Mg2+ reduces biofilm quantity in Acidithiobacillus ferrooxidans through inhibiting Type IV pili formation.

Deping Tang, Qiyu Gao, Yang Zhao, Yang Li, Peng Chen, Jianping Zhou, Ruixiang Xu, Zhengrong Wu, Yuandong Xu, Hongyu Li

Bioleaching is a promising process for 350 million tons Jinchuan low grade pentlandite. But high concentration of Mg2+ is harmful to bioleaching microorganisms. Interestingly, biofilm formation can improve leaching rate. Thus, it is actual necessary to investigate the effect of Mg2+ stress on Acidithiobacillus ferrooxidans biofilms formatiom. In this study, we found that 0.1 and 0.5M Mg2+ stress significantly reduced the total biomass of biofilm in a dose-dependent manner. The observation results of EPS and bacteria using Confocal Laser Scanning Microscopy showed the biofilm became thinner and looser under Mg2+ stress. Whereas, 0.1 and 0.5M Mg2+ stress had no remarkable effect on the bacterial viability. The attachment rate of Acidithiobacillus ferrooxidans to pentlandite was reduced by Mg2+ stress. Furthermore, Sliding motility, twitching motility and the gene expression level of pilV and pilW were inhibited under Mg2+ stress. These results suggested Mg2+ reduced biofilm formation through inhibiting pilV and pilW gene expression, decreasing Type IV pili formation, and then attenuating the ability of attachment, subduing the active expansion of biofilms mediated by twitching motility. This study provided more information about the effect of Mg2+ stress on biofilm formation and may be useful for increasing the leaching rate in low grade pentlandit.