Analysis and Functional Prediction of Core Bacteria in the Arabidopsis Rhizosphere Microbiome under Drought Stress.

The effects of global warming, population growth, and economic development are increasing the frequency of extreme weather events, such as drought. Among abiotic stresses, drought has the greatest impact on soil biological activity and crop yields. The rhizosphere microbiota, which represents a second gene pool for plants, may help alleviate the effects of drought on crops. In order to investigate the structure and diversity of the bacterial communities on drought stress, this study analyzed the differences in the bacterial communities by high-throughput sequencing and bioinformatical analyses in the rhizosphere of Arabidopsis thaliana under normal and drought conditions. Based on analysis of α and ß diversity, the results showed that drought stress had no significant effect on species diversity between groups, but affected species composition. Difference analysis of the treatments showed that the bacteria with positive responses to drought stress were Burkholderia-Caballeronia-Paraburkholderia (BCP) and Streptomyces. Drought stress reduced the complexity of the rhizosphere bacterial co-occurrence network. Streptomyces was at the core of the network in both the control and drought treatments, whereas the enrichment of BCP under drought conditions was likely due to a decrease in competitors. Functional prediction showed that the core bacteria metabolized a wide range of carbohydrates, such as pentose, glycans, and aromatic compounds. Our results provide a scientific and theoretical basis for the use of rhizosphere microbial communities to alleviate plant drought stress and the further exploration of rhizosphere microbial interactions under drought stress.

Isolation and Identification of Biocontrol Bacteria against Atractylodes Chinensis Root Rot and Their Effects.

Fusarium root rot (FRR) seriously affects the growth and productivity of A. chinensis. Therefore, protecting A. chinensis from FRR has become an important task, especially for increasing A. chinensis production. The purpose of this study was to screen FRR control strains from the A. chinensis rhizosphere soil. Eighty-four bacterial strains and seven fungal strains were isolated, and five strains were identified with high inhibitory effects against Fusarium oxysporum (FO): Trichoderma harzianum (MH), Bacillus amyloliquefaciens (CJ5, CJ7, and CJ8), and Bacillus subtilis (CJ9). All five strains had high antagonistic effects in vitro. Results showed that MH and CJ5, as biological control agents, had high control potential, with antagonistic rates of 86.01% and 82.78%, respectively. In the pot experiment, the growth levels of roots and stems of A. chinensis seedlings treated with MH+CJ were significantly higher than those of control plants. The total nitrogen, total phosphorus, total potassium, indoleacetic acid, and chlorophyll contents in A. chinensis leaves were also significantly increased. In the biocontrol test, the combined MH + CJ application significantly decreased the malondialdehyde content in A. chinensis roots and significantly increased the polyphenol oxidase, phenylalanine ammonolyase, and peroxidase ability, indicating a high biocontrol effect. In addition, the application of Bacillus spp. and T. harzianum increased the abundance and diversity of the soil fungal population, improved the soil microbial community structure, and significantly increased the abundance of beneficial strains, such as Holtermanniella and Metarhizium. The abundance of Fusarium, Volutella, and other pathogenic strains was significantly reduced, and the biocontrol potential of A. chinensis root rot was increased. Thus, Bacillus spp. and T. harzianum complex bacteria can be considered potential future biocontrol agents for FRR.

Addition of cellulose degrading bacterial agents promoting keystone fungal-mediated cellulose degradation during aerobic composting: Construction the complex co-degradation system.

To excavate a complex co-degradation system for decomposing cellulose more efficiently, cellulose-degrading bacteria, including Bacillus subtilis WF-8, Bacillus licheniformis WF-11, Bacillus Cereus WS-1 and Streptomyces Nogalater WF-10 were added during maize straw and cattle manure aerobic composting. Bacillus and Streptomyces successfully colonized, which improve cellulose degrading ability. Continuous colonization of cellulose-degrading bacteria can promote the fungi to produce more precursors for humus and promote the negative correlation with Ascomycota. In the current study, the addition of cellulose-degrading bacteria has resulted in the rapid development of Mycothermus and Remersonia in the phylum Ascomycota as keystone fungal genera which constitute the foundation of the co-degradation system. Network analysis reveals the complex co-degradation system of efficient cellulose bacteria and mature fungi to treat cellulose in the process of straw aerobic composting mainly related to the influence of total carbon (TC) /total nitrogen (TN) and humic acid (HA)/fulvic acid (FA). This research offers a complex co-degradation system more efficiently to decompose cellulose aiming to maintain the long-term sustainability of agriculture.

Culturable Screening of Plant Growth-Promoting and Biocontrol Bacteria in the Rhizosphere and Phyllosphere of Wild Rice.

Wild rice is an important improved resource for cultivated rice and its unique ability to resist biotic and abiotic stress has attracted the attention of many scholars. The microbial community structure in the rhizosphere and leaf area of different rice varieties is also different, which may be one of the reasons for the difference in stress resistance between wild rice and cultivated rice. Forty-six bacteria were screened from the rhizosphere and phyllospheric of four different wild rice varieties. The results of functions of the screened strains showed that 18 strains had a good inhibitory effect on rice blast, and 33 strains had the ability to dissolve phosphorus, potassium, or fix nitrogen. Through potted experiment, the three bacterial strains, 499G2 (Peribacillus simplex), 499G3 (Bacillus velezensis), and 499G4 (B. megaterium) have a positive effect on the growth of cultivated rice in addition to the resistance to rice blast. The contents of total nitrogen, total phosphorus, total potassium, indole acetic acid (IAA), and chlorophyll in plant leaves were increased. In addition, in the verification test of rice blast infection, the application of inoculants can significantly reduce the content of malondialdehyde (MDA), increase the content of soluble sugar, and increase the activity of plant antioxidant enzymes, which may thereby improve rice in resisting to rice blast.