Hydrodynamic Conditions Influence Bacterial Growth and Phenol Biodegradation of Strains with Different Morphology and Motility

Microorganisms are frequently exposed to flowing fluid, thus to investigate bacterial characteristics under different hydrodynamic conditions is of great importance in microbial ecology. This study characterized bacterial growth and phenol biodegradation of three strains, i.e., Microbacterium oxydans (rod-shaped, non-motile), Alcaligenes faecalis (rod-shaped, motile), and Staphylococcus haemolyticus (spherical, non-motile) in shake-flask cultures at various rotating speeds. For all the strains, a higher rotating speed always resulted in a shorter lag phase, indicating that the strains showed a superior adaptability under higher hydrodynamic conditions. The maximum specific growth rate of M. oxydans, A. faecalis, and S. haemolyticus increased rapidly with the increase of energy dissipation rate till the highest value of 0.386, 0.240, and 0.323 1/h and then decreased as the rotating speed further increased. The phenol biodegradation rate was also dependent on rotating speed, and the trends were consistent with the growth rate variations. A predictive model similar to Haldane model was proposed and was fitted well (R² > 0.913) with bacterial growth under different hydrodynamic conditions. According to the predictive model, the optimum hydrodynamic conditions for the growth of M. oxydans, A. faecalis, and S. haemolyticus were 3.099, 2.197, and 2.289 m²/s³, respectively. The results suggested that non-motile and rod-shaped bacteria were more dependent on hydrodynamic conditions than motile and spherical ones, which could be attributed to the discrepancies in bacterial morphology and motility. The results provide a better understanding on bacterial responses to various hydrodynamic conditions and could be further applied in the bioremediation of contaminated water.