Lobophorin Producing Endophytic Streptomyces olivaceus JB1 Associated With Maesa japonica (Thunb.) Moritzi & Zoll.

In this study, we focused on endophytes of Maesa japonica (Thunb.) Moritzi & Zoll. and the plant-microbe interaction at metabolite levels. We isolated seven endophytes associated with M. japonica (JB1-7), and focused on Streptomyces olivaceus JB1 because of antibacterial activities of its secondary metabolites. We confirmed lobophorin analogs production from the bacterial strain JB1 by using spectroscopic techniques such as NMR, UV, and LC/Q-TOF-MS. In the LC/MS system, thirteen reported lobophorin analogs and twelve unreported analogs were detected. Among metabolites, lobophorin A was clearly detected in the dried foliar residues of M. japonica which implies that JB1 resides in the host and accumulates its secondary metabolites likely interacting with the plant. Antimicrobial activity tests of the secondary metabolites against undesirable contaminants isolated from the external surface of M. japonica supported the host and microbe mutualistic relationship. In the meantime, lobophorin producing Streptomyces spp. were isolated from marine environments such as marine sediments, algae, corals, and sponges. As lobophorin producing Streptomyces is isolated commonly from marine environments, we conducted a saline water stress tolerance test with JB1 showing saline medium does not accelerate the growth of the bacterium.

Automated summary

This study focused on the endophytes of Maesa japonica and their interaction with the host plant at the metabolite level. Among the isolated endophytes, Streptomyces olivaceus JB1 was investigated for its antibacterial activities. Spectroscopic techniques confirmed the production of lobophorin analogs by JB1, and both reported and unreported analogs were detected. The presence of lobophorin A in the dried residues of M. japonica suggests that JB1 resides in the host and accumulates its secondary metabolites through interaction with the plant. Antimicrobial activity tests supported the mutualistic relationship between the host plant and the microbe. Additionally, lobophorin-producing Streptomyces spp. were also isolated from marine environments, and a saline water stress tolerance test showed that JB1 does not accelerate its growth in a saline medium.