Phylogeny, Divergent Evolution, and Speciation of Sulfur-Oxidizing Acidithiobacillus Populations

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.

AI-driven pan-proteome analyses reveal insights into the biohydrometallurgical properties of Acidithiobacillia

Microorganism-mediated biohydrometallurgy, a sustainable approach for metal recovery from ores, relies on the metabolic activity of acidophilic bacteria. Acidithiobacillia with sulfur/iron-oxidizing capacities are extensively studied and applied in biohydrometallurgy-related processes. However, only 14 distinct proteins from Acidithiobacillia have experimentally determined structures currently available. This significantly hampers in-depth investigations of Acidithiobacillia's structure-based biological mechanisms pertaining to its relevant biohydrometallurgical processes. To address this issue, we employed a state-of-the-art artificial intelligence (AI)-driven approach, with a median model confidence of 0.80, to perform high-quality full-chain structure predictions on the pan-proteome (10,458 proteins) of the type strain Acidithiobacillia. Additionally, we conducted various case studies on de novo protein structural prediction, including sulfate transporter and iron oxidase, to demonstrate how accurate structure predictions and gene co-occurrence networks can contribute to the development of mechanistic insights and hypotheses regarding sulfur and iron utilization proteins. Furthermore, for the unannotated proteins that constitute 35.8% of the Acidithiobacillia proteome, we employed the deep-learning algorithm DeepFRI to make structure-based functional predictions. As a result, we successfully obtained gene ontology (GO) terms for 93.6% of these previously unknown proteins. This study has a significant impact on improving protein structure and function predictions, as well as developing state-of-the-art techniques for high-throughput analysis of large proteomic data.

Molecular Identification and Acid Stress Response of an Acidithiobacillus thiooxidans Strain Isolated from Rio Tinto (Spain)

Acidithiobacillus thiooxidans is of paramount importance in the development of biomining technologies. Being widely recognized as an extreme acidophile, extensive research has been dedicated to understanding its significant role in the extraction of several ores in recent years. However, there still exist significant molecular uncertainties surrounding this species. This study focuses on developing a taxonomic assignment method based on the sequencing of the 16S-5S rRNA cluster, along with a qPCR-based technology enabling precise growth determination. Additionally, an approach to understanding its response to acid stress is explored through RT-PCR and MALDI-TOF analysis. Our findings indicate that when subjected to pH levels below 1, the cell inhibits central (carbon fixation and metabolism) and energy (sulfur metabolism) metabolism, as well as chaperone synthesis, suggesting a potential cellular collapse. Nevertheless, the secretion of ammonia is enhanced to raise the environmental pH, while fatty acid synthesis is upregulated to reinforce the cell membrane.

Trade-off in genome turnover events leading to adaptive evolution of Microcystis aeruginosa species complex

BACKGROUND

Numerous studies in the past have expanded our understanding of the genetic differences of global distributed cyanobacteria that originated around billions of years ago, however, unraveling how gene gain and loss drive the genetic evolution of cyanobacterial species, and the trade-off of these evolutionary forces are still the central but poorly understood issues.

RESULTS

To delineate the contribution of gene flow in mediating the hereditary differentiation and shaping the microbial evolution, a global genome-wide study of bloom-forming cyanobacterium, Microcystis aeruginosa species complex, provided robust evidence for genetic diversity, reflected by enormous variation in gene repertoire among various strains. Mathematical extrapolation showed an 'open' microbial pan-genome of M. aeruginosa species, since novel genes were predicted to be introduced after new genomes were sequenced. Identification of numerous horizontal gene transfer's signatures in genome regions of interest suggested that genome expansion via transformation and phage-mediated transduction across bacterial lineage as an evolutionary route may contribute to the differentiation of Microcystis functions (e.g., carbohydrate metabolism, amino acid metabolism, and energy metabolism). Meanwhile, the selective loss of some dispensable genes at the cost of metabolic versatility is as a mean of adaptive evolution that has the potential to increase the biological fitness.

CONCLUSIONS

Now that the recruitment of novel genes was accompanied by a parallel loss of some other ones, a trade-off in gene content may drive the divergent differentiation of M. aeruginosa genomes. Our study provides a genetic framework for the evolution of M. aeruginosa species and illustrates their possible evolutionary patterns.

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.

Viruses Regulate Microbial Community Assembly Together with Environmental Factors in Acid Mine Drainage

Viruses are widespread in various ecosystems, and they play important roles in regulating the microbial community via host-virus interactions. Recently, metagenomic studies showed that there are extremely diverse viruses in different environments from the ocean to the human gut, but the influences of viral communities on microbial communities are poorly understood, especially in extreme environments. Here, we used metagenomics to characterize microbial communities and viral communities in acid mine drainage (AMD) and evaluated how viruses shape microbial community constrained by the harsh environments. Our results showed that AMD viral communities are significantly associated with the microbial communities, and viral diversity has positive correlations with microbial diversity. Viral community explained more variations of microbial community composition than environmental factors in AMD of a polymetallic mine. Moreover, we found that viruses harboring adaptive genes regulate a relative abundance of hosts under the modulation of environmental factors, such as pH. We also observed that viral diversity has significant correlations with the global properties of microbial cooccurrence networks, such as modularity. In addition, the results of null modeling analyses revealed that viruses significantly affect microbial community phylogeny and play important roles in regulating ecological processes of community assembly, such as dispersal limitation and homogenous dispersal. Together, these results revealed that AMD viruses are critical forces driving microbial network and community assembly via host-virus interactions. IMPORTANCE Viruses as mobile genetic elements play critical roles in the adaptive evolution of their hosts in extreme environments. However, how viruses further influence microbial community structure and assembly is still unclear. A recent metagenomic study observed diverse viruses unexplored in acid mine drainage, revealing the associations between the viral community and environmental factors. Here, we showed that viruses together with environmental factors can constrain the relative abundance of host and microbial community assembly in AMD of copper mines and polymetallic mines. Our results highlight the importance of viruses in shaping the microbial community from the individual host level to the community level.

Insights into Adaptive Mechanisms of Extreme Acidophiles Based on Quorum Sensing/Quenching-Related Proteins

Quorum sensing (QS) is a unique mechanism for microorganisms to coordinate their activities through intercellular communication, including four main types of autoinducer-1 (AI-1, namely, N-acyl homoserine lactone [AHL]), AI-2, AI-3, and diffusible signaling factor [DSF]) based on signaling molecules. Quorum quenching (QQ) enzymes can disrupt the QS phenomenon by inactivating signaling molecules. QS is proposed to regulate biofilm formation in extremely acidic environments, but the QS/QQ-related genomic features in most acidophilic bacteria are still largely unknown. Here, genome annotation of 83 acidophiles from the genera Acidithiobacillus, Leptospirillum, Sulfobacillus, and Acidiphilium altogether revealed the existence of AI-1, AI-3, DSF, and AhlD (AHL degradation enzyme). The conservative investigation indicated that some QS/QQ-related proteins harbored key residues or motifs, which were necessary for their activities. Phylogenetic analysis showed that LuxI/R (AI-1 synthase/receptor), QseE/F (two-component system of AI-3), and RpfC/G (two-component system of DSF) exhibited similar evolutionary patterns within each pair. Meanwhile, proteins clustered approximately according to the species taxonomy. The widespread Acidithiobacillus strains, especially A. ferrooxidans, processed AI-1, AI-3, and DSF systems as well as the AhlD enzyme, which were favorable for their mutual information exchange and collective regulation of gene expression. Some members of the Sulfobacillus and Acidiphilium without AHL production capacity contained the AhlD enzyme, which may evolve for niche competition, while DSF in Leptospirillum and Acidithiobacillus could potentially combine with the cyclic diguanylate (c-di-GMP) pathway for self-defense and niche protection. This work will shed light on our understanding of the extent of communication networks and adaptive evolution among acidophiles via QS/QQ coping with environmental changes.

IMPORTANCE Understanding cell-cell communication QS is highly relevant for comprehending the regulatory and adaptive mechanisms among acidophiles in extremely acidic ecosystems. Previous studies focused on the existence and functionality of a single QS system in several acidophilic strains. Four representative genera were selected to decipher the distribution and role of QS and QQ integrated with the conservative and evolutionary analysis of related proteins. It was implicated that intra- or intersignaling circuits may work effectively based on different QS types to modulate biofilm formation and energy metabolism among acidophilic microbes. Some individuals could synthesize QQ enzymes for specific QS molecular inactivation to inhibit undesirable acidophile species. This study expanded our knowledge of the fundamental cognition and biological roles underlying the dynamical communication interactions among the coevolving acidophiles and provided a novel perspective for revealing their environmental adaptability.

Genomic evolution of the class Acidithiobacillia: deep-branching Proteobacteria living in extreme acidic conditions

Members of the genus Acidithiobacillus, now ranked within the class Acidithiobacillia, are model bacteria for the study of chemolithotrophic energy conversion under extreme conditions. Knowledge of the genomic and taxonomic diversity of Acidithiobacillia is still limited. Here, we present a systematic analysis of nearly 100 genomes from the class sampled from a wide range of habitats. Some of these genomes are new and others have been reclassified on the basis of advanced genomic analysis, thus defining 19 Acidithiobacillia lineages ranking at different taxonomic levels. This work provides the most comprehensive classification and pangenomic analysis of this deep-branching class of Proteobacteria to date. The phylogenomic framework obtained illuminates not only the evolutionary past of this lineage, but also the molecular evolution of relevant aerobic respiratory proteins, namely the cytochrome bo₃ ubiquinol oxidases.

Application of Firefly Luciferase (Luc) as a Reporter Gene for the Chemoautotrophic and Acidophilic Acidithiobacillus spp

Acidithiobacillus spp. are the most active bacteria in bioleaching and bioremediation, because of their remarkable extreme environmental adaptabilities and unique metabolic characteristics. The researches on regulatory mechanisms of energy metabolism and stress resistance are critical for the understanding and application of Acidithiobacillus spp. However, the lack of an ideal reporter gene has become an obstacle for studying genes expression and regulatory mechanism in these chemoautotrophic bacteria. In this study, we reported the firefly luciferase as a reporter gene for Acidithiobacillus caldus (A. caldus) and created a firefly luciferase (Luc) reporter system. The Luc system was applied for the quantitative analysis of the transcription strength of the promoters of tetH gene and the feoA gene in A. caldus. Moreover, the regulating effect of ferric uptake regulator (Fur) on the feoP gene in A. caldus was determined using the Luc system. The Luc reporter system is not only used in the study of regulatory mechanism of A. caldus, but also applied in the researches of other Acidithiobacillus species. Therefore, this study provides a new useful tool for the studies on the molecular biological mechanism and synthetic biological modification of these chemoautotrophic bacteria, which would promote the industrial application of Acidithiobacillus spp.

Genome-Wide Analysis Reveals Genetic Potential for Aromatic Compounds Biodegradation of Sphingopyxis

Members of genus Sphingopyxis are frequently found in diverse eco-environments worldwide and have been traditionally considered to play vital roles in the degradation of aromatic compounds. Over recent decades, many aromatic-degrading Sphingopyxis strains have been isolated and recorded, but little is known about their genetic nature related to aromatic compounds biodegradation. In this study, bacterial genomes of 19 Sphingopyxis strains were used for comparative analyses. Phylogeny showed an ambiguous relatedness between bacterial strains and their habitat specificity, while clustering based on Cluster of Orthologous Groups suggested the potential link of functional profile with substrate-specific traits. Pan-genome analysis revealed that 19 individuals were predicted to share 1,066 orthologous genes, indicating a high genetic homogeneity among Sphingopyxis strains. Notably, KEGG Automatic Annotation Server results suggested that most genes pertaining aromatic compounds biodegradation were predicted to be involved in benzoate, phenylalanine, and aminobenzoate metabolism. Among them, β-ketoadipate biodegradation might be the main pathway in Sphingopyxis strains. Further inspection showed that a number of mobile genetic elements varied in Sphingopyxis genomes, and plasmid-mediated gene transfer coupled with prophage- and transposon-mediated rearrangements might play prominent roles in the evolution of bacterial genomes. Collectively, our findings presented that Sphingopyxis isolates might be the promising candidates for biodegradation of aromatic compounds in pollution sites.

Complete genome sequencing and comparative genomic analyses of Bacillus sp. S3, a novel hyper Sb(III)-oxidizing bacterium

BACKGROUND

Antimonite [Sb(III)]-oxidizing bacterium has great potential in the environmental bioremediation of Sb-polluted sites. Bacillus sp. S3 that was previously isolated from antimony-contaminated soil displayed high Sb(III) resistance and Sb(III) oxidation efficiency. However, the genomic information and evolutionary feature of Bacillus sp. S3 are very scarce.

RESULTS

Here, we identified a 5,436,472 bp chromosome with 40.30% GC content and a 241,339 bp plasmid with 36.74% GC content in the complete genome of Bacillus sp. S3. Genomic annotation showed that Bacillus sp. S3 contained a key aioB gene potentially encoding As (III)/Sb(III) oxidase, which was not shared with other Bacillus strains. Furthermore, a wide variety of genes associated with Sb(III) and other heavy metal (loid) s were also ascertained in Bacillus sp. S3, reflecting its adaptive advantage for growth in the harsh eco-environment. Based on the analysis of phylogenetic relationship and the average nucleotide identities (ANI), Bacillus sp. S3 was proved to a novel species within the Bacillus genus. The majority of mobile genetic elements (MGEs) mainly distributed on chromosomes within the Bacillus genus. Pan-genome analysis showed that the 45 genomes contained 554 core genes and many unique genes were dissected in analyzed genomes. Whole genomic alignment showed that Bacillus genus underwent frequently large-scale evolutionary events. In addition, the origin and evolution analysis of Sb(III)-resistance genes revealed the evolutionary relationships and horizontal gene transfer (HGT) events among the Bacillus genus. The assessment of functionality of heavy metal (loid) s resistance genes emphasized its indispensable role in the harsh eco-environment of Bacillus genus. Real-time quantitative PCR (RT-qPCR) analysis indicated that Sb(III)-related genes were all induced under the Sb(III) stress, while arsC gene was down-regulated.

CONCLUSIONS

The results in this study shed light on the molecular mechanisms of Bacillus sp. S3 coping with Sb(III), extended our understanding on the evolutionary relationships between Bacillus sp. S3 and other closely related species, and further enriched the Sb(III) resistance genetic data sources.

Functional role of bloom-forming cyanobacterium Planktothrix in ecologically shaping aquatic environments

Diverse metabolic behaviors endow microorganisms with various ecological functions, and metabolic activities of microbial species may affect the environmental conditions of their habitats. In this study, genome-guided analysis of Planktothrix spp. first divided these strains into six distinct groups, and comparisons of Planktothrix genomes revealed the inter- and intra-species variation. Prediction of central metabolism showed the functional diversity with regard to uptake of carbon, nitrogen, and sulfur sources. As the carbon-fixing microorganisms, Planktothrix isolates played a critical role in transforming the atmospheric carbon into organic carbon-the waterbodies' pool of available carbon. Diazotrophic lifestyle in certain Planktothrix strains may provide valuable avenues for supporting the equilibrium community. Furthermore, genome mining supported the exploration of biosynthetic gene clusters dedicated to cyanobacterial natural products, mainly including non-ribosomal peptide, polyketide, cyanobactin, and microviridin. Notably, some Planktothrix strains had the potential to non-ribosomally synthesize the microcystin (MC), a potent cyclic heptapeptide toxin, and MC-mediated cycling might strengthen the association between MC-producing and MC-degrading microorganisms. In short, genome-wide study of Planktothrix strains advances our current understanding of their metabolic potential and especially ecological roles in shaping natural environments.

Insights into ecological roles and potential evolution of Mlr-dependent microcystin-degrading bacteria

Over decades many studies have focused on the biodegradation of microcystins (MCs), and some Mlr-dependent MC-degrading bacteria were recorded, but the ecological functions, metabolic traits, and potential evolution of these organisms remain poorly understood. In this study, 16S rRNA-based phylogeny unraveled a wide range of genetic diversity across bacterial lineage, accompanied by re-evaluation of taxonomic placement of some MC-degrading species. Genome-wide comparison showed that considerable genes unique in individual organisms were identified, suggesting genetic differentiation among these Mlr-dependent MC-degrading bacteria. Notably, analyses of metabolic profiles first revealed the presence of functional genes involved in phenylacetate biodegradation in the specialized genomic regions, and mlr gene cluster was located around the neighborhood. The identification of transposable elements further indicated that these genomic regions might undergo horizontal gene transfer events to recruit novel functionalities, suggesting an adaptive force driving genome evolution of these organisms. In short, phylogenetic and genetic content analyses of Mlr-dependent MC-degraders shed light on their metabolic potential, ecological roles, and bacterial evolution, and expand the understanding of ecological status of MCs biodegradation.

Complete Genome Sequence of Acidithiobacillus Ferrooxidans YNTRS-40, a Strain of the Ferrous Iron- and Sulfur-Oxidizing Acidophile

Acidithiobacillus ferrooxidans YNTRS-40 (A. ferrooxidans) is a chemolithoautotrophic aerobic bacterium isolated from Tengchong hot springs, Yunnan Province, China, with a broad growth pH range of 1.0–4.5. This study reports the genome sequence of this strain and the information of genes related to the adaptation of diverse stresses and the oxidation of ferrous iron and sulfur. Results showed that YNTRS-40 possesses chromosomal DNA (3,209,933-bp) and plasmid DNA (47,104-bp). The complete genome of 3,257,037-bp consists of 3,349 CDS genes comprising 6 rRNAs, 52 tRNAs, and 6 ncRNAs. There are many encoded genes associated with diverse stresses adaptation and ferrous iron and sulfur oxidation such as rus operon, res operon, petI, petII, sqr, doxDA, cydAB, and cyoABCD. This work will provide essential information for further application of A. ferrooxidans YNTRS-40 in industry.