.84 (7), p.e02795-17 |
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Zusammenfassung: | The type strain of the mineral-oxidizing acidophilic bacterium
was grown in liquid medium containing elevated concentrations of sodium chloride with hydrogen as electron donor. While it became more tolerant to chloride, after about 1 year, the salt-stressed acidophile was found to have lost its ability to oxidize iron, though not sulfur or hydrogen. Detailed molecular examination revealed that this was due to an insertion sequence, IS
, which belongs to the IS
subgroup of the IS
family, having been inserted downstream of the two promoters PI and PII of the
operon (which codes for the iron oxidation pathway in this acidophile), thereby preventing its transcription. The ability to oxidize iron was regained on protracted incubation of the culture inoculated onto salt-free solid medium containing ferrous iron and incubated under hydrogen. Two revertant strains were obtained. In one, the insertion sequence IS
had been excised, leaving an 11-bp signature, while in the other an ∼2,500-bp insertion sequence (belonging to the IS
family) was detected in the downstream inverted repeat of IS
The transcriptional start site of the
operon in the second revertant strain was downstream of the two ISs, due to the creation of a new "hybrid" promoter. The loss and subsequent regaining of the ability of
to reduce ferric iron were concurrent with those observed for ferrous iron oxidation, suggesting that these two traits are closely linked in this acidophile.
Iron-oxidizing acidophilic bacteria have primary roles in the oxidative dissolution of sulfide minerals, a process that underpins commercial mineral-processing biotechnologies ("biomining"). Most of these prokaryotes have relatively low tolerance to chloride, which limits their activities when only saline or brackish waters are available. The study showed that it was possible to adapt a typical iron-oxidizing acidophile to grow in the presence of salt concentrations similar to those in seawater, but in so doing they lost their ability to oxidize iron, though not sulfur or hydrogen. The bacterium regained its capacity for oxidizing iron when the salt stress was removed but simultaneously reverted to tolerating lower concentrations of salt. These results suggest that the bacteria that have the main roles in biomining operations could survive but become ineffective in cases where saline or brackish waters are used for irrigation. |
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ISSN: | 0099-2240 1098-5336 |
DOI: | 10.1128/AEM.02795-17 |