In vitro and in silico investigation of the plant growth-promoting rhizobacteria from pepper (Piper nigrum L.)

The increase in awareness of the public to use inexpensive, safe, organic and environmentally friendly agricultural inputs makes plant growth-promoting rhizobacteria as one of the more attractive biological applications used to reduce or complement the use of synthetic agricultural inputs. In the present study, diligent investigation has been conducted in search of the most promising plant growthpromoting rhizobacteria from pepper (Piper nigrum L.) rhizosphere. As a result of the search, 14 rhizobacteria were isolated from the rhizosphere of the pepper plant (Piper nigrum L.). In vitro analyses showed that the isolates possessed many traits beneficial to agronomy, viz. biological nitrogen fixation, phosphate solubilisation and indole acetic acid (IAA) production. Analyses by 16S rRNA sequencing indicated that the isolates belonged to Acinetobacter radioresistens (UPMLH19), Bacillus cereus (UPMLH1, UPMLH13, UPMLH24, UPMLH41 and UPMLH42), Bacillus megaterium (UPMLH3 and UPMLH22), Bacillus subtilis (UPMLH5), Bacillus spp. (UPMLH8, UPMLH23, UPMLH34 and UPMLH43) and Leclercia sp. (UPMLH2). Phylogenetic analyses indicated that the newly isolated rhizobacteria from P. nigrum were from Firmicutes and Proteobacteria, with the former being more common. In the present study, computational methods were used to predict information within the small subunit 16S rRNA gene from B. cereus strain UPMLH24. The computational methods employed revealed that the small subunit 16S rRNA gene sequence from B.cereus strain UPMLH24 contained several open reading frames that encoded gamma-polyglutamic acid protein, lipoprotein, cytoplasmic protein and ribosomal protein S10. Computational predictions based on protein-protein identity classified seven phyla of organisms associated with small open reading frames of novel B.cereus strain UPMLH24. Plant bioassay technique was used to select the most promising isolates. Three vegetable crop species were used as test plants, namely mustard (Brassica ju