Mg2+ Reduces Biofilm Quantity in Acidithiobacillus ferrooxidans through inhibiting Type IV Pili Formation

Abstract

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.