AUTHOR=Yang Chun-Long , Chen Xian-Ke , Wang Rui , Lin Jian-Qiang , Liu Xiang-Mei , Pang Xin , Zhang Cheng-Jia , Lin Jian-Qun , Chen Lin-Xu 

TITLE=Essential Role of σ Factor RpoF in Flagellar Biosynthesis and Flagella-Mediated Motility of Acidithiobacillus caldus

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.01130

DOI=10.3389/fmicb.2019.01130

ISSN=1664-302X

ABSTRACT=<p><italic>Acidithiobacillaceae</italic>, an important family of acidophilic and chemoautotrophic sulfur or iron oxidizers, participate in geobiochemical circulation of the elements and drive the release of heavy metals in mining associated habitats. Because of their environmental adaptability and energy metabolic systems, <italic>Acidithiobacillus</italic> spp. have become the dominant bacteria used in bioleaching for heavy metal recovery. Flagella-driven motility is associated with bacterial chemotaxis and bacterial responses to environmental stimuli. However, little is known about how the flagellum of <italic>Acidithiobacillus</italic> spp. is regulated and how the flagellum affects the growth of these chemoautotrophic bacteria. In this study, we analyzed the flagellar gene clusters in <italic>Acidithiobacillus</italic> strains and uncovered the close relationship between flagella and the sulfur-oxidizing systems (Sox system). The σ<sup>28</sup> gene (<italic>rpoF</italic>) knockout and overexpression strains of <italic>Acidithiobacillus caldus</italic> were constructed. Scanning electron microscopy shows that <italic>A. caldus</italic> Δ<italic>rpoF</italic> cells lacked flagella, indicating the essential role of RpoF in regulating flagella synthesis in these chemoautotrophic bacteria. Motility analysis suggests that the deletion of <italic>rpoF</italic> resulted in the reduction of swarming capability, while this capability was enhanced in the <italic>rpoF</italic> overexpression strain. Both static cultivation and low concentration of energy substrates (elemental sulfur or tetrathionate) led to weak growth of <italic>A. caldus</italic> Δ<italic>rpoF</italic> cells. The deletion of <italic>rpoF</italic> promoted bacterial attachment to the surface of elemental sulfur in static cultivation. The absence of RpoF caused an obvious change in transcription profile, including genes in flagellar cluster and those involved in biofilm formation. These results provide an understanding on the regulation of flagellar hierarchy and the flagellar function in these sulfur or iron oxidizers.</p>