Valorization of Agave Leaf Juice for Optimized Kocuria sediminis AS04 Production and Its Delivery via Immobilized Films to Mitigate Saline Stress in Capsicum annuum var. glabriusculum

Halotolerant plant growth-promoting bacteria offer a sustainable strategy to improve crop performance under saline conditions. This study evaluated Agave tequilana Weber var. Azul leaf juice was used as an alternative growth medium for Kocuria sediminis AS04, and the bacterium’s ability to alleviate salt stress in chiltepin (Capsicum annuum) was evaluated. The chiltepin seedlings were grown in a specialized chamber and exposed to higher salt levels (200, 400, and 600 mM NaCl) for 10 days. During this time, the protective effect of K. sediminis AS04, which was held in a polymer film, was examined. K. sediminis AS04 grew well in a medium containing 25% agave juice and urea, reaching a density of 1.3 × 1010 CFU mL−1. Compared with conventional Tryptic Soy Broth, the medium formulated from agave leaf juice and urea could reduce the cost per kilogram of biomass by approximately 4-fold. Under severe salinity stress, plants inoculated with immobilized K. sediminis at 600 mM NaCl exhibited the highest shoot biomass (0.31 g−1 plant), root length (50.7 mm), and proline accumulation (11.25 µmol g−1 fresh weight), whereas uninoculated plants displayed reduced biomass (0.16 g plant−1) and shorter roots (34.5 mm). At 600 mM NaCl, inoculation increased shoot biomass, root length, and plant survival by approximately 94%, 47%, and 200%, respectively, compared with uninoculated seedlings. This method values agro-industrial waste and enhances chiltepin performance under high-salinity conditions. It promotes sustainable production and helps create affordable inoculants for agricultural biotechnology.