Selection of cellulolytic aerobic spore-forming bacteria as an initial move to develop an inoculant that increases the degradation of plant biomass

TORRES, A.; PICCINETTI, C.; SAUKA, D.

Basilea

Conferencia; 1st International Electronic Conference on Agronomy; 2021

In a no tillage and continuous agriculture that include summer cereal crops in the rotation (as maize or sorghum) that takes place in the south and southeast of the Buenos Aires province, an emerging problem is the excessive accumulation of crop residues (stubbles rich in cellulose). Because of the climatic conditions of this area (low temperatures during crop fallow period), an accumulation of a plant biomass exists, which restricts the gradual degradation of these stubbles. This accumulation process causes impediments to the optimal planting dates of crops. The aim of this work was the selection of aerobic spore-forming bacteria able to degrade cellulose in order to develop an inoculant that increases the degradation rate of plant biomass. Eleven Bacillus thuringiensis and two unidentified strains were included in the study. Cellulose degrading ability of the strains was confirmed by a qualitative test on carboxy methyl cellulose (CMC) agar. A loopful from individual slants of the pure cultures were inoculated at the center of the plates and incubated at 29°C (five replicates). The cellulase activity of each strain was evaluated every 24 h during 5 days after staining with Congo red. Hydrolysis capacity (HC) was calculated. Paenibacillus xylanivorans A59 and distilled sterile water were included as positive and negative controls. Results showed that S310-1 was the most efficient cellulose-degrading bacterium with a HC index of 3.2 after 120 h of incubation. It was followed by strains S313-1 and A59, with HC indices of 2.4 and 2.2, suggesting that this magnitude of cellulose degradation is a function of the studied bacterium. Cellulase activity increased with incubation time. None of the B. thuringiensis strains showed a clearing halo zone on CMC agar. The aerobic spore-forming strains with high level of cellulase activity were selected because of screening.