Isolation characterization and evaluation of potential plant growth promoting bacteria from the rhizosphere of coffea arabica L from kodagu district karnataka

Abstract

Agriculture is fundamental to food security and economic stability. The utilisation of newlineplant growth-promoting rhizobacteria (PGPR) an eco-friendly alternative to chemical newlinefertilisers is particularly promising as these microorganisms enhance nutrient newlineavailability, stimulate plant growth, and improve resistance to biotic and abiotic newlinestresses. This study aimed to isolate and characterise PGPR from the rhizosphere of newlineCoffea arabica L. in the Kodagu District of Karnataka, focusing on their potential as newlinebiofertilizers. Soil samples collected from ten different locations within Kamath Coffee newlineEstate led to the isolation of fourteen distinct bacterial colonies, labelled NJ01 to NJ14. These isolates were evaluated for various plant growth-promoting (PGP) traits like indole-3-acetic acid (IAA) siderophore and ammonia production, nitrogen fixation, newlinephosphate, and zinc solubilization and hydrogen cyanide (HCN) production. Further newlinestudies were carried out using 3 isolates with significant PGP traits. Enzyme activity newlineassays indicated that NJ01, NJ04, and NJ14 had positive results for protease, cellulase, newlineamylase, and catalase activity. These strains also displayed varying degrees of newlinehalotolerance, with NJ01, NJ04 and NJ14 tolerating up to 8%, 10% and 11% NaCl, newlinerespectively. Heavy metal tolerance tests revealed that NJ01 tolerated Pb up to 250 newlineµg/mL, NJ04 tolerated Pb up to 1500 µg/mL and Cd up to 50 µg/mL, and NJ14 tolerated Pb up to 1000 µg/mL and Hg up to 100 µg/mL. Polyhydroxyalkanoate (PHA) production was confirmed in all isolates, with NJ01 yielding the highest amount (6.4 g/L). The isolates exhibited significant antifungal and the 16S rRNA sequencing identified NJ01 as Bacillus albus (OP784795), NJ04 as Bacillus licheniformis (OM780221), and NJ14 as Bacillus subtilis (OM780222). A consortium was prepared after confirming the plant growth promoting abilities of these PGPR strains by carrying out an initial plant growth studies. The optimisation of media parameters was by using a two-factor interaction model.