Volatiles produced by Bacillus mojavensis RRC101 act as plant growth modulators and are strongly culture-dependent

Authors: RATH, MANISHA - University Of Georgia; Mitchell, Trevor; Gold, Scott

Submitted to: Microbiological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2017
Publication Date: 1/3/2018
Citation: Rath, M., Mitchell, T.R., Gold, S.E. 2018. Volatiles produced by Bacillus mojavensis RRC101 act as plant growth modulators and are strongly culture-dependent. Microbiological Research. 208:76-84.

Interpretive Summary: Volatile organic compounds (VOCs) produced by Plant Growth Promoting Rhizobacteria (PGPR) have recently been investigated due to their role in plant growth promotion and defense. Whereas some bacterial VOCs produced by strains of Bacillus subtilis and Bacillus amyloliquefaciens promote plant growth, other compounds inhibit plant growth or are phytotoxic. Bacillus mojavensis, a close relative of B. subtilis, is an endophytic bacterium of maize that has been shown to have antagonistic activity against the mycotoxigenic phytopathogen Fusarium verticillioides and growth promotion activity on maize seedlings. To investigate the growth promotion activity of B. mojavensis, Arabidopsis thaliana seedlings were grown on 1/2x Murashige & Skoog (MS) medium in divided Petri dishes while bacteria were grown either on 1/2x MS or nutrient agar (NA) medium, so that microbial volatiles reach the seedlings without other contact. Significant plant growth promotion in A. thaliana seedlings was observed when MS medium was used for bacterial growth. In contrast, phytotoxicity was observed with bacterial growth on NA medium. These results indicate that VOCs produced by B. mojavensis may act as plant growth modulators rather than just promoters. Both well documented as plant growth promoters; acetoin and 2, 3-butanediol were identified as being produced by B. mojavensis on growth promoting medium. On NA medium acetone/2-propanone may be a contributor to the phytotoxic effect.

Technical Abstract: Volatile organic compounds (VOCs) produced by Plant Growth Promoting Rhizobacteria have recently been investigated due to their role in plant growth promotion and defense. Whereas some bacterial VOCs like 3-hydroxy-2-butanone (acetoin) and 2,3-butanediol produced by strains of Bacillus subtilis and Bacillus amyloliquefaciens promote plant growth, others like hydrogen cyanide and 3-phenylpropionic acid are phytotoxic, inhibiting plant growth. Bacillus mojavensis, a close relative of B. subtilis, is an endophytic bacterium of maize that has been shown to have antagonistic activity against the mycotoxigenic phytopathogen Fusarium verticillioides and growth promotion activity on maize seedlings. To investigate the growth promotion activity of B. mojavensis, Arabidopsis thaliana seedlings were grown on 1/2x Murashige & Skoog (MS) medium in divided Petri dishes while bacteria were grown either on 1/2x MS or nutrient agar (NA) medium, so that only microbial volatiles reach the seedlings. Significant plant growth promotion in Arabidopsis seedlings was observed when 1/2x MS medium was used for bacterial growth. In contrast, phytotoxicity was observed with bacterial growth on NA medium. These results indicate that VOCs produced by B. mojavensis may act as plant growth modulators rather than just promoters. Using Solid Phase Microextraction (SPME) coupled with GC-MS, the plant growth promoting compounds acetoin and 2, 3-butanediol were both identified as being produced by B. mojavensis on growth promoting 1/2x MS medium. In contrast while no phytotoxic VOC was conclusively identified from B. mojavensis on NA medium, detection of relatively high levels of acetone/2-propanone indicates its possible contribution to Arabidopsis phytotoxicity.