Optimization of Liquid Media Amendments and Growth Kinetics of Plant Growth-promoting Microbial Strains for Consortium Development

Abstract

The increasing demand for sustainable agriculture has highlighted the importance of optimizing liquid biofertilizer formulations and understanding microbial growth kinetics to enhance the stability, viability, and effectiveness of plant growth-promoting bacteria. This study addresses the rising need for sustainable alternatives to chemical fertilizers by exploring the use of plant growth-promoting microorganisms (PGPMs). The experiment was conducted in 2022-23 in the Institute of Organic Farming, Dharwad. We standardized growth media for microbial isolates by incorporating various additives (polyethylene glycol, glycerol) and the antioxidant ascorbic acid. A total of 16 formulations were developed and evaluated. Formulations 3, 7, 10, and 16 showed significantly higher populations and were selected for further studies. The growth kinetics of the microbial strains PSA 7, PSA 5, PPFM 33, and LAB 75 were analysed to know the time taken to reach the maximum population by each microbial strain in specific media as well as a common medium (Luria broth- LB). It was also observed that all four microbial strains reached their respective highest population at 48, 48, 48 and 40 hrs respectively after incubation in their common broth medium. The population in terms of both CFU/ml and optical density values started to decline after 56th h for PSA 7, PSA 5, PPFM 33 while it was observed that 48h for LAB 75. Growth kinetics of these microbial strains suggested that higher growth could be achieved on a common (LB) media amended with protectants as compared to either respective selective media or LB without amendments. These findings underscore the potential for developing high-quality liquid biofertilizers, offering a promising pathway for sustainable agriculture and the reduction of harmful chemical fertilizers in crop production.