Kosakonia radicincitans bSL2 as a PGPB: Effect on Lactuca sativa L. Seed Germination and Acute Toxicity Assessment in Rats

In response to the growing global demand for food and the need for sustainable and safe agricultural practices, this study evaluated the plant growth-promoting potential of the Kosakonia radicincitans bSL2 strain, its effect on Lactuca sativa L. seed germination, and its acute oral toxicity in Wistar rats. The objective was to assess its feasibility as an active ingredient in microbial-based biostimulants. K. radicincitans bSL2, originally isolated from apples in San Luis Province, Argentina, is preserved at the Industrial Microbiology Laboratory of the National University of San Luis. It exhibits typical plant growth-promoting rhizobacteria (PGPR) traits, including nitrogen fixation, phosphate solubilization, indole-3- acetic acid (IAA) production, and siderophore biosynthesis. The strain was successfully cultivated in a low-cost medium derived from brewing by-products, yielding high biomass. Its agronomic potential was tested by applying bacterial biomass to seeds of different lettuce cultivars under laboratory and nursery conditions. Results showed significant improvements in germination, with increases of 9–12% in laboratory assays and around 10% in nursery trials compared to controls. For toxicological evaluation, acute oral toxicity tests were performed in male and female Wistar rats using bacterial suspensions from 108 to 10¹² CFU/mL. No mortality, clinical signs, or significant changes in body weight or organ mass were detected. These findings indicate that K. radicincitans bSL2 is a safe and effective microbial agent with potential for agricultural biostimulant development. This is the first report describing the application of Kosakonia in this region.