Adhesion of Bacillus salmalaya and Bacillus amyloliquefaciens on oil palm kernel shell biochar: A physicochemical approach

Biochar emerges as a carrier for microorganisms in various biotechnological fields. The interest on this carbonaceous material stems from its physicochemical properties and microenvironment which can potentially harbor bacteria. We conducted a batch experiment to study the adhesion behavior of Bacillus salmalaya 139SI and Bacillus amyloliquefaciens NBRC 15535 via several adhesion kinetic models and isotherms. The adhesion of Bacillus salmalaya 139SI and Bacillus amyloliquefaciens NBRC 15535 on the oil palm kernel shell (OPKS) biochar was well described by the pseudo-second-order kinetics model (R2 > 0.90). The adhesion equilibrium of both bacteria on OPKS biochar was reached after 80 min with cell concentration of 108 CFU/g. Data fitting into Freundlich isotherm assuming that of cells have been adhered on the heterogenous surface of PKS biochar. Field Emission Scanning Electron Microscopy images shown the Bacillus spp. microcolony formation and possible network of biofilm structure on the biochar surface where the electron dispersive spectroscopy (EDS) analysis revealed the attachment of these bacteria occurred possibly on mineral-rich region on the biochar surface where the element is postulated to be responsible in enriching the microbes, improving their survival on the biochar. Several suggestions pertaining to the role of biochar and its potential to alter the biogeochemical processes for future studies are also included.