EVALUATION OF THE POTENTIAL AGRONOMIC USE OF DIFFERENT Bacillus STRAINS ISOLATED OF WHEAT (Triticum aestivum) RHIZOSPHERE

OLIVELLA, LAURA; BARENGO, P. B; TROD, B.S; MARELLI, B; FIGUEROA, S.A; TORRES MANNO, MARIANO ALBERTO; PETITTI, TOMAS; ESPARIZ, MARTÍN; DAURELIO, LUCAS DAMIAN

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Sociedad Argentina de Microbiología General (SAMIGE)

The rhizosphere supports a vastly diversified microbial community, including microorganismcapable to regulate the development and activity of plant, with potential impact in the yieldimprove in crops. Wheat is the main produced wintry crop in our country. Previously, a novelgroup of Bacillus strains were isolated from wheat rhizosphere some of which, used individually,demonstrated the ability of promote plant growth, including an enhancement of yield. However,in order to be used in formulations, these Bacillus strains should not have cytotoxicity, and inorder to be combined, they should be compatible with each other. In this context, the aim of thiswork was to evaluate the compatibility between B. cereus (ZAV-W77), B. velezensis (ZAV-W70)and B. megaterium (ZAV-W64) strains and their possible cytotoxic effect on eukaryotic cells. Inorder to analyze their compatibility, growth curves were made with BioTek Synergy ® equipmentin plates of 96 wells, where ZAV-W77, ZAV-W70 and ZAV-W64 were combined with the filtratedsupernatant (FS) of the other two, FS-77, FS-70 and FS-64 respectively. To obtain the FS, thestrains were growth in dextrose potato medium (PD) at 28 °C 48 h, and then filtrated with sterilesyringe filters of 0.2 μm Minisart®. The assay was made by triplicate and for tree dilutions inLuria Bertani medium (LB)for each filtrated supernatant (1/2; 1/4 and 1/8) and the equipmentwas set to measure each 20 minutes at 30 °c for 16 hours. The negative control of growth was amixture of each filtered supernatant with LB, and the positive control was a mixture of asuspension of each strain (10 8 UFC/ml) and LB. No growth inhibition was observed of strainsZAV-W64 or ZAV-W70 when different dilutions of FS-70 or FS-64 were added, and no inhibitionwas observed for ZAV-W77 and ZAV-W70 whit different dilutions of FS-70 or FS-77,respectively. In contrast, even when Zav77 was not inhibited bay FS64, a strong growthinhibition of B. megaterium ZAV-W64 strain was observed in liquid medium when it was culturedin the presence of FS-77 even at 1/8 dilution, Also, tests were carried out in Potato DextroseAgar medium where it was observed that both bacteria affect their growth reciprocally. On theother hand, to determine the citotoxity an assay was performed using CHO.K1 cells. 8000cells/well were seeded in complete Minimum Essential Medium (MEM). After incubation, theculture medium was removed from the wells and 1 vol of each of the dilutions of thesupernatants (SN) to be evaluated or the controls (Culture medium or hydrogen peroxide) after24 hs of incubation, the viability was observed. It was observed that 1/2 dilutions of ZAV-W77and ZAV-W70 supernatants showed a decrease in viability compared to culture mediumdilutions, while this effect was not observed at greater dilutions. Supernatants of the B.megaterium ZAV64 strain did not show decreased viability at any dilution tested. In conclusion,these results suggest that, the three strains could be used in future biological formulations, ZAV-W64 and ZAV-W70 individually or combined, while Zav77 was incompatible with Zav64 andshould be excluded.Key words: Rhizosphere, Bacillus, biological formulations