Geodermatophilus poikilotrophi sp. nov.: a multitolerant actinomycete isolated from dolomitic marble

Abstract

A novel Gram-reaction-positive, aerobic actinobacterium, tolerant to mitomycin C, heavy metals, metalloids, hydrogen peroxide, desiccation, and ionizing- and UV-radiation, designated G18T, was isolated from dolomitic marble collected from outcrops in Samara (Namibia). The growth range was 15-35°C, at pH 5.5-9.5 and in presence of 1% NaCl, forming greenish-black coloured colonies on GYM Streptomyces agar. Chemotaxonomic and molecular characteristics of the isolate matched those described for other representatives of the genus Geodermatophilus. The peptidoglycan contained meso-diaminopimelic acid as diagnostic diaminoacid. The main phospholipids were phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, and small amount of diphosphatidylglycerol. MK-9(H4) was the dominant menaquinone and galactose was detected as diagnostic sugar. The major cellular fatty acids were branched-chain saturated acids iso-C16:0 and iso-C15:0 and the unsaturated C17:1 ω8c and C16:1 ω7c. The 16S rRNA gene showed 97.4-99.1% sequence identity with the other representatives of genus Geodermatophilus. Based on phenotypic results and 16S rRNA gene sequence analysis, strain G18T is proposed to represent a novel species, Geodermatophilus poikilotrophi. Type strain is G18T (=DSM 44209T=CCUG 63018T). The INSDC accession number is HF970583. The novel R software package lethal was used to compute the lethal doses with confidence intervals resulting from tolerance experiments.

Figure 1

Scanning electron micrograph of strain G18^T grown on GYM Streptomyces medium for 7 days at 28°C.

Figure 2

Maximum likelihood phylogenetic tree inferred from 16S rRNA gene sequences, showing the phylogenetic position of strain G18^T relative to the type strains within the family cursive. The branches are scaled in terms of the expected number of substitutions per site (see size bar). Support values from maximum-likelihood (left) and maximum-parsimony (right) bootstrapping are shown above the branches if equal to or larger than 60%.

Figure 3

Estimation of survival following exposure to gamma-radiation (a), UV-radiation (b), mitomycin C (c), hydrogen peroxide (d), and desiccation (e) for strain G18^T and G. obscurus DSM 43160^T as positive control. The mean c.f.u.mL⁻¹ per strain is given together with the LD50 and LD10 values in the upper panel of each figure; y-axis is on a logarithmic scale ((a)–(c), (e)), or on a square root scale (d). The lower panel depicts LD10 and LD50 values per strain and the differences between strains together with confidence intervals. Confidence intervals that do not contain zero (dashed vertical line) indicate significant differences to zero; in case of strain differences this indicates significant differences between strains.