Insights into the complementation potential of the extreme acidophile's orthologue in replacing Escherichia coli hfq gene-particularly in bacterial resistance to environmental stress.

Acidithiobacillus caldus is a typical extreme acidophile widely used in the biohydrometallurgical industry, which often experiences extreme environmental stress in its natural habitat. Hfq, an RNA-binding protein, typically functions as a global regulator involved in various cellular physiological processes. Yet, the biological functions of Hfq derived from such extreme acidophile have not been extensively investigated. In this study, the recombinant strain Δhfq/Achfq, constructed by CRISPR/Cas9-mediated chromosome integration, fully or partially restored the phenotypic defects caused by hfq deletion in Escherichia coli, including impaired growth performance, abnormal cell morphology, impaired swarming motility, decreased stress resistance, decreased intracellular ATP and free amino acid levels, and attenuated biofilm formation. Particularly noteworthy, the intracellular ATP level and biofilm production of the recombinant strain were increased by 12.2% and 7.0%, respectively, compared to the Δhfq mutant. Transcriptomic analysis revealed that even under heterologous expression, AcHfq exerted global regulatory effects on multiple cellular processes, including metabolism, environmental signal processing, and motility. Finally, we established a potential working model to illustrate the regulatory mechanism of AcHfq in bacterial resistance to environmental stress.