Growth and Sporulation of Bacillus on Different Media

Abstract

Background: Culture-medium composition influences the growth and endospore formation of Bacillus isolates intended for biofertilizer development. Aim: This study examines the growth and sporulation of Bacillus recovered from the strawberry rhizosphere Methods: Three presumptive Bacillus isolates (E2, E3 and E6) were recovered from strawberry rhizosphere soil in Lembang, Indonesia. Isolate E2 was characterized using morphological and biochemical tests and 16S rRNA sequencing. It was subsequently cultured in tryptic soy broth (TSB) and sucrose-based broth (SBB) in 2 L bioreactors for 72 hours. Vegetative-cell and spore counts, pH, and electrical conductivity were monitored in duplicate. Results: Isolate E2 showed 99.86% sequence similarity to Bacillus sp. strain SZ057, with 100% query coverage. On day three, vegetative-cell counts were 13.79 ± 0.09 and 12.84 ± 0.27 log CFU/mL in TSB and SBB, respectively, while the spore counts were 8.20 ± 0.42 and 8.05 ± 0.21 log CFU/mL. The sporulation-rate were 59.46 ± 1.87% for TSB and 62.69 ± 0.23% for SBB. The biofertilizer in TSB maintained an acidity (pH) close to its initial value, whereas the pH in SBB declined during fermentation. Conclusion: TSB supported higher final cell and spore counts, while SBB yielded a higher sporulation rate. These laboratory findings inform medium selection for Bacillus liquid biofertilizer but do not yet establish biofertilizer efficacy in strawberry plants.