Development of bacterial bioformulations using response surface methodology

Abstract

Aim Bacterial consortia exhibiting plant growth promoting properties have emerged as a sustainable approach for crop improvement. As the main challenge associated with them is viability loss and performance under natural conditions, a robust approach for designing bioformulation is needed. In this study, an efficient bioformulation was developed using spontaneous mutants of three bacterial strains for growth promotion of Cajanus cajan. Methods and results Optimization of additives for solid [carboxymethylcellulose (CMC), and glycerol) and liquid [polysorbate, CMC, and polyvinyl pyrrolidone (PVP)] bioformulations was done by Response Surface Methodology using Central Composite Design. The stability of each bioinoculant in the formulation was assessed at 30°C and 4°C. The efficiency of the liquid bioformulation was checked in planta in sterile, and subsequently in non-sterile, soil. The maximum cell count was observed in solid bioformulation with 0.1 g L−1 CMC and 50% glycerol (8.10 × 108, 3.69 × 108, and 7.39 × 108 for Priestia megaterium, Azotobacter chroococcum, and Pseudomonas sp. SK3, respectively) and in liquid bioformulation comprising 1% PVP, 0.1 g L−1 CMC, and 0.025% polysorbate (8 × 109, 3.8 × 109, and 6.82 × 109 for Priestia megaterium, Azotobacter chroococcum, and Pseudomonas sp. SK3, respectively). The bioinoculants showed a higher viability (6 months) at 4°C compared to 30°C. Triple culture consortia enhanced plant growth in comparison to the control. The strains could be detected in soil till 45 days after sowing. Conclusions The study established a systematic process for developing a potent bioformulation to promote agricultural sustainability. Using mutant strains, the bioinoculants could be tracked. In planta assays revealed that the triple culture consortium out-performed mono and dual cultures in terms of impact on plant growth.