1-Aminocyclopropane-1-carboxylate (ACC) deaminase is a plant growth promoting (PGP) trait found in beneficial bacteria including streptomycetes and responsible for stress modulation. The ACC deaminase gene, acdS, of S. venezuelae ATCC 10712 was cloned into an expression plasmid, pIJ86, to generate S. venezuelae/pIJ86-acdS. Expression of acdS and production of ACC deaminase of S. venezuelae/pIJ86-acdS were significantly higher than the unmodified strain. The ACC deaminase-overexpressing mutant and the wild type control were inoculated into Thai jasmine rice (Oryza sativa L. cv. KDML105) under salt stress conditions. S. venezuelae on its own augmented rice growth and significantly increased more tolerance to salinity by reduction of ethylene, reactive oxygen species (ROS) and Na+ contents, while accumulating more proline, total chlorophyll, relative water content (RWC), malondialdehyde (MDA), and K+ than those of uninoculated controls. The overproducer did not alter chlorophyll, RWC, or MDA further–while it did boost more shoot weight and elongation, and significantly regulated salt tolerance of rice by increasing proline and reducing ethylene and Na+ contents further than that of the wild type. This work is the first illustration of the beneficial roles of S. venezuelae to enhance plant fitness endophytically by promotion of growth and salt tolerance of rice.

A novel endophytic actinomycete strain GKU 173T isolated from the roots of Acacia mangium Willd. showed potential plant growth promoting (PGP) activity. Phylogenetic analysis, based on 16S rRNA gene, indicated that strain GKU 173T was the most closely related to Fodinicola feengrottensis HKI 0501T—the only species in the genus Fodinicola. Morphology and chemotaxonomy of strain GKU 173T indicated that it belongs to the genus Fodinicola by having meso-diaminopimelic acid in the cell wall and xylose as the characteristic cell-wall sugars. The cellular fatty acid profile mainly comprised iso-C16:0, anteiso-C17:0, iso-C18:0, and iso-C17:0. The major menaquinones were MK-9(H4), MK-9(H6), and MK-9(H8). The main polar phospholipids contained diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Genome analysis signified DNA G+C content of 67.81 mol%. The level of digital DNA-DNA relatedness between strain GKU 173T and the type strain was 21.30%. On the basis of polyphasic characteristics, strain GKU 173T clearly represents a novel species of the genus Fodinicola, for which the name Fodinicola acaciae sp. nov. (= TBRC 10620T = NBRC 114213T) is proposed. Furthermore, genome analysis of both strains suggested that members of the genus Fodinicola are promising sources of beneficial PGP-actinomycetes and novel secondary metabolites.