A novel strain of Actinopolyspora mortivallis with antibacterial activity isolated from a Saharan soil

Abstract

A new halophilic actinomycete strain, designated H16, has been isolated from a hypersaline Saharan soil in Ouargla province (southern Algeria) and characterized taxonomically using a polyphasic approach. The strain grew at 18–50°C, pH 5–9, and 7–32% (w/v) NaCl. It produced abundant aerial mycelia, which formed long chains of rod-shaped spores at maturity, and fragmented substrate mycelia. The strain contained chemotaxonomic markers that were diagnostic for the genus Actinopolyspora, such as meso-diaminopimelic acid, arabinose, and galactose, phosphatidylcholine as a diagnostic phospholipid, and predominant menaquinones MK-9(H4) and MK-10(H4). The predominant fatty acids were anteiso- and iso-C17:0, iso-C15:0, and 9-methyl-C16:0. Phylogenetic analysis, based on 16S rDNA gene sequences, confirmed that strain H16 is a member of the genus Actinopolyspora and most closely related to A. mortivallis (98.7% identity). DNA–DNA hybridization confirmed that it belonged to A. mortivallis. This strain showed high activity against Klebsiella pneumoniae and optimally secreted antibiotics during the mid-stationary growth phase in liquid culture. The antibiotics were extracted with n-butanol and separated on silica gel plates by ethanol–ammonia–water (mobile phase). The results of bioautography revealed the presence of five antibiotics. The chemical revelations showed that these antibiotics were glycosylated polycyclic aromatic compounds containing amine groups and hydroxamic acids. The UV-visible and mass spectra of the most active antibiotics were determined.