EXIGUOBACTERIUM SP. AS A BIOINOCULANT FOR PLANT-GROWTH PROMOTION AND FOR SELENIUM BIOFORTIFICATION STRATEGIES IN HORTICULTURAL PLANTS

MARFETAN, JORGE ARIEL; GALLO, ANA L.; MATTHIESS, WALTER; FARIAS, MARÍA E.; VELÉZ, MARÍA LAURA; PESCUMA, MICAELA; ORDOÑEZ, OMAR F.

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Sociedad Argentina de Microbiología General, SAMIGE

Exiguobacterium strains could be of biotechnological interest due to their diverse functions and applications. In sustainable agriculture, the substitution of chemical fertilizers by plant growth-promoting bacteria (PGPB) is desirable due to the reduction of costs and to the low environmental impact. On the other hand, Selenium (Se) is an essential trace element in humans but, in several countries, Se intake is less than the minimum daily requirement due to the low concentration of Se in soils. To deal with this, various Se bio-fortification strategies have been used. The aim of the present work was to analyse the plant-growth promoting capacity and the Se biotransformation ability of Exiguobacterium sp. (S17). Additionally, the beneficial effect of the application of selenised Exiguobacterium sp. (S17) was evaluated (Plant growth promotion, micronutrient bio-fortification and increase in antioxidants levels). Exiguobacterium sp. (S17) ability to enhance plant growth was first tested in the laboratory using Brassica juncea (indian mustard) and then in horticultural conditions using Beta vulgaris L. var Bressane (chard) and Lactuca sativa L. var Criolla verde (lettuce). Mustard seedlings with a double inoculation of Exiguobacterium sp. S17 had significantly greater dry weight than seedlings from the control groups. The same double Inoculation with the bacterial strain in chard produced an increase in leaf and root size and weight (fresh and dry). Regarding lettuce, the effect was observed only in leaves (Size and dry and fresh weight). Exiguobacterium sp. S17 was able to grow in media with Se, and the maximum Se incorporation was obtained when 160 mg/l of SE were added. The Se concentration in the cell pellets in selenised bacteria was 19.4 mg/l, while in the control cells 0.002 mg/lL. Irregular and spherical Selenium nanoparticles (SeNPs) were observed. Mustard plants inoculated with SeNPs showed a moderate increase in fresh weight whereas differences in dry weight were not observed. Besides the plant growth promotion effect, Se concentration in the SeNPs inoculated plants was at least 7.8 times greater than in the control ones. Additionally, an increase in the antioxidant capacity and the concentration of Fe, Mn, and Mg was also observed in SeNPs-inoculated plants. In conclusion, Exiguobacterium sp. (S17) showed two capabilities that make this bacterial strain a candidate to be applied in a bio-inoculant development. On one hand, produced a high plant-growth promotion in leafy greens such as chard and lettuce. On the other hand, Exiguobacterium sp. (S17) produce Se accumulation and bio-fortification of horticultural plants and the selenised bacteria can induce a higher accumulation of Se and other micronutrients. Finally, this bio-fortification is involved in the increase of the antioxidant capacity, and the improvement of the nutritional value of the horticultural plants.