Abstract
The acid mine drainage (AMD) in Carnoulès (France) is characterized by the presence of toxic metals such as arsenic. Several bacterial strains belonging to the Thiomonas genus, which were isolated from this AMD, are able to withstand these conditions. Their genomes carry several genomic islands (GEIs), which are known to be potentially advantageous in some particular ecological niches. This study focused on the role of the “urea island” present in the Thiomonas CB2 strain, which carry the genes involved in urea degradation processes. First, genomic comparisons showed that the genome of Thiomonas sp. CB2, which is able to degrade urea, contains a urea genomic island which is incomplete in the genome of other strains showing no urease activity. The urease activity of Thiomonas sp. CB2 enabled this bacterium to maintain a neutral pH in cell cultures in vitro and prevented the occurrence of cell death during the growth of the bacterium in a chemically defined medium. In AMD water supplemented with urea, the degradation of urea promotes iron, aluminum and arsenic precipitation. Our data show that ureC was expressed in situ, which suggests that the ability to degrade urea may be expressed in some Thiomonas strains in AMD, and that this urease activity may contribute to their survival in contaminated environments.
Highlights
Acid mine drainage (AMD) environments are highly toxic to most living organisms due to the acidic conditions and the presence of elements such as arsenic, a stable microbial community composed of bacteria, archaea, and protists has been known for several years to inhabit the acid mine drainage (AMD)-impacted Reigous creek near Carnoulès (France; Bruneel et al, 2003, 2006, 2011; Duquesne et al, 2003, 2008; Bryan et al, 2009; Halter et al, 2011; Slyemi et al, 2011; Volant et al, 2012)
CB2, CB1, CB3, CB6, and Thiomonas arsenitoxydans 3As were isolated from AMD-impacted water collected at the Reigous creek in Carnoulès (France; Duquesne et al, 2008; Arsène-Ploetze et al, 2010), and Thiomonas intermedia K12 was isolated from a corroded concrete wall in the Hamburg sewer system (Milde et al, 1983)
One genomic islands (GEIs) 88.2 Kb in size (95 CDS) detected using this comparative genomic approach, which is present in the vicinity of another GEI (RGP10; Freel et al, in press) involved in arsenic resistance, was found to have the following characteristics: it is flanked by a miscRNA gene, contains several transposases and shows a compositional bias indicating possible acquisition by HGT
Summary
Acid mine drainage (AMD) environments are highly toxic to most living organisms due to the acidic conditions and the presence of elements such as arsenic, a stable microbial community composed of bacteria, archaea, and protists has been known for several years to inhabit the AMD-impacted Reigous creek near Carnoulès (France; Bruneel et al, 2003, 2006, 2011; Duquesne et al, 2003, 2008; Bryan et al, 2009; Halter et al, 2011; Slyemi et al, 2011; Volant et al, 2012). Chemical and microscopic tests were first conducted under laboratory conditions in order to determine whether these Thiomonas strains are able to degrade urea and if so, whether their urease activity may contribute to acid tolerance and survival.
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