Bacterial endophytes of brassica crops as pathogens antagonists through the production of antimicrobial compounds

DUHALDE MA; SOLMI L; ROSSI FR; RUIZ OA; GÁRRIZ A; ROMERO FM

Congreso; V Congreso Argentino de Microbiología Agrícola y Ambiental; 2021

Many endophytic bacteria colonize host tissues internally without causing damage, in some cases, they promote plant growth and confer protection against pathogens. One of the mechanisms involved in the later is the production of antimicrobial compounds. This work aimed to characterize bacterial endophytes from different brassica crops, and to analyze their antagonistic properties against phytopathogens. For the isolation of bacterial endophytes, leaves samples were taken from three brassica crops (cabagge, broccoli and Brussel sprouts) grown in horticulture farms. Leaves from these crops were surface sterilized, homogenized and plated in rich medium. The collection obtained was screened in dual cultures with important pathogens such as Pectobacterium carotovorum, Xanthomonas campestris, Sclerotinia sclerotiorum and Leptosphaeria maculans. Also, plant-growth associated traits were tested (phosphate solubilization, indol acetic acid and siderophore production), as well as the production of volatile compounds with antifungal activity. Besides, whole supernatant as well as semi-purified fractions of these isolates were tested for antimicrobial activity. Selected isolates were identified by sequencing the 16S rRNA gene. A total of 81 endophytes were isolated from the brassica crops. Based on their ability to inhibit different pathogens in dual culture assays or the activation of plant-growth promoting mechanisms, three isolates (Bru13, Bro5 and Bro11) were selected and identified. Bru13 belongs to Pantoea genus, closely related to the specie P. agglomerans. While both, Bro5 and Bro11, belongs to Bacillus genus, Bro5 clustered with B. amyloliquefaciens and Bro11 with B. subtilis. The cell-free supernatant of these isolates inhibited the growth of P. carotovorum, X. campestris, S. sclerotiorum and L. maculans. The most drastic effect was observed with the supernatant of Bro5 and Bro11 showing inhibition rates ranging from 40 to 100%. To explore the nature of the antimicrobial compounds, different semi-purifications were performed to obtain peptide, secondary metabolites and lipopeptides fractions. Peptide fractions were the most effective, followed by the secondary metabolites? ones. In turn, the lipopeptide fraction did not show antimicrobial activity. Peptide fractions from Bro5 was the most effective against bacteria and fungi reaching a 100% inhibition. Finally, we evaluated the antifungal activity of volatile compounds produced by these isolates. In this way, all three isolates released volatile compounds that inhibited the growth of S. sclerotiorum and L. maculans by 50-80%. In conclusion, the isolates analyzed here exhibit a combination of beneficial traits related to biocontrol and growth promotion activities. Moreover, their ability to release compounds with antimicrobial activity, allow their use as bio-factories to produce new compounds aiming to control plant diseases in a more sustainable way avoiding the use of traditional agrochemicals.