Mechanisms of biotin-regulated gene expression in microbes

Bacterial single-cell RNA sequencing captures biofilm transcriptional heterogeneity and differential responses to immune pressure

Biofilm formation is an important mechanism of survival and persistence for many bacterial pathogens. These multicellular communities contain subpopulations of cells that display metabolic and transcriptional diversity along with recalcitrance to antibiotics and host immune defenses. Here, we present an optimized bacterial single-cell RNA sequencing method, BaSSSh-seq, to study Staphylococcus aureus diversity during biofilm growth and transcriptional adaptations following immune cell exposure. BaSSSh-seq captures extensive transcriptional heterogeneity during biofilm compared to planktonic growth. We quantify and visualize transcriptional regulatory networks across heterogeneous biofilm subpopulations and identify gene sets that are associated with a trajectory from planktonic to biofilm growth. BaSSSh-seq also detects alterations in biofilm metabolism, stress response, and virulence induced by distinct immune cell populations. This work facilitates the exploration of biofilm dynamics at single-cell resolution, unlocking the potential for identifying biofilm adaptations to environmental signals and immune pressure.

Pathway and protein channel engineering of Bacillus subtilis for improved production of desthiobiotin and biotin

Biotin (vitamin B7) is a crucial cofactor for various metabolic processes and has significant applications in pharmaceuticals, cosmetics, and animal feed. Bacillus subtilis, a well-studied Gram-positive bacterium, presents a promising host for biotin production due to its Generally Recognized as Safe (GRAS) status, robust genetic tractability, and capacity for metabolite secretion. This study focuses on the metabolic engineering of B. subtilis to enhance biotin biosynthesis. Initially, the desthiobiotin (DTB) and biotin synthesis ability of different B. subtilis strains were evaluated to screen for suitable chassis cells. Subsequently, the titers of DTB and biotin were increased to 21.6 mg/L and 2.7 mg/L, respectively, by relieving the feedback repression of biotin synthesis and deleting the biotin uptake protein YhfU. Finally, through engineering the access tunnel to the active site of biotin synthase (BioB) for reactants and modulating its expression, the biotin titer was increased to 11.2 mg/L, marking an 1130-fold improvement compared to the wild-type strain. These findings provide novel strategies for enhancing the production of DTB and improving the conversion efficiency of DTB to biotin.

Structural insights into BirA from Haemophilus influenzae, a bifunctional protein as a biotin protein ligase and a transcriptional repressor

Biotin is an essential coenzyme involved in various metabolic processes across all known organisms, with biotinylation being crucial for the activity of carboxylases. BirA from Haemophilus influenzae is a bifunctional protein that acts as a biotin protein ligase and a transcriptional repressor. This study reveals the crystal structures of Hin BirA in both its apo- and holo-(biotinyl-5'-AMP bound) forms. As a class II BirA, it consists of three domains: N-terminal DNA binding domain, central catalytic domain, and C-terminal SH3-like domain. The structural analysis shows that the biotin-binding loop forms an ordered structure upon biotinyl-5'-AMP binding. This facilitates its interaction with the ligand and promotes protein dimerization. Comparative studies with other BirA homologs from different organisms indicate that the residues responsible for binding biotinyl-5'-AMP are highly conserved. This study also utilized AlphaFold2 to model the potential heterodimeric interaction between Hin BirA and biotin carboxyl carrier protein, thereby providing insights into the structural basis for biotinylation. These findings enhance our understanding of the structural and functional characteristics of Hin BirA, highlighting its potential as a target for novel antibiotics that disrupt the bacterial biotin synthesis pathways.

A one-process production of completely biotinylated proteins in a T7 expression system

Streptavidin is a tetrameric protein with high specificity and affinity for biotin. The interaction between avidin and biotin has become a valuable tool in nanotechnology. In recent years, the site-specific biotin modification of proteins using biotin ligases, such as BirA, has attracted attention. This study established an in vivo method for achieving the complete biotinylation of target proteins using a single plasmid co-expressing BirA and its target proteins. Specifically, a biotin-modified protein was produced in Escherichia coli strain BL21(DE3) using a single plasmid containing genes encoding both BirA and a protein fused to BirA's substrate sequence, Avitag. This approach simplifies the production of biotinylated proteins in E. coli and allows the creation of various biotinylated protein types through gene replacement. Furthermore, the biotin modification rate of the obtained target protein could be evaluated using Native-PAGE without performing complicated isolation operations of biotinylated proteins. In Native-PAGE, biotin-modified proteins and unmodified proteins were confirmed as clearly different bands, and it was possible to easily derive the modification rate from the respective band intensities.

New Potent Sulfonamide-Based Inhibitors of S. aureus Biotin Protein Ligase

The key regulatory metabolic enzyme, biotin protein ligase (BPL), is an attractive target for the development of novel antibiotics against multi-drug-resistant bacteria, such as Staphylococcus aureus. Here we report the synthesis and assay of a new series of inhibitors (6-9) against S. aureus BPL (SaBPL), where a component sulfonamide linker was used to mimic the acyl-phosphate group of the natural intermediate biotinyl-5'-AMP (1). A pivotal correlation between the acidity of the central NH of the sulfonamide linker of 6-9 and in vitro inhibitory activity against SaBPL was observed. Specifically, sulfonylcarbamate 8, with its highly acidic sulfonyl central NH, as evaluated by 1H NMR spectroscopy, showed exceptional potency (K i = 10.3 ± 3.8 nM). Furthermore, three inhibitors demonstrated minimum inhibitory concentrations of 16-32 μg/mL against clinical methicillin-resistant S. aureus (MRSA) strains.

Bacterial single-cell RNA sequencing captures biofilm transcriptional heterogeneity and differential responses to immune pressure

Biofilm formation is an important mechanism of survival and persistence for many bacterial pathogens. These multicellular communities contain subpopulations of cells that display vast metabolic and transcriptional diversity along with high recalcitrance to antibiotics and host immune defenses. Investigating the complex heterogeneity within biofilm has been hindered by the lack of a sensitive and high-throughput method to assess stochastic transcriptional activity and regulation between bacterial subpopulations, which requires single-cell resolution. We have developed an optimized bacterial single-cell RNA sequencing method, BaSSSh-seq, to study Staphylococcus aureus diversity during biofilm growth and transcriptional adaptations following immune cell exposure. We validated the ability of BaSSSh-seq to capture extensive transcriptional heterogeneity during biofilm compared to planktonic growth. Application of new computational tools revealed transcriptional regulatory networks across the heterogeneous biofilm subpopulations and identification of gene sets that were associated with a trajectory from planktonic to biofilm growth. BaSSSh-seq also detected alterations in biofilm metabolism, stress response, and virulence that were tailored to distinct immune cell populations. This work provides an innovative platform to explore biofilm dynamics at single-cell resolution, unlocking the potential for identifying biofilm adaptations to environmental signals and immune pressure.

Advances and prospects in microbial production of biotin

Biotin, serving as a coenzyme in carboxylation reactions, is a vital nutrient crucial for the natural growth, development, and overall well-being of both humans and animals. Consequently, biotin is widely utilized in various industries, including feed, food, and pharmaceuticals. Despite its potential advantages, the chemical synthesis of biotin for commercial production encounters environmental and safety challenges. The burgeoning field of synthetic biology now allows for the creation of microbial cell factories producing bio-based products, offering a cost-effective alternative to chemical synthesis for biotin production. This review outlines the pathway and regulatory mechanism involved in biotin biosynthesis. Then, the strategies to enhance biotin production through both traditional chemical mutagenesis and advanced metabolic engineering are discussed. Finally, the article explores the limitations and future prospects of microbial biotin production. This comprehensive review not only discusses strategies for biotin enhancement but also provides in-depth insights into systematic metabolic engineering approaches aimed at boosting biotin production.

Genomic Insights into Paucibacter aquatile DH15, a Cyanobactericidal Bacterium, and Comparative Genomics of the Genus Paucibacter

Microcystis blooms threaten ecosystem function and cause substantial economic losses. Microorganism-based methods, mainly using cyanobactericidal bacteria, are considered one of the most ecologically sound methods to control Microcystis blooms. This study focused on gaining genomic insights into Paucibacter aquatile DH15 that exhibited excellent cyanobactericidal effects against Microcystis. Additionally, a pan-genome analysis of the genus Paucibacter was conducted to enhance our understanding of the ecophysiological significance of this genus. Based on phylogenomic analyses, strain DH15 was classified as a member of the species Paucibacter aquatile. The genome analysis supported that strain DH15 can effectively destroy Microcystis, possibly due to the specific genes involved in the flagellar synthesis, cell wall degradation, and the production of cyanobactericidal compounds. The pan-genome analysis revealed the diversity and adaptability of the genus Paucibacter, highlighting its potential to absorb external genetic elements. Paucibacter species were anticipated to play a vital role in the ecosystem by potentially providing essential nutrients, such as vitamins B7, B12, and heme, to auxotrophic microbial groups. Overall, our findings contribute to understanding the molecular mechanisms underlying the action of cyanobactericidal bacteria against Microcystis and shed light on the ecological significance of the genus Paucibacter.

Rumen and fecal microbiomes are related to diet and production traits in Bos indicus beef cattle

Background

Ruminants harbor a complex microbial community within their gastrointestinal tract, which plays major roles in their health and physiology. Brazil is one of the largest producers of beef in the world and more than 90% of the beef cattle herds are composed of pure and crossbred Nelore (Bos indicus). Despite its importance to the Brazilian economy and human feeding, few studies have characterized the Nelore microbiome. Therefore, using shotgun metagenomics, we investigated the impact of diet on the composition and functionality of the Nelore microbiome, and explored the associations between specific microbial taxa and their functionality with feed efficiency and methane emission.

Results

The ruminal microbiome exhibited significantly higher microbial diversity, distinctive taxonomic profile and variations in microbial functionality compared to the fecal microbiome, highlighting the distinct contributions of the microbiomes of these environments. Animals subjected to different dietary treatments exhibited significant differences in their microbiomes' archaeal diversity and in the abundance of 89 genera, as well as in the functions associated with the metabolism of components of each diet. Moreover, depending on the diet, feed-efficient animals and low methane emitters displayed higher microbial diversity in their fecal microbiome. Multiple genera were associated with an increase or decrease of the phenotypes. Upon analyzing the functions attributed to these taxa, we observed significant differences on the ruminal taxa associated with feed efficient and inefficient cattle. The ruminal taxa that characterized feed efficient cattle stood out for having significantly more functions related to carbohydrate metabolism, such as monosaccharides, di-/oligosaccharides and amino acids. The taxa associated with methane emission had functions associated with methanogenesis and the production of substrates that may influence methane production, such as hydrogen and formate.

Conclusion

Our findings highlight the significant role of diet in shaping Nelore microbiomes and how its composition and functionality may affect production traits such as feed efficiency and methane emission. These insights provide valuable support for the implementation of novel feeding and biotechnological strategies.

Effect of yhfS gene on Bt LLP29 antioxidant and UV ray resistance

BACKGROUND

Bacillus thuringiensis (Bt) is a widely used microbial insecticide. However, its persistence is limited because of ultraviolet (UV) rays or other environmental factors. The yhfS gene, which encodes acetyl-CoA acyltransferase, plays an important role in lipid transport and metabolism in many organisms. To explore whether it is related to the stress resistance of Bt LLP29, the yhfS gene knockout strain LLP29 Δ-yhfS and the complementary strain LLP29 R-yhfS were generated successfully by homologous recombination technology, and the related phenotypic changes were compared in this study.

RESULTS

Gene yhfS was found to be functional in response to UV radiation in Bt by comparing the survival rates of Bt LLP29 harboring yhfS or not under UV light. Enzyme activity assays of key enzymes showed the the Embden-Meyerhof-Parnas pathway was enhanced yet the tricarboxylic acid cycle as well as butanoate synthesis were repressed when the gene was deleted. At the same time, the amino acid content was decreased, but reduced nicotinamide adenine dinucleotide (NADH) and reactive oxygen species (ROS) content were increased. Most noteworthy, antioxidase (such as superoxide dismutase and peroxidase) activities and contents of some potent antioxidants (such as pyruvate, carotenoids and NADPH) were lower in LLP29 Δ-yhfS than in LLP29.

CONCLUSION

These tests revealed that the loss of the yhfS gene led to metabolic disorders and reduction of the antioxidant ability of Bt. Higher ROS level and lower anti-oxidative capacity might be responsible for the reduced UV resistance when the gene was deleted. These results not only greatly enrich understanding of the mechanism of Bt UV resistance, but also provide an important theoretical basis for Bt application. © 2023 Society of Chemical Industry.

Structural Study of Potent Triazole-Based Inhibitors of Staphylococcus aureus Biotin Protein Ligase

The rise of multidrug-resistant bacteria, such as Staphylococcus aureus, has highlighted global urgency for new classes of antibiotics. Biotin protein ligase (BPL), a critical metabolic regulatory enzyme, is an important target that shows significant promise in this context. Here we report the in silico docking, synthesis, and biological assay of a new series of N1-diphenylmethyl-1,2,3-triazole-based S. aureus BPL (SaBPL) inhibitors (8-19) designed to probe the adenine binding site and define whole-cell activity for this important class of inhibitor. Triazoles 13 and 14 with N1-propylamine and -butanamide substituents, respectively, were particularly potent with K i values of 10 ± 2 and 30 ± 6 nM, respectively, against SaBPL. A strong correlation was apparent between the K i values for 8-19 and the in silico docking, with hydrogen bonding to amino acid residues S128 and N212 of SaBPL likely contributing to potent inhibition.

Investigating the effect of the probiotic Lactobacillus plantarum and the prebiotic fructooligosaccharides on Pseudomonas aeruginosa metabolome, virulence factors and biofilm formation as potential quorum sensing inhibitors

Pseudomonas aeruginosa (P. aeruginosa) uses quorum sensing signaling (QS) molecules to control the expression of virulence factors and biofilm formation. In this study, the effects of the probiotic's (Lactobacillus plantarum (L. plantarum)) lysate and cell-free supernatant and the prebiotic (Fructooligosaccharides (FOS)) on the levels of P. aeruginosa QS molecules, virulence factors, biofilm density and metabolites were observed. These effects were investigated using exofactor assays, crystal violet and liquid chromatography-mass spectrometry (LC-MS)-based metabolomics approach. Results showed that in comparison to untreated P. aeruginosa, the L. plantarum cell-free supernatant (5%) and FOS (2%) significantly reduced the levels of the virulence factor pyoverdine (PVD) and several metabolites in the QS pathway including Pseudomonas autoinducer-2 (PAI-2). Metabolomics study revealed that the level of different secondary metabolites involved in the biosynthesis of vitamins, amino acids and the tricarboxylic acid (TCA) cycle were also affected. L. Plantarum was found to have a higher impact on the metabolomics profile of P. aeruginosa and its QS molecules compared to FOS. Lastly, a decrease in the formation of the P. aeruginosa biofilm was observed in a time-dependent pattern upon treatment with either cell-free supernatant of L. plantarum (5%), FOS (2%) or a combination of both treatments (5% + 2%). The latter showed the highest effect with 83% reduction in biofilm density at 72 h incubation. This work highlighted the important role probiotics and prebiotics play as potential QS inhibitors for P. aeruginosa. Moreover, it demonstrated the significant role of LC-MS metabolomics for investigating the altered biochemical and QS pathways in P. aeruginosa.

A New 1,2,3-Triazole Scaffold with Improved Potency against Staphylococcus aureus Biotin Protein Ligase

Staphylococcus aureus, a key ESKAPE bacteria, is responsible for most blood-based infections and, as a result, is a major economic healthcare burden requiring urgent attention. Here, we report in silico docking, synthesis, and assay of N1-diphenylmethyl triazole-based analogues (7-13) designed to interact with the entire binding site of S. aureus biotin protein ligase (SaBPL), an enzyme critical for the regulation of gluconeogenesis and fatty acid biosynthesis. The second aryl ring of these compounds enhances both SaBPL potency and whole cell activity against S. aureus relative to previously reported mono-benzyl triazoles. Analogues 12 and 13, with added substituents to better interact with the adenine binding site, are particularly potent, with K_i values of 6.01 ± 1.01 and 8.43 ± 0.73 nM, respectively. These analogues are the most active triazole-based inhibitors reported to date and, importantly, inhibit the growth of a clinical isolate strain of S. aureus ATCC 49775, with minimum inhibitory concentrations of 1 and 8 μg/mL, respectively.

dRNASb: a systems biology approach to decipher dynamics of host-pathogen interactions using temporal dual RNA-seq data

Infection triggers a dynamic cascade of reciprocal events between host and pathogen wherein the host activates complex mechanisms to recognise and kill pathogens while the pathogen often adjusts its virulence and fitness to avoid eradication by the host. The interaction between the pathogen and the host results in large-scale changes in gene expression in both organisms. Dual RNA-seq, the simultaneous detection of host and pathogen transcripts, has become a leading approach to unravelling complex molecular interactions between the host and the pathogen and is particularly informative for intracellular organisms. The amount of in vitro and in vivo dual RNA-seq data is rapidly growing, which demands computational pipelines to effectively analyse such data. In particular, holistic, systems-level, and temporal analyses of dual RNA-seq data are essential to enable further insights into the host-pathogen transcriptional dynamics and potential interactions. Here, we developed an integrative network-driven bioinformatics pipeline, dRNASb, a systems biology-based computational pipeline to analyse temporal transcriptional clusters, incorporate molecular interaction networks (e.g. protein-protein interactions), identify topologically and functionally key transcripts in host and pathogen, and associate host and pathogen temporal transcriptome to decipher potential between-species interactions. The pipeline is applicable to various dual RNA-seq data from different species and experimental conditions. As a case study, we applied dRNASb to analyse temporal dual RNA-seq data of Salmonella-infected human cells, which enabled us to uncover genes contributing to the infection process and their potential functions and to identify putative associations between host and pathogen genes during infection. Overall, dRNASb has the potential to identify key genes involved in bacterial growth or host defence mechanisms for future uses as therapeutic targets.

The Fusaric Acid Derivative qy17 Inhibits Staphylococcus haemolyticus by Disrupting Biofilm Formation and the Stress Response via Altered Gene Expression

Staphylococcus haemolyticus (S. haemolyticus) is the second most commonly isolated coagulase-negative staphylococcus (CoNS) in patients with hospital-acquired infections. It can produce phenol-soluble modulin (PSM) toxins and form biofilms. Compared with the wealth of information on Staphylococcus aureus and Staphylococcus epidermidis, very little is known about S. haemolyticus. There is an urgent need to find an effective preparation to combat the harm caused by S. haemolyticus infection. Chinese herbs have been utilized to cure inflammation and infectious diseases and have a long history of anticancer function in China. Here, we modified fusaric acid characterized from the metabolites of Gibberella intermedia, an endophyte previously isolated from Polygonum capitatum. This study shows that fusaric acid analogs (qy17 and qy20) have strong antibacterial activity against S. haemolyticus. In addition, crystal violet analyses and scanning electron microscopy observations demonstrated that qy17 inhibited biofilm formation and disrupted mature biofilms of S. haemolyticus in a dose-dependent manner. Additionally, it reduced the number of live bacteria inside the biofilm. Furthermore, the antibiofilm function of qy17 was achieved by downregulating transcription factors (sigB), transpeptidase genes (srtA), and bacterial surface proteins (ebp, fbp) and upregulating biofilm-related genes and the density-sensing system (agrB). To further elucidate the bacteriostatic mechanism, transcriptomic analysis was carried out. The following antibacterial mechanisms were uncovered: (i) the inhibition of heat shock (clpB, groES, groL, grpE, dnaK, dnaJ)-, oxidative stress (aphC)- and biotin response (bioB)-related gene expression, which resulted in S. haemolyticus being unable to compensate for various stress conditions, thereby affecting bacterial growth; and (ii) a reduction in the expression of PSM-beta (PSMβ1, PSMβ2, PSMβ3) toxin- and Clp protease (clpP, clpX)-related genes. These findings could have major implications for the treatment of diseases caused by S. haemolyticus infections. Our research reveals for the first time that fusaric acid derivatives inhibit the expression of biofilm formation-related effector and virulence genes of S. haemolyticus. These findings provide new potential drug candidates for hospital-acquired infections caused by S. haemolyticus.

Functional dissection and modulation of the BirA protein for improved autotrophic growth of gas-fermenting Clostridium ljungdahlii

Gas-fermenting Clostridium species can convert one-carbon gases (CO2 /CO) into a variety of chemicals and fuels, showing excellent application prospects in green biological manufacturing. The discovery of crucial genes and proteins with novel functions is important for understanding and further optimization of these autotrophic bacteria. Here, we report that the Clostridium ljungdahlii BirA protein (ClBirA) plays a pleiotropic regulator role, which, together with its biotin protein ligase (BPL) activity, enables an effective control of autotrophic growth of C. ljungdahlii. The structural modulation of ClBirA, combined with the in vivo and in vitro analyses, further reveals the action mechanism of ClBirA's dual roles as well as their interaction in C. ljungdahlii. Importantly, an atypical, flexible architecture of the binding site was found to be employed by ClBirA in the regulation of a lot of essential pathway genes, thereby expanding BirA's target genes to a broader range in clostridia. Based on these findings, molecular modification of ClBirA was performed, and an improved cellular performance of C. ljungdahlii was achieved in gas fermentation. This work reveals a previously unknown potent role of BirA in gas-fermenting clostridia, providing new perspective for understanding and engineering these autotrophic bacteria.

A division of labor between two biotin protein ligase homologs

Group I biotin protein ligases (BPLs) catalyze the covalent attachment of biotin to its cognate acceptor proteins. In contrast, Group II BPLs have an additional N-terminal DNA-binding domain and function not only in biotinylation but also in transcriptional regulation of genes of biotin biosynthesis and transport. Most bacteria contain only a single biotin protein ligase, whereas Clostridium acetobutylicum contains two biotin protein ligase homologs: BplA and BirA'. Sequence alignments showed that BplA is a typical group I BPL, whereas BirA' lacked the C-terminal domain conserved throughout extant BPL proteins. This raised the questions of why two BPL homologs are needed and why the apparently defective BirA' has been retained. We have used in vivo and in vitro assays to show that BplA is a functional BPL whereas BirA' acts as a biotin sensor involved in transcriptional regulation of biotin transport. We also successfully converted BirA' into a functional biotin protein ligase with regulatory activity by fusing it to the C-terminal domain from BplA. Finally, we provide evidence that BplA and BirA' interact in vivo.

Evolution of Wolbachia mutualism and reproductive parasitism: insight from two novel strains that co-infect cat fleas

Wolbachiae are obligate intracellular bacteria that infect arthropods and certain nematodes. Usually maternally inherited, they may provision nutrients to (mutualism) or alter sexual biology of (reproductive parasitism) their invertebrate hosts. We report the assembly of closed genomes for two novel wolbachiae, wCfeT and wCfeJ, found co-infecting cat fleas (Ctenocephalides felis) of the Elward Laboratory colony (Soquel, CA, USA). wCfeT is basal to nearly all described Wolbachia supergroups, while wCfeJ is related to supergroups C, D and F. Both genomes contain laterally transferred genes that inform on the evolution of Wolbachia host associations. wCfeT carries the Biotin synthesis Operon of Obligate intracellular Microbes (BOOM); our analyses reveal five independent acquisitions of BOOM across the Wolbachia tree, indicating parallel evolution towards mutualism. Alternately, wCfeJ harbors a toxin-antidote operon analogous to the wPip cinAB operon recently characterized as an inducer of cytoplasmic incompatibility (CI) in flies. wCfeJ cinB and three adjacent genes are collectively similar to large modular toxins encoded in CI-like operons of certain Wolbachia strains and Rickettsia species, signifying that CI toxins streamline by fission of large modular toxins. Remarkably, the C. felis genome itself contains two CI-like antidote genes, divergent from wCfeJ cinA, revealing episodic reproductive parasitism in cat fleas and evidencing mobility of CI loci independent of WO-phage. Additional screening revealed predominant co-infection (wCfeT/wCfeJ) amongst C. felis colonies, though fleas in wild populations mostly harbor wCfeT alone. Collectively, genomes of wCfeT, wCfeJ, and their cat flea host supply instances of lateral gene transfers that could drive transitions between parasitism and mutualism.

Biochemical characterisation of class III biotin protein ligases from Botrytis cinerea and Zymoseptoria tritici

Biotin protein ligase (BPL) is an essential enzyme in all kingdoms of life, making it a potential target for novel anti-infective agents. Whilst bacteria and archaea have simple BPL structures (class I and II), the homologues from certain eukaryotes such as mammals, insects and yeast (class III) have evolved a more complex structure with a large extension on the N-terminus of the protein in addition to the conserved catalytic domain. The absence of atomic resolution structures of any class III BPL hinders structural and functional analysis of these enzymes. Here, two new class III BPLs from agriculturally important moulds Botrytis cinerea and Zymoseptoria tritici were characterised alongside the homologue from the prototypical yeast Saccharomyces cerevisiae. Circular dichroism and ion mobility-mass spectrometry analysis revealed conservation of the overall tertiary and secondary structures of all three BPLs, corresponding with the high sequence similarity. Subtle structural differences were implied by the different thermal stabilities of the enzymes and their varied Michaelis constants for their interactions with ligands biotin, MgATP, and biotin-accepting substrates from different species. The three BPLs displayed different preferences for fungal versus bacterial protein substrates, providing further evidence that class III BPLs have a 'substrate validation' activity for selecting only appropriate proteins for biotinylation. Selective, potent inhibition of these three BPLs was demonstrated despite sequence and structural homology. This highlights the potential for targeting BPL for novel, selective antifungal therapies against B. cinerea, Z. tritici and other fungal species.

The Biotin Biosynthetic Pathway in Mycobacterium tuberculosis is a Validated Target for the Development of Antibacterial Agents

Mycobacterium tuberculosis, responsible for Tuberculosis (TB), remains the leading cause of mortality among infectious diseases worldwide from a single infectious agent, with an estimated 1.7 million deaths in 2016. Biotin is an essential cofactor in M. tuberculosis that is required for lipid biosynthesis and gluconeogenesis. M. tuberculosis relies on de novo biotin biosynthesis to obtain this vital cofactor since it cannot scavenge sufficient biotin from a mammalian host. The biotin biosynthetic pathway in M. tuberculosis has been well studied and rigorously genetically validated providing a solid foundation for medicinal chemistry efforts. This review examines the mechanism and structure of the enzymes involved in biotin biosynthesis and ligation, summarizes the reported genetic validation studies of the pathway, and then analyzes the most promising inhibitors and natural products obtained from structure-based drug design and phenotypic screening.

The DEAD-box RNA helicase CshA is required for fatty acid homeostasis in Staphylococcus aureus

Staphylococcus aureus is an opportunistic pathogen that can grow in a wide array of conditions: on abiotic surfaces, on the skin, in the nose, in planktonic or biofilm forms and can cause many type of infections. Consequently, S. aureus must be able to adapt rapidly to these changing growth conditions, an ability largely driven at the posttranscriptional level. RNA helicases of the DEAD-box family play an important part in this process. In particular, CshA, which is part of the degradosome, is required for the rapid turnover of certain mRNAs and its deletion results in cold-sensitivity. To understand the molecular basis of this phenotype, we conducted a large genetic screen isolating 82 independent suppressors of cold growth. Full genome sequencing revealed the fatty acid synthesis pathway affected in many suppressor strains. Consistent with that result, sublethal doses of triclosan, a FASII inhibitor, can partially restore growth of a cshA mutant in the cold. Overexpression of the genes involved in branched-chain fatty acid synthesis was also able to suppress the cold-sensitivity. Using gas chromatography analysis of fatty acids, we observed an imbalance of straight and branched-chain fatty acids in the cshA mutant, compared to the wild-type. This imbalance is compensated in the suppressor strains. Thus, we reveal for the first time that the cold sensitive growth phenotype of a DEAD-box mutant can be explained, at least partially, by an improper membrane composition. The defect correlates with an accumulation of the pyruvate dehydrogenase complex mRNA, which is inefficiently degraded in absence of CshA. We propose that the resulting accumulation of acetyl-CoA fuels straight-chained fatty acid production at the expense of the branched ones. Strikingly, addition of acetate into the medium mimics the cshA deletion phenotype, resulting in cold sensitivity suppressed by the mutations found in our genetic screen or by sublethal doses of triclosan.

DEAD-box RNA helicases are highly conserved proteins found in all domains of life. By acting on RNA secondary structures they determine the fate of RNA from transcription to degradation. Bacterial DEAD-box RNA helicases are not essential under laboratory conditions but are required for fitness and under stress conditions. Whereas many DEAD-box protein mutants display a cold sensitive phenotype, the underlying mechanisms have been studied only in few cases and found to be associated with ribosome biogenesis. We aimed here to elucidate the cold sensitivity of a cshA mutant in the Gram-positive opportunist pathogen Staphylococcus aureus. Our study revealed for the first time that part of the cold sensitivity is related to the inability of the bacterium to adapt the cytoplasmic membrane to lower temperatures. We propose that straight-chain fatty acid synthesis, reduced to sustain growth at lower temperature, is maintained due to inefficient turn-over of the pyruvate dehydrogenase mRNA, leading to elevated acetyl-CoA levels. This study allowed us to unravel at least in part the cold sensitive phenotype and to show that the pyruvate dehydrogenase activity plays an important function in the regulation of fatty acid composition of the membrane, a process that remains poorly understood in Gram-positive bacteria.

Comparative genomics of the genus Roseburia reveals divergent biosynthetic pathways that may influence colonic competition among species

Roseburia species are important denizens of the human gut microbiome that ferment complex polysaccharides to butyrate as a terminal fermentation product, which influences human physiology and serves as an energy source for colonocytes. Previous comparative genomics analyses of the genus Roseburia have examined polysaccharide degradation genes. Here, we characterize the core and pangenomes of the genus Roseburia with respect to central carbon and energy metabolism, as well as biosynthesis of amino acids and B vitamins using orthology-based methods, uncovering significant differences among species in their biosynthetic capacities. Variation in gene content among Roseburia species and strains was most significant for cofactor biosynthesis. Unlike all other species of Roseburia that we analysed, Roseburia inulinivorans strains lacked biosynthetic genes for riboflavin or pantothenate but possessed folate biosynthesis genes. Differences in gene content for B vitamin synthesis were matched with differences in putative salvage and synthesis strategies among species. For example, we observed extended biotin salvage capabilities in R. intestinalis strains, which further suggest that B vitamin acquisition strategies may impact fitness in the gut ecosystem. As differences in the functional potential to synthesize components of biomass (e.g. amino acids, vitamins) can drive interspecies interactions, variation in auxotrophies of the Roseburia spp. genomes may influence in vivo gut ecology. This study serves to advance our understanding of the potential metabolic interactions that influence the ecology of Roseburia spp. and, ultimately, may provide a basis for rational strategies to manipulate the abundances of these species.

Advanced Resistance Studies Identify Two Discrete Mechanisms in Staphylococcus aureus to Overcome Antibacterial Compounds that Target Biotin Protein Ligase

Biotin protein ligase (BPL) inhibitors are a novel class of antibacterial that target clinically important methicillin-resistant Staphylococcus aureus (S. aureus). In S. aureus, BPL is a bifunctional protein responsible for enzymatic biotinylation of two biotin-dependent enzymes, as well as serving as a transcriptional repressor that controls biotin synthesis and import. In this report, we investigate the mechanisms of action and resistance for a potent anti-BPL, an antibacterial compound, biotinyl-acylsulfamide adenosine (BASA). We show that BASA acts by both inhibiting the enzymatic activity of BPL in vitro, as well as functioning as a transcription co-repressor. A low spontaneous resistance rate was measured for the compound (<10⁻⁹) and whole-genome sequencing of strains evolved during serial passaging in the presence of BASA identified two discrete resistance mechanisms. In the first, deletion of the biotin-dependent enzyme pyruvate carboxylase is proposed to prioritize the utilization of bioavailable biotin for the essential enzyme acetyl-CoA carboxylase. In the second, a D200E missense mutation in BPL reduced DNA binding in vitro and transcriptional repression in vivo. We propose that this second resistance mechanism promotes bioavailability of biotin by derepressing its synthesis and import, such that free biotin may outcompete the inhibitor for binding BPL. This study provides new insights into the molecular mechanisms governing antibacterial activity and resistance of BPL inhibitors in S. aureus.

Phylogenomics suggests oxygen availability as a driving force in Thaumarchaeota evolution

Ammonia-oxidizing archaea (AOA) of the phylum Thaumarchaeota are widespread in marine and terrestrial habitats, playing a major role in the global nitrogen cycle. However, their evolutionary history remains unexplored, which limits our understanding of their adaptation mechanisms. Here, our comprehensive phylogenomic tree of Thaumarchaeota supports three sequential events: origin of AOA from terrestrial non-AOA ancestors, colonization of the shallow ocean, and expansion to the deep ocean. Careful molecular dating suggests that these events coincided with the Great Oxygenation Event around 2300 million years ago (Mya), and oxygenation of the shallow and deep ocean around 800 and 635-560 Mya, respectively. The first transition was likely enabled by the gain of an aerobic pathway for energy production by ammonia oxidation and biosynthetic pathways for cobalamin and biotin that act as cofactors in aerobic metabolism. The first transition was also accompanied by the loss of dissimilatory nitrate and sulfate reduction, loss of oxygen-sensitive pyruvate oxidoreductase, which reduces pyruvate to acetyl-CoA, and loss of the Wood-Ljungdahl pathway for anaerobic carbon fixation. The second transition involved gain of a K⁺ transporter and of the biosynthetic pathway for ectoine, which may function as an osmoprotectant. The third transition was accompanied by the loss of the uvr system for repairing ultraviolet light-induced DNA lesions. We conclude that oxygen availability drove the terrestrial origin of AOA and their expansion to the photic and dark oceans, and that the stressors encountered during these events were partially overcome by gene acquisitions from Euryarchaeota and Bacteria, among other sources.

Native mass spectrometry identifies an alternative DNA-binding pathway for BirA from Staphylococcus aureus

An adequate supply of biotin is vital for the survival and pathogenesis of Staphylococcus aureus. The key protein responsible for maintaining biotin homeostasis in bacteria is the biotin retention protein A (BirA, also known as biotin protein ligase). BirA is a bi-functional protein that serves both as a ligase to catalyse the biotinylation of important metabolic enzymes, as well as a transcriptional repressor that regulates biotin biosynthesis, biotin transport and fatty acid elongation. The mechanism of BirA regulated transcription has been extensively characterized in Escherichia coli, but less so in other bacteria. Biotin-induced homodimerization of E. coli BirA (EcBirA) is a necessary prerequisite for stable DNA binding and transcriptional repression. Here, we employ a combination of native mass spectrometry, in vivo gene expression assays, site-directed mutagenesis and electrophoretic mobility shift assays to elucidate the DNA binding pathway for S. aureus BirA (SaBirA). We identify a mechanism that differs from that of EcBirA, wherein SaBirA is competent to bind DNA as a monomer both in the presence and absence of biotin and/or MgATP, allowing homodimerization on the DNA. Bioinformatic analysis demonstrated the SaBirA sequence used here is highly conserved amongst other S. aureus strains, implying this DNA-binding mechanism is widely employed.

The Thaumarchaeon N. gargensis carries functional bioABD genes and has a promiscuous E. coli ΔbioH-complementing esterase EstN1

Biotin is an essential cofactor required for carboxylation and decarboxylation reactions in all domains of life. While biotin biosynthesis in most Bacteria and Eukarya is well studied, the complete pathway for this vitamer in Archaea is still not known. Detailed genome searches indicated the presence of possible bio gene clusters only in Methanococcales and Thaumarchaeota. Therefore, we analysed the functionality of the predicted genes bioA, bioB, bioD and bioF in the Thaumarchaeon Nitrososphaera gargensis Ga2.9 which are essential for the later steps of biotin synthesis. In complementation tests, the gene cluster-encoded N. gargensis bioABD genes except bioF restored growth of corresponding E. coli Rosetta-gami 2 (DE3) deletion mutants. To find out how biotin biosynthesis is initiated, we searched the genome for a possible bioH analogue encoding a pimeloyl-ACP-methylester carboxylesterase. The respective amino acid sequence of the ORF estN1 showed weak conserved domain similarity to this class of enzymes (e-value 3.70e-42). Remarkably, EstN1 is a promiscuous carboxylesterase that complements E. coli ΔbioH and Mesorhizobium loti ΔbioZ mutants for growth on biotin-free minimal medium. Additional 3D-structural models support the hypothesis that EstN1 is a BioH analogue. Thus, this is the first report providing experimental evidence that Archaea carry functional bio genes.

The Genus Macrococcus: An Insight Into Its Biology, Evolution, and Relationship With Staphylococcus

The Gram-positive genus Macrococcus is composed of eight species that are evolutionarily closely related to species of the Staphylococcus genus. In contrast to Staphylococcus species, species of Macrococcus are generally regarded to be avirulent in their animal hosts. Recent reports on Macrococcus have focused on the presence of novel methicillin resistance genes in Macrococcus caseolyticus and Macrococcus canis, with the discovery of the first plasmid-encoded methicillin resistance gene in clinical Staphylococcus aureus of probable macrococcal origin generating further interest in these organisms. Furthermore, M. caseolyticus has been associated with flavor development in certain fermented foods and its potential as a food bio-preservative has been documented. The potential application of these organisms in food seems at odds with the emerging information regarding antibiotic resistance and is prompting further examination of the potential safety issues associated with such strains, given the European Food Safety Authority framework for the safety evaluation of microorganisms in the food chain. A comprehensive understanding of the genus would also contribute to understanding the evolution of staphylococci in terms of its acquisition of antibiotic resistance and pathogenic potential. In this review, we discuss the current knowledge on Macrococcus with regard to their phenotypic capabilities, genetic diversity, and evolutionary history with Staphylococcus. Comparative genomics of the sequenced Macrococcus species will be discussed, providing insight into their unique metabolic features and the genetic structures carrying methicillin resistance. An in-depth understanding of these antibiotic resistance determinants can open the possibilities for devising better preventative strategies for an unpredictable future.

Analysis and validation of the pho regulon in the tacrolimus-producer strain Streptomyces tsukubaensis: differences with the model organism Streptomyces coelicolor

Inorganic and organic phosphate controls both primary and secondary metabolism in Streptomyces genus. Metabolism regulation by phosphate in Streptomyces species is mediated by the PhoR-PhoP two-component system. Response regulator PhoP binds to conserved sequences of 11 nucleotides called direct repeat units (DRus), whose organization and conservation determine the binding of PhoP to distinct promoters. Streptomyces tsukubaensis is the industrial producer of the clinical immunosuppressant tacrolimus (FK506). A bioinformatic genome analysis detected several genes with conserved PHO boxes involved in phosphate scavenging and transport, nitrogen regulation, and secondary metabolite production. In this article, the PhoP regulation has been confirmed by electrophoretic mobility shift assays (EMSA) of the most relevant members of the traditional pho regulon such as the two-component system PhoR-P or genes involved in high-affinity phosphate transport (pstSCAB) and low-affinity phosphate transport (pit). However, the PhoP control over phosphatase genes in S. tsukubaensis is significantly different from the pattern reported in the model bacteria Streptomyces coelicolor. Thus, neither the alkaline phosphatase PhoA nor PhoD is regulated by PhoP. On the contrary, the binding of PhoP to the promoter of a novel putative phosphatase PhoX was confirmed. A crosstalk of the PhoP and GlnR regulators, which balances phosphate and nitrogen utilization, also occurs in S. tsukubaensis but slightly modified. Finally, PhoP regulates genes, like afsS, that link phosphate control and secondary metabolite production in S. tsukubaensis. In summary, there are notable differences between the regulation of specific genes of the pho regulon in S. tsukubaensis and the model organism S. coelicolor.

Biotin-mediated growth and gene expression in Staphylococcus aureus is highly responsive to environmental biotin

Biotin (Vitamin B7) is a critical enzyme co-factor in metabolic pathways important for bacterial survival. Biotin is obtained either from the environment or by de novo synthesis, with some bacteria capable of both. In certain species, the bifunctional protein BirA plays a key role in biotin homeostasis as it regulates expression of biotin biosynthetic enzymes in response to biotin demand and supply. Here, we compare the effect of biotin on the growth of two bacteria that possess a bifunctional BirA, namely Escherichia coli and Staphylococcus aureus. Unlike E. coli that could fulfill its biotin requirements through de novo synthesis, S. aureus showed improved growth rates in media supplemented with 10 nM biotin. S. aureus also accumulated more radiolabeled biotin from the media highlighting its ability to efficiently scavenge exogenous material. These data are consistent with S. aureus colonizing low biotin microhabitats. We also demonstrate that the S. aureus BirA protein is a transcriptional repressor of BioY, a subunit of the biotin transporter, and an operon containing yhfT and yhfS, the products of which have a putative role in fatty acid homeostasis. Increased expression of bioY is proposed to help cue S. aureus for efficient scavenging in low biotin environments.

Identification and Characterization of Spontaneous Auxotrophic Mutants in Fusarium langsethiae

Analysis of 49 strains of Fusarium langsethiae originating from northern Europe (Russia, Finland, Sweden, UK, Norway, and Latvia) revealed the presence of spontaneous auxotrophic mutants that reflect natural intraspecific diversity. Our investigations detected that 49.0% of F. langsethiae strains were auxotrophic mutants for biotin, and 8.2% of the strains required thiamine as a growth factor. They failed to grow on vitamin-free media. For both prototrophic and auxotrophic strains, no growth defect was observed in rich organic media. Without essential vitamins, a significant reduction in the growth of the auxotrophic strains results in a decrease of the formation of T-2 toxin and diacetoxyscirpenol. In addition, all analysed F. langsethiae strains were distinguished into two subgroups based on PCR product sizes. According to our results, 26 and 23 strains of F. langsethiae belong to subgroups I and II respectively. We determined that the deletion in the intergenic spacer (IGS) region of the rDNA of F. langsethiae belonging to subgroup II is linked with temperature sensitivity and causes a decrease in strain growth at 30 °C. Four thiamine auxotrophic strains were found in subgroup I, while 21 biotin auxotrophic strains were detected in subgroups II. To the best of our knowledge, the spontaneous mutations in F. langsethiae observed in the present work have not been previously reported.