Bacillus subtilis S16 and Paenibacillus mucilaginosus PM12 promoted chili pepper development by regulating rhizosphere microecology

Plant growth-promoting bacteria (PGPB) are increasingly used as bioinoculants to enhance crop performance, yet the mechanisms by which single and combined strains regulate chili pepper (Capsicum annuum L.) growth remain unclear. This study investigated the growth-promoting effects and mechanisms of Bacillus subtilis S16 and Paenibacillus mucilaginosus PM12, applied individually and in combination.

Field and hydroponic experiments assessed the impact of single and combined inoculations with B. subtilis S16 and P. mucilaginosus PM12 on chili pepper growth and yield. Production of growth-promoting substances, rhizosphere colonization by the two strains, microbial community structure, soil enzyme activities and soil nutrient availability were determined.

Both B. subtilis S16 and P. mucilaginosus PM12 produced indole-3-acetic acid, gibberellins, and zeatin riboside, and promoted seedling growth. In the field experiment, both strains efficiently colonized the rhizosphere and modulated rhizosphere microbial community composition. B. subtilis S16 significantly increased the relative abundances of Mortierella and Pseudaleuria in the rhizosphere fungal community by 42.11% and 137.51%, respectively, while decreasing the relative abundance of Neocosmospora by 96.41%. Moreover, Inoculation was associated with higher soil enzyme activities and more available phosphorus and potassium at the middle and late growth stages. These changes accompanied significant increases of chili pepper yield, with combined inoculation enhancing yield by 52.74% and capsaicin content by 2.12-fold.

This study demonstrates synergistic effects of combined B. subtilis S16 and P. mucilaginosus PM12 inoculation on chili pepper growth, yield, and fruit quality. These findings highlight its bioinoculant potential for sustainable chili pepper production.