Genome-Scale Data Call for a Taxonomic Rearrangement of Geodermatophilaceae

Geodermatophilaceae (order Geodermatophilales, class Actinobacteria) form a comparatively isolated family within the phylum Actinobacteria and harbor many strains adapted to extreme ecological niches and tolerant against reactive oxygen species. Clarifying the evolutionary history of Geodermatophilaceae was so far mainly hampered by the insufficient resolution of the main phylogenetic marker in use, the 16S rRNA gene. In conjunction with the taxonomic characterisation of a motile and aerobic strain, designated YIM M13156T and phylogenetically located within the family, we here carried out a phylogenetic analysis of the genome sequences now available for the type strains of Geodermatophilaceae and re-analyzed the previously assembled phenotypic data. The results indicated that the largest genus, Geodermatophilus, is not monophyletic, hence the arrangement of the genera of Geodermatophilaceae must be reconsidered. Taxonomic markers such as polar lipids and fatty-acids profile, cellular features and temperature ranges are indeed heterogeneous within Geodermatophilus. In contrast to previous studies, we also address which of these features can be interpreted as apomorphies of which taxon, according to the principles of phylogenetic systematics. We thus propose a novel genus, Klenkia, with the type species Klenkia marina sp. nov. and harboring four species formerly assigned to Geodermatophilus, G. brasiliensis, G. soli, G. taihuensis, and G. terrae. Emended descriptions of all species of Geodermatophilaceae are provided for which type-strain genome sequences are publicly available. Our study again demonstrates that the principles of phylogenetic systematics can and should guide the interpretation of both genomic and phenotypic data.

Geodermatophilus daqingensis sp. nov., isolated from petroleum-contaminated soil

A novel Gram-positive actinobacterium, designated WT-2-1^T, was isolated from a sample of petroleum-contaminated soil collected in Daqing, Heilongjiang province, China and characterised using a polyphasic taxonomic approach. The optimal growth for strain WT-2-1^T was found to be at 25-35 °C and at pH 6.0-9.0 and with 0-4% (w/v) NaCl, forming blackish green-coloured colonies. Chemotaxonomic and molecular characteristics of the isolate match those described for members of the genus Geodermatophilus. The peptidoglycan was found to contain meso-diaminopimelic acid; galactose, glucose and xylose were detected as diagnostic sugars. The main phospholipids were identified as diphosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and phosphatidylglycerol; MK-9(H₄) was the dominant menaquinone present. The major cellular fatty acids were identified as iso-C_16:0 and iso-C_15:0. 16S rRNA gene sequence analysis showed that strain WT-2-1^T is a member of the genus Geodermatophilus, with high sequence similarities to Geodermatophilus aquaeductus BMG801^T (98.4%), Geodermatophilus saharensis CF5/5^T (98.4%), Geodermatophilus bullaregiensis BMG841^T (98.3%) and Geodermatophilus normandii CF5/3^T (98.3%). Based on the phenotypic characteristics, phylogenetic data and DNA-DNA hybridization results, the isolate is concluded to represent a novel species of the genus Geodermatophilus, for which the name Geodermatophilus daqingensis sp. nov. is proposed. The type strain is WT-2-1^T (=CGMCC 4.7381^T = DSM 104001^T).

Geodermatophilus pulveris sp. nov., a gamma-radiation-resistant actinobacterium isolated from the Sahara desert

A black-pigmented, aerobic actinobacterium, tolerant to ionizing radiation, designated BMG 825T, was isolated from desert limestone dust in Tunisia. The strain grew within the temperature range 10-40 °C, at pH 5.5-11.0 and in the presence of 2 % NaCl. The DNA G+C content was 75.7 mol%, and its cell-wall peptidoglycan contained meso-diaminopimelic acid. Sugars of whole-cell hydrolysates were galactose, glucose, and trace amounts of ribose and mannose. The predominant menaquinone was MK-9(H4), and the major fatty acids were iso-C16 : 0 and C16 : 1ω7c. The polar lipid profile comprised phosphatidylcholine, phosphatidylinositol, diphosphatidylglycerol, phosphatidylethanolamine, hydroxyphosphatidylethanolamine and an unspecified glycolipid. 16S rRNA gene sequence analysis revealed that the strain fell into the genus Geodermatophilus, showing the highest similarity with Geodermatophilus poikilotrophus DSM 44209T (99.1 %). DNA-DNA hybridization results, phylogenetic distinctiveness and phenotypic properties supported the classification of this strain as a representative of a novel species of the genus Geodermatophilus, for which the name Geodermatophilus pulveris sp. nov. is proposed. The type strain is BMG 825T (=CECT 9003T=DSM 46839‏T).

Geodermatophilus sabuli sp. nov., a γ-radiation-resistant actinobacterium isolated from desert limestone

A novel γ-radiation-resistant and Gram-staining-positive actinobacterium designated BMG 8133T was isolated from a limestone collected in the Sahara desert of Tunisia. The strain produced dry, pale-pink colonies with an optimum growth at 35–40 °C and pH 6.5–8.0. Chemotaxonomic and molecular characteristics of the isolate matched those described for members of the genus Geodermatophilus. The peptidoglycan contained meso-diaminopimelic acid as diagnostic diamino acid. The main polar lipids were phosphatidylcholine, diphosphatidylglycerol, phosphatidylinositol, phosphatidylethanolamine and one unspecified glycolipid. MK-9(H4) was the dominant menaquinone. Galactose and glucose were detected as diagnostic sugars. The major cellular fatty acids were branched-chain saturated acids iso-C16 : 0 and iso-C15 : 0. The DNA G+C content of the novel strain was 74.5 %. The 16S rRNA gene sequence showed highest sequence identity with Geodermatophilus ruber (98.3 %). Based on phenotypic results and 16S rRNA gene sequence analysis, strain BMG 8133T is proposed to represent a novel species, Geodermatophilus sabuli sp. nov. The type strain is BMG 8133T ( = DSM 46844T = CECT 8820T).

Exploring Actinobacteria assemblages in coastal marine sediments under contrasted Human influences in the West Istria Sea, Croatia

The exploration of marine Actinobacteria has as major challenge to answer basic questions of microbial ecology that, in turn, will provide useful information to exploit Actinobacteria metabolisms in biotechnological processes. The ecological functions performed by Actinobacteria in marine sediments are still unclear and belongs to the most burning basic questions. The comparison of Actinobacteria communities inhabiting marine sediments that are under the influence of different contamination types will provide valuable information in the adaptation capacities of Actinobacteria to colonize specific ecological niche. In the present study, the characterization of different Actinobacteria assemblages according to contamination type revealed the ecological importance of Actinobacteria for maintaining both general biogeochemical functions through a "core" Actinobacteria community and specific roles associated with the presence of contaminants. Indeed, the results allowed to distinguish Actinobacteria genera and species operational taxonomic units (OTUs) able to cope with the presence of either (i) As, (ii) metals Ni, Fe, V, Cr, and Mn, or (iii) polycyclic aromatic hydrocarbons (PAHs) and toxic metals (Hg, Cd, Cu, Pb, and Zn). Such observations highlighted the metabolic capacities of Actinobacteria and their potential that should be taken into consideration and advantage during the implementation of bioremediation processes in marine ecosystems.