VOLATILE COMPOUNDS-MEDIATED PLANT GROWTH MODULATION by MICROBACTERIUM SP. STRAIN 15III

BURGOS HERRERA, GONZALO; DO NASCIMENTO, MAURO; CURATTI, LEONARDO

Encuentro; XVI Annual Meeting of the Argentinean Society for General Microbiology (SAMIGE); 2021

The present study was conducted to advance in the characterization of the plant growth-promotion properties of a native strain of Microbacterium sp. strain 15III, isolated earlier from a microalgal non-axenic culture. We observed previously a dose-dependent modulation of wheat seeds germination and sprouts growth form promotion (lower dose) to strong inhibition (higher dose) by inoculation of Microbacterium cells. Inoculation of wheat seedlings with this bacterium promoted leaves and roots dry weigh, and leaves length and chlorophyll content. In this study, to evaluate whether growth promotion would be at least mediated by volatile compounds, we conducted similar experiments in which the Petri dishes also contained a smaller dish containing Microbacterium sp. at different densities onto LB medium. The results suggested that the previously observed wheat growth-promotion could be mediated by volatile compound released by the bacterium. To further analyze whether this effect could be a general effect on plant-growth modulation, similar experiments were conducted with Arabidopsis thaliana, as a plant distantly related to wheat, and also a convenient experimental model. In these experiments, Microbaterium sp. exerted a similar dose-dependent seedlings growth modulation from stimulation to strong inhibition at higher bacterial densities. Similar experiments using chambered Petri dishes to isolate plants from bacteria, showed a similar dose-dependent plant growth modulation. Asymmetric placement of seedlings and bacteria in the dishes also showed a gradual effect according to the relative distance between the seedlings and the bacterial inoculation spots. A. thaliana seedlings exposed to this bacterium’s volatile compounds showed a dose-dependent more branched root-architecture and a significant increase in the number of root hairs. A preliminary gas chromatography coupled to mass spectrometry (GC-MS) analysis revealed the identity of the most abundant volatile compounds as small nitro-sulfur compounds such as dimethyl trisulphide and imidazolthione, which are strong candidates to be involved in the plant-growth modulating properties of Microbacterium sp. strain 15III.After immersion of A. thaliana flowers with a suspension of Microbacterium cells, the bacterium was consistently recovered from surface disinfected seeds and remained cultivable. It appeared that immersion in a higher cell density produced higher bacterial titles in the disinfected seeds. These results suggest a possible facultative endophytic life-style, and tolerance to the dehydrating conditions during seed development.