AUTHOR=Wang Ya-Hui , Kong Wei-Liang , Zhu Mei-Ling , Dai Yun , Wu Xiao-Qin 

TITLE=Colonization by the Mycorrhizal Helper Bacillus pumilus HR10 Is Enhanced During the Establishment of Ectomycorrhizal Symbiosis Between Hymenochaete sp. Rl and Pinus thunbergii

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.818912

DOI=10.3389/fmicb.2022.818912

ISSN=1664-302X

ABSTRACT=<p>There are complex interactions between mycorrhizal helper bacteria (MHBs) and ectomycorrhizal (ECM) fungi, with MHBs promoting mycorrhizal synthesis and ECM fungi regulating plant rhizobacterial colonization, diversity, and function. In this study, to investigate whether the ECM fungus <italic>Hymenochaete</italic> sp. Rl affects the survival and colonization of the MHB strain <italic>Bacillus pumilus</italic> HR10 in the rhizosphere, the biomass of <italic>B. pumilus</italic> HR10 was measured in the rhizosphere and mycorrhizosphere. In addition, extracts of <italic>Hymenochaete</italic> sp. Rl and <italic>Pinus thunbergii</italic> were evaluated for their effect on <italic>B. pumilus</italic> HR10 colonization (growth, sporulation, biofilm formation, extracellular polysaccharide and extracellular protein contents, flagellar motility, and expression of colonization-related genes). The results showed that inoculation of <italic>Hymenochaete</italic> sp. Rl significantly increased the biomass of <italic>B. pumilus</italic> HR10 in the rhizosphere; however, while extracts of <italic>Hymenochaete</italic> sp. Rl and <italic>P. thunbergii</italic> did not affect the biomass or spore formation of HR10, they did affect its biofilm formation, extracellular polysaccharide and extracellular protein production, and flagellar motility. Furthermore, the addition of symbiont extracts affected the expression of chemotaxis-related genes in HR10. When the extracts were added separately, the expression of <italic>srf</italic> genes in HR10 increased; when the extracts were added simultaneously, the expression of the flagellin gene <italic>fliG</italic> in HR10 increased, but there was no significant effect on the expression of srf genes, consistent with the results on biofilm production. Thus, <italic>Hymenochaete</italic> sp. Rl and <italic>P. thunbergii</italic> roots had a positive effect on colonization by <italic>B. pumilus</italic> HR10 at the rhizosphere level through their secretions.</p>