Streptomyces cameroonensis sp. nov., a Geldanamycin Producer That Promotes Theobroma cacao Growth.

The taxonomy of an actinobacterial strain, designated JJY4 ^T , was established using a polyphasic approach. JJY4 ^T was isolated from the rhizosphere of Chromolaena odorata in Yaoundé (Cameroon) during a project for the selection of biological control agents. Strain JJY4 ^T exhibited antimicrobial activities against bacteria, fungi, and oomycetes. Strain JJY4 ^T also exhibited the traits of plant growth-promoting rhizobacteria such as the solubilization of inorganic phosphate, production of siderophores and indole-3-acetic acid, and 1-aminocyclopropane-1-carboxylate deaminase activity. In planta assays performed on cocoa plantlets confirmed that strain JJY4 ^T exhibited strong abilities to promote plant growth and protect against Phytophthora megakarya, the main causal agent of cocoa pod rot. The formation of rugose-ornamented spores in spiral spore chains by strain JJY4 ^T is a typical feature of members found in the Streptomyces violaceusniger clade and, similar to some members of the clade, strain JJY4 ^T produces geldanamycin. A phylogenetic analysis based on 16S rRNA gene sequences confirmed this classification and suggests that strain JJY4 ^T be added to the subclade constituted of the type strains Streptomyces malaysiensis DSM 41697 ^T and Streptomyces samsunensis DSM 42010 ^T . However, DNA-DNA relatedness and physiological characteristics allowed for the differentiation of strain JJY4 ^T from its closest phylogenetic relatives. Based on these results, strain JJY4 ^T (=NRRL B-65369, =NBRC 112705) appears to represent a novel species in the S. violaceusniger clade for which the proposed name is Streptomyces cameroonensis sp. nov.