Adhesion of Rhodococcus bacteria to solid hydrocarbons and enhanced biodegradation of these compounds

Adhesive activities of hydrocarbon-oxidizing Rhodococcus bacteria towards solid hydrocarbons, effects of adhesion on biodegradation of these compounds by rhodococcal cells and adhesion mechanisms of Rhodococcus spp. were studied in this work. It was shown that efficiency of Rhodococcus cells' adhesion to solid n-alkanes and polycyclic aromatic hydrocarbons (PAHs) varied from 0.0 to 10.6·10⁶ CFU/cm². R. erythropolis IEGM 212 and R. opacus IEGM 262 demonstrated the highest (≥ 4.3·10⁶ CFU/cm²) adhesion. The percentage biodegradation of solid hydrocarbons (n-hexacosane and anthracene as model substrates) by Rhodococcus cells was 5 to 60% at a hydrocarbon concentration of 0.2% (w/w) after 9 days and strongly depended on cell adhesive activities towards these compounds (r ≥ 0.71, p < 0.05). No strict correlation between the adhesive activities of rhodococcal cells and physicochemical properties of bacteria and hydrocarbons was detected. Roughness of the cell surface was a definitive factor of Rhodococcus cell adhesion to solid hydrocarbons. Specific appendages with high adhesion force (≥ 0.6 nN) and elastic modulus (≥ 6 MPa) were found on the surface of Rhodococcus cells with high surface roughness. We hypothesized that these appendages participated in the adhesion process.