Cytochrome c Peroxidase (CcP) is a Molecular Determinant of the Oxidative Stress Response in the Extreme Acidophilic Leptospirillum sp. CF-1

Abstract

Bioleaching processes are used to recover metals from sulfidic ores. Biofilm formation on ores is important for bioleaching because the attached microorganisms start the leaching process by concentrating ferric ions in the extracellular matrix. It has been shown that hydrogen peroxide is spontaneously generated on the surface of ores and that it negatively influences the growth and activity of microorganisms. However, the mechanism by which bioleaching microorganisms tolerate exogenous H2O2 as an adaptive trait remains elusive. Herein, we demonstrate that the gene yhjA, encoding a predicted periplasmic cytochrome c peroxidase (CcP), is important for the response to exogenously generated oxidative stress in the iron-oxidizing acidophilic bacterium Leptospirillum sp. CF-1. Our results show that yhjA is co-transcribed with the genes encoding the peroxide-responsive transcription regulator PerR and peroxiredoxin AhpC. CcP activity, but not yhjA mRNA level, significantly increased in response to hydrogen peroxide and ferric ion exposure, suggesting a post-translational regulation. In agreement with these results, challenging planktonic cells with hydrogen peroxide significantly increased their attachment to pyrite surfaces. In summation, our results suggest that CcP is important to cope with exogenous H2O2, thus favoring the early steps of attachment to mineral substrates.

Deciphering the Role of Multiple Thioredoxin Fold Proteins of Leptospirillum sp. in Oxidative Stress Tolerance

“…ROS overproduction and oxidative stress induction by exposure to ferric iron in Leptospirillum sp. had been assessed previously [18,19]. Diamide was used because of its ability to induce generalized disulfide stress.…”

“…Cells were exposed for one hour to oxidative stress conditions with 260 mM ferric iron or 4 mM diamide. Changes in mRNA levels were estimated by real-time PCR and normalized against the 16S rRNA (rrsB) [19].…”

“…Leptospirillum strain CF-1 cultures were grown aerobically at 37 • C and 180 rpm as described previously [19]. Bacterial growth was measured by direct microscopic counting using the improved Neubaüer chamber.…”

“…The reactions were performed in the StepOne Real-Time PCR system (Applied Biosystems, Foster, CA, USA). The relative abundance of the transcripts of the genes was determined using the constitutively expressed rrsB gene (16S rDNA) [19]. The experiments were carried out in triplicate.…”

“…is an autotrophic obligate acidophilic bacterium that catalyzes dissimilatory Fe(II) oxidation. It serves as a model bacterium to elucidate the mechanisms used by acidophilic microorganisms to thrive under highly oxidative conditions [16][17][18][19]. Thirteen tfp genes (formerly trx) coding for predicted TFPs have been identified in Leptospirillum spp.…”