Soil Augmentation with a Bacillus-Assemblage Drives Ecological Succession in the Rhizosphere and Improves Crop Growth Metrics.

Bacteria of the genus Bacillus are ubiquitous in the rhizosphere, where some species have been documented functioning as plant growth promoting bacteria (PGPB) or endophytes. In addition, many Bacillus are known to exhibit traits which may help to structure rhizosphere microbial communities, including the mobilization of recalcitrant nutrients and the production of antimicrobial peptides. In the present study, we used NGS-based 16s rRNA sequencing to examine ecological succession in soil microcosms subsequent to the addition of a commercially available soil amendment (BiOWiSH™ Crop) comprising a mixture of several bacillus species. Soil was collected from a working farm and treated with field-relevant levels of Bacillus-coated fertilizer and static cultured in the presence of growing corn. Results of 16s amplicon diversity assessments showed a repeatable increase in the abundance of known PGPBs such as Sphingomonas, Novosphingobium and Pseudomonas as well as a repeatable decrease in the abundance of known fungal phytopathogens such as Fusarium and Verticillium. Data did not support the hypothesis that Bacillus were proliferating and dominating the soil habitat. Endophyte assays showed the added bacillus concentrating in plant roots. Field trials conducted with the same commercially available product showed increased yield (10.3% increase for tomatoes and 15.1% increase for lettuce) and Brix score (7.5% increase for tomatoes and 7.3% for lettuce) in a variety of crops, consistent with the promotion of PGPB abundance in the rhizosphere. These results suggest that the capacity of a bacterial assemblage to initiate ecological succession in the rhizosphere may be an additional metric of interest when designing microbial amendments for use in commercial agronomy.