Arthrobacter wenxiniae sp. nov., a novel plant growth-promoting rhizobacteria species harbouring a carotenoids biosynthetic gene cluster.

A bacterial strain, designated AETb3-4T was isolated from the rhizosphere of lily. Comparison of 16S rRNA gene sequences showed that the sequence from strain AETb3-4T exhibits high sequence similarity with those of Arthrobacter silviterrae KIS14-16T (97.9%), Arthrobacter livingstonensis LI2T (97.2%) and Arthrobacter stackebrandtii CCM 2783T (97.0%). Whole genome average nucleotide identity (ANI) and the digital DNA-DNA hybridization (dDDH) values between strain AETb3-4T and the reference strains A. silviterrae DSM 27180T, A. livingstonensis L12T and A. stackebrandtii DSM 16005T were below 83.6% and 27.7%, respectively, values which are considerably below the proposed thresholds for the species delineation, consistent with the proposal that strain AETb3-4T represents a novel species. The genome size of strain AETb3-4T is 4.33 Mb and the genomic DNA G + C content is 67.3%. The main polar lipids were identified as phosphatidylglycerol, diphosphatidylglycero, phosphatidylinositol and an unidentified glycolipid. The major fatty acids (> 10%) were identified as anteiso-C15: 0 and anteiso-C17: 0. The predominant menaquinone was found to be menaquinone 9 (MK-9) (H2) (82.2%). Phenotypic tests allowed the strain to be differentiated from its close phylogenetic neighbors. Based on the results obtained, it is proposed that the strain AETb3-4T (= CFCC 16390T = LMG 31708T) represents a novel species in the genus Arthrobacter, for which the names Arthrobacter wenxiniae sp. nov. is proposed. In addition, the novel strain AETb3-4T has multiple plant growth-promoting characters including ACC-deaminase activity and production of IAA. Furthermore, the genome contains secondary metabolite biosynthesis gene clusters, including a carotenoid biosynthetic gene cluster, suggesting potential capacities for secondary metabolite synthesis. These data suggest that strain AETb3-4T may have potential applications both in medicine and sustainable agriculture.

Optimization of submerged fermentation of Thelephora ganbajun zang.

The effects of the fermentation conditions on both the biomass yield and the organic selenium yield of Thelephora ganbajun zang were studied. The components most suitable for the submerged fermentation medium were examined using the orthogonal array method; they comprised sucrose at 30 g L(-1) , carbamide 1 g L(-1) , corn steep liquor 8 g L(-1) , MgSO4 ·7H2 O 0.3 g L(-1) , KH2 PO4 0.5 g L(-1) , and NaCl 5 g L(-1) . The optimum cultivation conditions that resulted in maximal biomass yield were obtained using the response surface methodology (RSM). The conditions were as follows: initial pH, 5.84; temperature, 26.16 °C; and rotation speed, 170 rpm. Feeding sucrose led to a higher biomass yield, with a maximum of 21.20 g L(-1) . The biomass yield and the organic Se yield of T. ganbajun could reach 10.8 g L(-1) and 3256.07 mg kg(-1) , respectively, in a culture medium supplemented with 200 mg L(-1) sodium selenite (Na2 SeO3 ), which was added to the medium at 36 h after inoculation. Application of the orthogonal array method and RSM gave rise to a significant enhancement in the biomass yield of T. ganbajun. The results of these experiments indicate that T. ganbajun is a promising microorganism for selenium enrichment.