Transposition of IS elements induced by electroporation of suicide plasmid in Acidithiobacillus caldus

Screening and identification of functional bacterial attachment genes in aerobic granular sludge

The screening and identification of attachment genes is important to exploring the formation mechanism of biofilms at the gene level. It is helpful to the development of key culture technologies for aerobic granular sludge (AGS). In this study, genome-wide sequencing and gene editing were employed for the first time to investigate the effects and functions of attachment genes in AGS. With the help of whole-genome analysis, ten attachment genes were screened from thirteen genes, and the efficiency of gene screening was greatly improved. Then, two attachment genes were selected as examples to further confirm the gene functions by constructing gene-knockout recombinant mutants of Stenotrophomonas maltophilia; when the two attachment genes were knocked out, the attachment potential was reduced by 50.67% and 43.93%, respectively. The results provide a new theoretical principle and efficient method for the development of AGS from the perspective of attachment genes.

From Genes to Bioleaching: Unraveling Sulfur Metabolism in Acidithiobacillus Genus

Sulfur oxidation stands as a pivotal process within the Earth's sulfur cycle, in which Acidithiobacillus species emerge as skillful sulfur-oxidizing bacteria. They are able to efficiently oxidize several reduced inorganic sulfur compounds (RISCs) under extreme conditions for their autotrophic growth. This unique characteristic has made these bacteria a useful tool in bioleaching and biological desulfurization applications. Extensive research has unraveled diverse sulfur metabolism pathways and their corresponding regulatory systems. The metabolic arsenal of the Acidithiobacillus genus includes oxidative enzymes such as: (i) elemental sulfur oxidation enzymes, like sulfur dioxygenase (SDO), sulfur oxygenase reductase (SOR), and heterodisulfide reductase (HDR-like system); (ii) enzymes involved in thiosulfate oxidation pathways, including the sulfur oxidation (Sox) system, tetrathionate hydrolase (TetH), and thiosulfate quinone oxidoreductase (TQO); (iii) sulfide oxidation enzymes, like sulfide:quinone oxidoreductase (SQR); and (iv) sulfite oxidation pathways, such as sulfite oxidase (SOX). This review summarizes the current state of the art of sulfur metabolic processes in Acidithiobacillus species, which are key players of industrial biomining processes. Furthermore, this manuscript highlights the existing challenges and barriers to further exploring the sulfur metabolism of this peculiar extremophilic genus.

Insertion sequence contributes to the evolution and environmental adaptation of Acidithiobacillus

BACKGROUND

The genus Acidithiobacillus has been widely concerned due to its superior survival and oxidation ability in acid mine drainage (AMD). However, the contribution of insertion sequence (IS) to their biological evolution and environmental adaptation is very limited. ISs are the simplest kinds of mobile genetic elements (MGEs), capable of interrupting genes, operons, or regulating the expression of genes through transposition activity. ISs could be classified into different families with their own members, possessing different copies.

RESULTS

In this study, the distribution and evolution of ISs, as well as the functions of the genes around ISs in 36 Acidithiobacillus genomes, were analyzed. The results showed that 248 members belonging to 23 IS families with a total of 10,652 copies were identified within the target genomes. The IS families and copy numbers among each species were significantly different, indicating that the IS distribution of Acidithiobacillus were not even. A. ferrooxidans had 166 IS members, which may develop more gene transposition strategies compared with other Acidithiobacillus spp. What's more, A. thiooxidans harbored the most IS copies, suggesting that their ISs were the most active and more likely to transpose. The ISs clustered in the phylogenetic tree approximately according to the family, which were mostly different from the evolutionary trends of their host genomes. Thus, it was suggested that the recent activity of ISs of Acidithiobacillus was not only determined by their genetic characteristics, but related with the environmental pressure. In addition, many ISs especially Tn3 and IS110 families were inserted around the regions whose functions were As/Hg/Cu/Co/Zn/Cd translocation and sulfur oxidation, implying that ISs could improve the adaptive capacities of Acidithiobacillus to the extremely acidic environment by enhancing their resistance to heavy metals and utilization of sulfur.

CONCLUSIONS

This study provided the genomic evidence for the contribution of IS to evolution and adaptation of Acidithiobacillus, opening novel sights into the genome plasticity of those acidophiles.

Organic layer characteristics and microbial utilization of the biosulfur globules produced by haloalkaliphilic Thioalkalivibrio versutus D301 during biological desulfurization

The haloalkaliphilic genus Thioalkalivibrio, widely used in bio-desulfurization, can oxidize H₂S to S^o, which is excreted outside cells in the form of biosulfur globules. As by-product of bio-desulfurization, information on biosulfur globules is still very scant, which limits its high-value utilization. In this paper, the characteristics of biosulfur globules produced by Thioalkalivibrio versutus D301 and the possibility of cultivating sulfur-oxidizing bacteria as a high biological-activity sulfur source were studied. The sulfur element in the biosulfur globules existed in the form α-S₈, which was similar to chemical sulfur. The biosulfur globule was wrapped with an organic layer composed of polysaccharides and proteins. The composition of this organic layer could change. In the formation stage of biosulfur globules, the organic layer was dominated by polysaccharides, and in later stage, proteins became the main component. We speculated that the organic layer was mainly formed by the passive adsorption of organic matter secreted by cells. The existence of organic layer endowed biosulfur with better bioavailability. Compared with those found using chemical sulfur, the growth rates of Acidithiobacillus thiooxidans ATCC 19377^T, Thiomicrospira microaerophila BDL05 and Thioalkalibacter halophilus BDH06 using biosulfur increased several folds to an order of magnitude, indicating that biosulfur was a good sulfur source for cultivating sulfur-oxidizing bacteria.

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

Acidithiobacillaceae, 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, Acidithiobacillus 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 Acidithiobacillus spp. is regulated and how the flagellum affects the growth of these chemoautotrophic bacteria. In this study, we analyzed the flagellar gene clusters in Acidithiobacillus strains and uncovered the close relationship between flagella and the sulfur-oxidizing systems (Sox system). The σ²⁸ gene (rpoF) knockout and overexpression strains of Acidithiobacillus caldus were constructed. Scanning electron microscopy shows that A. caldus ΔrpoF cells lacked flagella, indicating the essential role of RpoF in regulating flagella synthesis in these chemoautotrophic bacteria. Motility analysis suggests that the deletion of rpoF resulted in the reduction of swarming capability, while this capability was enhanced in the rpoF overexpression strain. Both static cultivation and low concentration of energy substrates (elemental sulfur or tetrathionate) led to weak growth of A. caldus ΔrpoF cells. The deletion of rpoF 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.

Metals and minerals as a biotechnology feedstock: engineering biomining microbiology for bioenergy applications

Developing new feedstocks for the efficient production of biochemicals and biofuels will be a critical challenge as we diversify away from petrochemicals. One possible opportunity is the utilization of sulfide-based minerals in the Earth's crust. Non-photosynthetic chemolithoautotrophic bacteria are starting to be developed to produce biochemicals from CO₂ using energy obtained from the oxidation of inorganic feedstocks. Biomining of metals like gold and copper already exploit the native metabolism of these bacteria and these represent perhaps the largest-scale bioprocesses ever developed. The metabolic engineering of these bacteria could be a desirable alternative to classical heterotrophic bioproduction. In this review, we discuss biomining operations and the challenges and advances in the engineering of associated chemolithoautotrophic bacteria for biofuel production. The co-generation of biofuels integrated with mining operations is a largely unexplored opportunity that will require advances in fundamental microbiology and the development of new genetic tools and techniques for these organisms. Although this approach is presently in its infancy, the production of biochemicals using energy from non-petroleum mineral resources is an exciting new biotechnology opportunity.