Integrative analysis of microbiome and metabolome revealed the effect of microbial inoculant on microbial community diversity and function in rhizospheric soil under tobacco monoculture.

Over-application of chemical fertilizers and continuous cropping obstacles seriously restrict the sustainable development of tobacco production. Localized fertilization of beneficial microbes has potential advantages in achieving higher productivity, but the underlying biological mechanisms of interactions between rhizospheric microorganisms and the related metabolic cycle remain poorly characterized. Here, an integrative analysis of microbiomes with non-targeted metabolomics was performed on 30 soil samples of rhizosphere, root surrounding, and bulk soils from flue-cured tobacco under continuous and non-continuous monocropping systems. The analysis was conducted using UPLC-MS/MS platforms and high-throughput amplicon sequencing targeting the bacterial 16S rRNA gene and fungal ITS gene. The microbial inoculant consisted of Bacillus subtilis, B. velezensis, and B. licheniformis at the ratio of 1:1:1 in effective microbial counts, improved the cured leaf yield and disease resistance of tobacco, and enhanced nicotine and nitrogen contents of tobacco leaves. The bacterial taxa Rhizobium, Pseudomonas, Sphingomonadaceae, and Burkholderiaceae of the phylum Proteobacteria accumulated in high relative abundance and were identified as biomarkers following the application of the microbial inoculant. Under continuous monocropping, metabolomics demonstrated that the application of the microbial inoculant significantly affected the soil metabolite spectrum, and the differential metabolites were significantly enriched to the synthesis and degradation of nicotine (nicotinate and nicotinamide metabolism and biosynthesis of alkaloids derived from nicotinic acid). In addition, microbes were closely related to the accumulation of metabolites through correlation analysis. The interactions between plant roots and rhizospheric microorganisms provide valuable information for understanding how these beneficial microbes affect complex biological processes and the adaption capacity of plants to environments.IMPORTANCEThis study elaborated on how the microbial fertilizer significantly changed overall community structures and metabolite spectrum of rhizospheric microbes, which provide insights into the process of rhizosphere microbial remolding in response to continuous monocropping. we verified the hypothesis that the application of the microbial inoculant in continuous cropping would lead to the selection of distinct microbiota communities by establishing models to correlate biomarkers. Through correlation analysis of the microbiome and metabolome, we proved that rhizospheric microbes were closely related to the accumulation of metabolites, including the synthesis and degradation of nicotine. The interactions between plant roots and rhizospheric microorganisms provide valuable information for understanding how these beneficial microbes affect complex biological processes and the adaption capacity of plants to environments.

Gene cloning of a highly active phytase from Lactobacillus plantarum and further improving its catalytic activity and thermostability through protein engineering.

Phytase belongs to orthophosphate monoester hydrolase, which can catalyze the gradual hydrolysis of phytic acid to inositol phosphate. It can be added to animal feed to reduce the anti-nutritional factor of phytic acid in feed. The thermostability and specific activity of phytases are two key factors determining their potential applications. In this study, a highly active 233-aa phytase gene (LpPHY233) from Lactobacillus plantarum was cloned and expressed in Escherichia coli (E. coli), achieving 800 times higher activity than that expressed in L. plantarum. Next, the temperature characteristic and catalytic performance of LpPHY233 was improved by disulfide bond engineering and C-terminal truncation, respectively. Surprisingly, the specific activity of the C-terminal truncated mutant LpPHY200 was about 5.6 times higher than that of LpPHY233, and the optimal temperature for the mutant LpPHY233S58C/K61C introduced disulfide bond was 15 °C higher than that of LpPHY233. Moreover, these phytase mutants displayed excellent pH property and kinetic parameters, and have great application prospect in feed additives field. The molecular basis for its catalytic performance was preliminarily explained by in silico design methods. Our results provided a solid theoretical foundation for further molecular modification and industrial application of phytases.