Latest Articles[Objective] To reveal the mechanisms ofPseudomonas putida Y-9 in actively regulating the extracellular and intracellular pH homeostasis during ammonia oxidation.[Methods] Y-9 was cultured in the nitrification media with initial pH 7.19 and 9.40, respectively, for 48 h. Metabolomics was employed to compare the differential metabolites and predict dissociation constant (pKa) during the ammonia oxidation. Transcriptomics was employed to compare the genes regulating.[Results] In the medium with initial pH 7.19, Y-9 produced maltitol to raise extracellular pH, and up-regulated the expression of the genes related to deaminase, deiminase, and cation transport to maintain intracellular pH stability. In the medium with initial pH 9.40, Y-9 produced acidic substances such as 5-aminovaleric acid 3 and oxamic acid to lower extracellular pH and regulated the expression of the genes associated with NADH dehydrogenase, cytochromes, ATP synthase, and amino acid transport to maintain intracellular acidity.[Conclusion] This study revealed the novel phenomenon of Y-9's extracellular pH stabilizing capacity and investigated its intracellular pH homeostasis mechanism. The findings enrich our knowledge about microorganism-environment interactions, and provide a theoretical basis for further understanding the pH stabilization mechanism in microbial denitrification processes.
Gray mold caused byBotrytis cinerea is one of the major diseases affecting tomato production. The currently used fungicides are gradually restricted due to residues, pathogen resistance, and food safety. Therefore, screening out antagonistic microorganisms has gradually become an effective approach for the biocontrol of gray mold. [Objective] We screened out endophytic strains capable of endowing plants with disease resistance and promoting plant growth from tomato plants and evaluated their biocontrol potential, aiming to provide a theoretical basis for developing a new approach for the biocontrol of tomato gray mold.[Methods] The endophytic bacteria and fungi were isolated from different parts of tomato plants by the tissue culture method, and the candidate strains were preliminarily identified by 16S rRNA and ITS sequence analysis. The endophytes with antagonistic activity againstB.cinerea were screened by confrontation culture and fruit inoculationin vitro. Furthermore, we examined the abilities of the strain to secrete indole-3 acetic acid (IAA), protease, and siderophores and the promoting effects on the growth ofArabidopsis thaliana and tomato seedlings.[Results] A total of 72 endophytic bacterial strains and 31 endophytic fungal strains were isolated from different parts of tomato plants. An endophytic bacterium FQ-G3 with strong inhibitory activities against several pathogens was screened out and was identified asBacillus velezensis. FQ-G3 showed the inhibition rate of 80.93% againstB.cinereain vitro and inhibited the mycelial expansion on tomato fruitsin vivo. The strain could secrete IAA, protease, and siderophores, and promote the growth ofA.thaliana and tomato seedlings.[Conclusion] The endophytic strain FQ-G3 isolated from tomato plants endows plants with disease resistance and promotes plant growth, and thus can serve as a candidate for the prevention and control of gray mold. The findings enrich the tomato endophyte resources and provide support for the control of gray mold and the growth promotion of tomato.
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