Effects of Streptomyces sp. HU2014 inoculation on wheat growth and rhizosphere microbial diversity under hexavalent chromium stress.

Wheat (Triticum aestivum L.) is a major foodstuff for over 40% of the world's population. However, hexavalent chromium [Cr(VI)] in contaminated soil significantly affects wheat production and its ecological environment. Streptomyces sp. HU2014 was first used to investigate the effects of Cr (VI) stress on wheat growth. We analyzed the Cr(VI) concentration, physicochemical properties of wheat and soil, total Cr content, and microbial community structures during their interactions. HU2014 reduced the toxicity of Cr(VI) and promoted wheat growth by increasing total nitrogen, nitrate nitrogen, total phosphorus, and Olsen-phosphorus in Cr(VI)-contaminated soil. These four soil variables had strong positive effects on two bacterial taxa, Proteobacteria and Bacteroidota, in the HU2014 treatments. In addition, the level of the dominant Proteobacteria positively correlated with the total Cr content in the soil. Among the fungal communities, which had weaker correlations with soil variables compared with bacterial communities, Ascomycota was the most abundant. Our findings suggest that HU2014 can promote the phytoremediation of Cr(VI)-contaminated soil.

Identification of a Novel Streptomyces sp. Strain HU2014 Showing Growth Promotion and Biocontrol Effect Against Rhizoctonia spp. in Wheat.

Wheat sharp eyespot is a serious disease caused by the phytopathogens Rhizoctonia cerealis and R. solani. Some species in the genus Streptomyces have been identified as potential biocontrol agents against phytopathogens. In this investigation, the physiological, biochemical, phylogenetic, and genomic characteristics of strain HU2014 indicate that it is a novel Streptomyces sp. most closely related to Streptomyces albireticuli. Strain HU2014 exhibited strong antifungal activity against R. cerealis G11 and R. solani YL-3. Ultraperformance liquid chromatography-mass spectrometry on the four extracts from the extracellular filtrate of strain HU2014 identified 10 chemical constituents in the Natural Products Atlas with high match levels (more than 90%). In an antifungal efficiency test on wheat sharp eyespot, two extracts significantly reduced the lesion areas on bean leaves infected by R. solani YL-3. The drenching of wheat in pots with spore suspension of strain HU2014 demonstrated a control efficiency of 65.1% against R. cerealis G11 (compared with 66.9% when treated by a 30% hymexazol aqueous solution). Additionally, in vitro and pot experiments demonstrated that strain HU2014 can produce indoleacetic acid, siderophores, extracellular enzymes, and solubilized phosphate, and it can promote plant growth. We conclude that strain HU2014 could be a valuable microbial resource for growth promotion of wheat and biological control of wheat sharp eyespot.