Three phenolic acid-degrading bacterial strains: screening, identification, and biological activities

Abstract:

[Background] Continuous planting of common crops can lead to the secretion of phenolic acid autotoxic substances in roots, which are the main factors causing soil-borne diseases and continuous cropping obstacles. [Objective] To mine the microorganisms capable of degrading benzoic acid secreted by crop roots, reduce the occurrence of soil-borne diseases, and reserve beneficial microbial resources. [Methods] We used benzoic acid as the sole carbon source in the inorganic salt medium to screen the strain resources of Wuliang Mountain and determined the degradation rate of benzoic acid by high-performance liquid chromatography. The plate confrontation test, tomato seed germination experiment, tomato seedling growth experiment, and pathogen (Fusarium wilt) inoculation experiment with tomato seedlings were carried out to examine the biological activities of the strains. The strains were identified based on morphological, physiological, and biochemical characteristics and 16S rRNA gene sequences. [Results] Four strains of Actinomycetes and three strains of bacteria with phenolic acid-degrading ability were screened from Wuliang Mountain. After culture in shake flasks for 72 h, the strains showed the benzoic acid-degrading rate of 100%, 99.83%, 99.89%, 99.87%, 64.91%, 56.92%, and 49.33%, respectively. Two Actinomycetes strains (YNK-FS0018 and YNK-FS0019) and one bacterial strain (YNK-FB0022) could make good use of benzoic acid. The treatments with the three strains alleviated the inhibitory effect of benzoic acid on tomato seed germination, with the seed germination rates of 73%, 73%, and 97%, the root length of 13.31, 13.04, and 14.56 cm, respectively. Furthermore, the three strains had broad-spectrum resistance to pathogens. YNK-FS0018 and YNK-FS0019 carried PKSII and NRPS, and YNK-FB0022 carried fenD, bioA, yndJ, ysnE, ituC, sboA, and srfAB. The results of pot experiments showed that strain YNK-FS0018 increased the plant height, above ground fresh weight, above ground dry weight, root weight, root length, and stem diameter by 53.40%, 67.50%, 57.50%, 73.50%, 77.28%, and 9.40%, respectively. The increases in the above indicators by YNK-FS0019 were 23.00%, 40.90%, 14.00%, 57.00%, 26.30%, and 16.80%, respectively. The increases by YNK-FB0022 were 24.50%, 44.70%, 26.40%, 75.10%, 98.00%, and 9.00%, respectively. The control effects of three strains on tomato Fusarium wilt were 87.10%, 74.18%, and 80.65%, respectively. YNK-FS0018, YNK-FS0019, and YNK-FB0022 were identified as Streptomyces blastmyceticus (Genbank accession number: OR523286), Streptomyces alboflavus (Genbank accession number: OR523289), and Bacillus halotolerans (Genbank accession number: OR523290), respectively. All the strains had the abilities of solubilizing organic phosphorus and zinc, secreting siderophores, and producing amylase and protease. [Conclusion] The three phenolic acid-degrading bacterial strains have the abilities of solubilizing organic phosphorus and zinc, secreting siderophores, and producing amylase and protease. They can significantly increase the plant height, stem thickness, root length, root weight, above ground fresh weight and above ground dry weight of tomato seedlings. Moreover, they demonstrate strong control effects on tomato Fusarium wilt, serving as the microbial resources for the biocontrol of soil-borne diseases.