AUTHOR=Gong Huiling , Jiang Wenxiao , Yang Yang , Zhang Yue , Chen Xufei , Li Wei , Yang Panlei , Wang Zhenshuo , Wang Qi , Li Yan 

TITLE=Cyclic di-GMP regulates bacterial colonization and further biocontrol efficacy of Bacillus velezensis against apple ring rot disease via its potential receptor YdaK

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1034168

DOI=10.3389/fmicb.2022.1034168

ISSN=1664-302X

ABSTRACT=<p><italic>Bacillus</italic> species are among the most investigated beneficial bacteria and widely used in agricultural systems as biological control agents. Its biocontrol efficacy is controlled by diverse regulators. Cyclic diguanylate (c-di-GMP) is a nearly universal second messenger in bacteria and modulates various important physiological processes, including motility, biofilm formation, antifungal antibiotic production and host colonization. However, the impact of c-di-GMP on biocontrol efficacy of beneficial bacteria is unknown. <italic>Bacillus velezensis</italic> PG12 is an effective biocontrol strain against apple ring rot disease caused by <italic>Botryosphaeria dothidea</italic>. In this study, the contribution of c-di-GMP to biocontrol efficacy of <italic>B. velezensis</italic> PG12 was investigated. Deletion of single gene encoding diguanylate cyclase or phosphodiesterase did not affect its biocontrol efficacy against apple ring rot. However, artificial modulation of c-di-GMP level in the cells leads to a significant change of biocontrol efficacy, suggesting that c-di-GMP positively regulates biocontrol efficacy of <italic>B. velezensis</italic> PG12 against apple ring rot disease. More evidences indicate that c-di-GMP does not affect the antagonistic activity of <italic>B. velezensis</italic> PG12 against <italic>B. dothidea in vitro</italic> and <italic>in vivo</italic>, but positively regulates biofilm formation of <italic>B. velezensis</italic> PG12 and its colonization on apple fruits. Importantly, deletion of <italic>ydaK</italic> could rescue the inhibition of biofilm formation, bacterial colonization and biocontrol efficacy caused by low c-di-GMP level, indicating that YdaK is the potential c-di-GMP receptor to regulate biofilm formation, colonization and effective biological control. However, YdaK did not affect the antagonistic activity of <italic>B. velezensis</italic> PG12 against <italic>B. dothidea</italic>. Based on these findings, we propose that c-di-GMP regulates biofilm formation, subsequently the bacterial colonization on apple fruits and thus biocontrol efficacy of <italic>B. velezensis</italic> through its receptor YdaK. This is the first report showing that c-di-GMP plays a role in biocontrol efficacy of beneficial bacteria.</p>