1 g L-1 YE 0.2 g L-1 3As + 10 100 2.9 / + + + – + ++ +++ – - (69%) – (67%) Ynys1 – 5 12.5 5.6 – (35%) – + – - nd – +++ – nd nd WJ68 + 10 > 100 38.7 + (6%) + + – - nd ++ +++ – nd nd Tm. arsenivorans

+ 10 100 4.5 + (24%) + – + ++ ++ ++ +++ ++ + (25%) / Tm. perometabolis – 5 > 100 0 / – + – - nd – +++ – nd nd a Diameter (mm) of swimming ring formed on 0.3% agar plates after 72 h incubation expressed as a difference with non motile strains (forming colonies of < 3 mm diameter); bMotility was tested in the presence of 1.33 check details mM of arsenite: “”+”" indicates a diameter of swimming ring greater than in absence of arsenite, “”-”" a smaller one and “”/”" no change. cBasel medium (MCSM or m126) amended with either yeast extract (YE), thiosulfate or arsenite or combinations thereof. d5,33 mM in case of 3As, WJ68, and Tm. arsenivorans, 2.67 mM in case of Ynys1 and Tm. perometabolis. eGrowth is expressed as an increase of colony forming units (cfu) observed after 10 days; -, no increase; fTested with 0.1, 0.2, 0.3% or 0.5% YE in absence of As(III), with 0.1, 0.2 or 0.3% YE and 1.3 mM of As(III), or with 0.3% YE and 2.6 mM As(III), except for WJ68, tested in 0.5% YE, without As(III). g1.33 mM As(III) in MCSM. nd: no data. The MIC of As(III) for strains 3As, WJ68 and T. arsenivorans was 10 mM, higher than for strains

Ynys1 and T. perometabolis (Table 1). Additionally, strain Ynys1 was more sensitive to As(V) than the other strains. Arsenic PI3K Inhibitor Library screening resistance in bacteria is in part due to the expression of aox genes but

also of the ars arsenic-resistance genes [8]. Among these, arsC encodes an arsenate reductase and arsA and arsB encode an arsenite efflux pump. Analysis of the Thiomonas sp. 3As genome (Arsène-Ploetze & Bertin, unpublished) revealed the presence of two copies of the arsB gene, denoted arsB1 and arsB2. These genes were found to be distantly related, sharing just 70.2% sequence identity. In order to compare the occurrence, copy number and type of ars genes present in the different Tolmetin Thiomonas strains, PCR amplifications using generic arsB primers were performed. As expected, RFLP and sequence analysis confirmed the presence of the arsB1 and arsB2 genes in strain 3As (Table 1). In contrast, only the arsB1 gene could be detected using DNA from T. perometabolis, Ynys1 and WJ68, even when internal primers specific for the arsB2 gene were used. Conversely, only the arsB2 gene was detected in T. arsenivorans. The phylogeny of the arsB1 and arsB2 genes was analysed, excluding the sequences obtained using the arsB2 internal primers that were too short. The arsB2 gene sequence for strain 3As was taken directly from the annotated genome (Arsène-Ploetze & Bertin, unpublished). The data showed that while they are all related to the arsB genes of Leptospirillum spp.