Expansion of the Spore Surface Polysaccharide Layer in Bacillus subtilis by Deletion of Genes Encoding Glycosyltransferases and Glucose Modification Enzymes

Role of glycogen metabolism in Clostridioides difficile virulence

Glycogen plays a vital role as an energy reserve in various bacterial and fungal species. Clostridioides difficile possesses a glycogen metabolism operon that contains genes for both glycogen synthesis and utilization. In our investigation, we focused on understanding the significance of glycogen metabolism in the physiology and pathogenesis of C. difficile. To explore this, we engineered a C. difficile JIR8094 strain lacking glycogen synthesis capability by introducing a group II intron into the glgC gene, the operon's first component. Quantification of intracellular glycogen levels validated the impact of this modification. Interestingly, the mutant strain exhibited a 1.5-fold increase in toxin production compared with the parental strain, without significant changes in the sporulation rate. Our analysis also revealed that wild-type C. difficile spores contained glycogen, whereas spores from the mutant strain lacking stored glycogen showed increased sensitivity to physical and chemical treatments and had a shorter storage life. By suppressing glgP expression, the gene coding for glycogen-phosphorylase, via CRISPRi, we demonstrated that glycogen accumulation but not the utilization is needed for spore resilience in C. difficile. Transmission electron microscopy analysis revealed a significantly lower core/cortex ratio in glgC mutant strain spores. In hamster challenge experiments, both the parental and glgC mutant strains colonized hosts similarly; however, the mutant strain failed to induce infection relapse after antibiotic treatment cessation. These findings highlight the importance of glycogen metabolism in C. difficile spore resilience and suggest its role in disease relapse.IMPORTANCEThis study on the role of glycogen metabolism in Clostridioides difficile highlights its critical involvement in the pathogen's energy management, its pathogenicity, and its resilience. Our results also revealed that glycogen presence in spores is pivotal for their structural integrity and resistance to adverse conditions, which is essential for their longevity and infectivity. Importantly, the inability of the mutant strain to cause infection relapse in hamsters post-antibiotic treatment pinpoints a potential target for therapeutic interventions, highlighting the importance of glycogen in disease dynamics. This research thus significantly advances our understanding of C. difficile physiology and pathogenesis, offering new avenues for combating its persistence and recurrence.

Regulation of late-acting operons by three transcription factors and a CRISPR-Cas component during Myxococcus xanthus development

Upon starvation, rod-shaped Myxococcus xanthus bacteria form mounds and then differentiate into round, stress-resistant spores. Little is known about the regulation of late-acting operons important for spore formation. C-signaling has been proposed to activate FruA, which binds DNA cooperatively with MrpC to stimulate transcription of developmental genes. We report that this model can explain regulation of the fadIJ operon involved in spore metabolism, but not that of the spore coat biogenesis operons exoA-I, exoL-P, and nfsA-H. Rather, a mutation in fruA increased the transcript levels from these operons early in development, suggesting negative regulation by FruA, and a mutation in mrpC affected transcript levels from each operon differently. FruA bound to all four promoter regions in vitro, but strikingly each promoter region was unique in terms of whether or not MrpC and/or the DNA-binding domain of Nla6 bound, and in terms of cooperative binding. Furthermore, the DevI component of a CRISPR-Cas system is a negative regulator of all four operons, based on transcript measurements. Our results demonstrate complex regulation of sporulation genes by three transcription factors and a CRISPR-Cas component, which we propose produces spores suited to withstand starvation and environmental insults.

Identification of CgeA as a glycoprotein that anchors polysaccharides to the spore surface in Bacillus subtilis

The Bacillus subtilis spore is composed of a core, containing chromosomal DNA, surrounded by a cortex layer made of peptidoglycan, and a coat composed of concentric proteinaceous layers. A polysaccharide layer is added to the spore surface, and likely anchored to the crust, the coat outermost layer. However, the identity of the coat protein(s) to which the spore polysaccharides (SPS) are attached is uncertain. First, we showed that the crust proteins CotVWXYZ and CgeA were all contained in the peeled SPS layer obtained from a strain missing CotE, the outer coat morphogenetic protein, suggesting that the SPS is indeed bound to at least one of the spore surface proteins. Second, CgeA is known to be located at the most downstream position in the crust assembly pathway. An analysis of truncated variants of CgeA suggested that its N-terminal half is required for localization to the spore surface, while its C-terminal half is necessary for SPS addition. Third, an amino acid substitution strategy revealed that SPS was anchored at threonine 112 (T112), which constitutes a probable O-glycosylation site on CgeA. Our results indicated that CgeA is a glycoprotein required to initiate SPS assembly and serves as an anchor protein linking the crust and SPS layers.

Sporulation conditions influence the surface and adhesion properties of Bacillus subtilis spores

Spore-forming bacteria of the Bacillus subtilis group are responsible for recurrent contamination of processing lines in the food industry which can lead to food spoilage. The persistence of B. subtilis would be due to the high resistance of spores to extreme environmental condition and their propensity to contaminate surfaces. While it is well known that sporulation conditions modulate spore resistance properties, little is known about their effect on surface and adhesion properties. Here, we studied the impact of 13 sporulation conditions on the surface and adhesion properties of B. subtilis 168 spores. We showed that Ca2+ or Mg2+ depletion, lower oxygen availability, acidic pH as well as oxidative stresses during sporulation lead to the release of more hydrophobic and adherent spores. The consequences of these sporulation conditions on crust composition in carbohydrates and proteins were also evaluated. The crust glycans of spores produced in a sporulation medium depleted in Ca2+ or Mg2+ or oxygen-limited conditions were impaired and contained lower amounts of rhamnose and legionaminic acid. In addition, we showed that lower oxygen availability or addition of hydrogen peroxide during sporulation decreases the relative amount of two crust proteins (CgeA and CotY) and the changes observed in these conditions could be due to transcriptional repression of genes involved in crust synthesis in late stationary phase. The fact that sporulation conditions affect the ease with which spores can contaminate surfaces could explain the frequent and recurrent presence of B. subtilis spores in food processing lines.

Catalytic Materials Enabled by a Programmable Assembly of Synthetic Polymers and Engineered Bacterial Spores

Natural biological materials are formed by self-assembly processes and catalyze a myriad of reactions. Here, we report a programmable molecular assembly of designed synthetic polymers with engineered bacterial spores. This self-assembly process is driven by dynamic covalent bond formation on spore surface glycan and yields macroscopic materials that are structurally stable, self-healing, and recyclable. Molecular programming of polymer species shapes the physical properties of these materials while metabolically dormant spores allow for prolonged ambient storage. Incorporation of spores with genetically encoded functionalities enables operationally simple and repeated enzymatic catalysis. Our work combines molecular and genetic engineering to offer scalable and programmable synthesis of robust materials for sustainable biocatalysis.

A model industrial workhorse: Bacillus subtilis strain 168 and its genome after a quarter of a century

The vast majority of genomic sequences are automatically annotated using various software programs. The accuracy of these annotations depends heavily on the very few manual annotation efforts that combine verified experimental data with genomic sequences from model organisms. Here, we summarize the updated functional annotation of Bacillus subtilis strain 168, a quarter century after its genome sequence was first made public. Since the last such effort 5 years ago, 1168 genetic functions have been updated, allowing the construction of a new metabolic model of this organism of environmental and industrial interest. The emphasis in this review is on new metabolic insights, the role of metals in metabolism and macromolecule biosynthesis, functions involved in biofilm formation, features controlling cell growth, and finally, protein agents that allow class discrimination, thus allowing maintenance management, and accuracy of all cell processes. New 'genomic objects' and an extensive updated literature review have been included for the sequence, now available at the International Nucleotide Sequence Database Collaboration (INSDC: AccNum AL009126.4).

Visualization and characterization of spore morphogenesis in Paenibacillus polymyxa ATCC39564

Paenibacillus polymyxa is a spore-forming Gram-positive bacterial species. Both its sporulation process and the spore properties are poorly understood. Here, we investigated sporulation in P. polymyxa ATCC39564. When cultured at 37℃ for 24 h in sporulation medium, more than 80% of the total cells in the culture were spores. Time-lapse imaging revealed that cellular morphological changes during sporulation of P. polymyxa were highly similar to those of B. subtilis. We demonstrated that genetic deletion of spo0A, sigE, sigF, sigG, or sigK, which are highly conserved transcriptional regulators in spore forming bacteria, abolished spore formation. In P. polymyxa, spo0A was required for cell growth in sporulation medium, as well as for the initiation of sporulation. The sigE and sigF mutants formed abnormal multiple asymmetric septa during the early stage of sporulation. The sigG and sigK mutants formed forespores in the sporangium, but they did not become mature. Moreover, fluorescence reporter analysis confirmed compartment-specific gene expression of spoIID and spoVFA in the mother cell and spoIIQ and sspF in the forespore. Transmission electron microscopy imaging revealed that P. polymyxa produces multilayered endospores but lacking a balloon-shaped exosporium. Our results indicate that spore morphogenesis is conserved between P. polymyxa and B. subtilis. However, P. polymyxa genomes lack many homologues encoding spore-coat proteins that are found in B. subtills, suggesting that there are differences in the spore coat composition and surface structure between P. polymyxa and B. subtilis.

Shiga Toxin-Producing Escherichia coli and Milk Fat Globules

Shiga toxin-producing Escherichia coli (STEC) are zoonotic Gram-negative bacteria. While raw milk cheese consumption is healthful, contamination with pathogens such as STEC can occur due to poor hygiene practices at the farm level. STEC infections cause mild to serious symptoms in humans. The raw milk cheese-making process concentrates certain milk macromolecules such as proteins and milk fat globules (MFGs), allowing the intrinsic beneficial and pathogenic microflora to continue to thrive. MFGs are surrounded by a biological membrane, the milk fat globule membrane (MFGM), which has a globally positive health effect, including inhibition of pathogen adhesion. In this review, we provide an update on the adhesion between STEC and raw MFGs and highlight the consequences of this interaction in terms of food safety, pathogen detection, and therapeutic development.

Manganese Stress Adaptation Mechanisms of Bacillus safensis Strain ST7 From Mine Soil

The mechanism of bacterial adaption to manganese-polluted environments was explored using 50 manganese-tolerant strains of bacteria isolated from soil of the largest manganese mine in China. Efficiency of manganese removal by the isolated strains was investigated using atomic absorption spectrophotometry. Bacillus safensis strain ST7 was the most effective manganese-oxidizing bacteria among the tested isolates, achieving up to 82% removal at a Mn(II) concentration of 2,200 mg/L. Bacteria-mediated manganese oxide precipitates and high motility were observed, and the growth of strain ST7 was inhibited while its biofilm formation was promoted by the presence of Mn(II). In addition, strain ST7 could grow in the presence of high concentrations of Al(III), Cr(VI), and Fe(III). Genome-wide analysis of the gene expression profile of strain ST7 using the RNA-seq method revealed that 2,580 genes were differently expressed under Mn(II) exposure, and there were more downregulated genes (n = 2,021) than upregulated genes (n = 559) induced by Mn stress. KAAS analysis indicated that these differently expressed genes were mainly enriched in material metabolisms, cellular processes, organism systems, and genetic and environmental information processing pathways. A total of twenty-six genes from the transcriptome of strain ST7 were involved in lignocellulosic degradation. Furthermore, after 15 genes were knocked out by homologous recombination technology, it was observed that the transporters, multicopper oxidase, and proteins involved in sporulation and flagellogenesis contributed to the removal of Mn(II) in strain ST7. In summary, B. safensis ST7 adapted to Mn exposure by changing its metabolism, upregulating cation transporters, inhibiting sporulation and flagellogenesis, and activating an alternative stress-related sigB pathway. This bacterial strain could potentially be used to restore soil polluted by multiple heavy metals and is a candidate to support the consolidated bioprocessing community.

Bacillus subtilis YngB contributes to wall teichoic acid glucosylation and glycolipid formation during anaerobic growth

UTP-glucose-1-phosphate uridylyltransferases are enzymes that produce UDP-glucose from UTP and glucose-1-phosphate. In Bacillus subtilis 168, UDP-glucose is required for the decoration of wall teichoic acid (WTA) with glucose residues and the formation of glucolipids. The B. subtilis UGPase GtaB is essential for UDP-glucose production under standard aerobic growth conditions, and gtaB mutants display severe growth and morphological defects. However, bioinformatics predictions indicate that two other UTP-glucose-1-phosphate uridylyltransferases are present in B. subtilis. Here, we investigated the function of one of them named YngB. The crystal structure of YngB revealed that the protein has the typical fold and all necessary active site features of a functional UGPase. Furthermore, UGPase activity could be demonstrated in vitro using UTP and glucose-1-phosphate as substrates. Expression of YngB from a synthetic promoter in a B. subtilis gtaB mutant resulted in the reintroduction of glucose residues on WTA and production of glycolipids, demonstrating that the enzyme can function as UGPase in vivo. When WT and mutant B. subtilis strains were grown under anaerobic conditions, YngB-dependent glycolipid production and glucose decorations on WTA could be detected, revealing that YngB is expressed from its native promoter under anaerobic condition. Based on these findings, along with the structure of the operon containing yngB and the transcription factor thought to be required for its expression, we propose that besides WTA, potentially other cell wall components might be decorated with glucose residues during oxygen-limited growth condition.

Spore-adsorption: Mechanism and applications of a non-recombinant display system

Surface display systems have been developed to express target molecules on almost all types of biological entities from viruses to mammalian cells and on a variety of synthetic particles. Various approaches have been developed to achieve the display of many different target molecules, aiming at several technological and biomedical applications. Screening of libraries, delivery of drugs or antigens, bio-catalysis, sensing of pollutants and bioremediation are commonly considered as fields of potential application for surface display systems. In this review, the non-recombinant approach to display antigens and enzymes on the surface of bacterial spores is discussed. Examples of molecules displayed on the spore surface and their potential applications are summarized and a mechanism of display is proposed.

Extreme C-terminal element of SprA serine integrase is a potential component of the "molecular toggle switch" which controls the recombination and its directionality

In Bacillus subtilis, a sporulation-related gene, spsM, is disrupted by SPβ prophage, but reconstituted during sporulation through SPβ excision. The spsM reconstitution is catalyzed by a site-specific DNA recombinase, SprA, and its cognate recombination directionality factor, SprB. SprB interacts with SprA, directing the SprA-mediated recombination reaction from integration to excision; however, the details of the directionality control remains unclear. Here, we demonstrate the importance of the extreme C-terminal region (ECT) of SprA in the DNA recombination and directionality control. We created a series of SprA C-terminal deletants and examined their DNA-binding and recombination activities. Deletions in the ECT caused a loss of integration and excision activity, the magnitudes of which positively correlated with the deletion size. Gel shift study revealed that the loss of the integration activity was attributable to the failure of synaptic complex formation. The excision deficiency was caused by defective interaction with SprB. Moreover, alanine scanning analysis revealed that Phe532 is essential to interact with SprB. SprA_F532A , therefore, showed almost no excision activity, while retaining the integration activity. Collectively, these results suggest that the ECT plays the crucial roles in the interaction of SprA with SprB and possibly in the directional control of the recombination.

The sps Genes Encode an Original Legionaminic Acid Pathway Required for Crust Assembly in Bacillus subtilis

The crust is the outermost spore layer of most Bacillus strains devoid of an exosporium. This outermost layer, composed of both proteins and carbohydrates, plays a major role in the adhesion and spreading of spores into the environment. Recent studies have identified several crust proteins and have provided insights about their organization at the spore surface. However, although carbohydrates are known to participate in adhesion, little is known about their composition, structure, and localization. In this study, we showed that the spore surface of Bacillus subtilis is covered with legionaminic acid (Leg), a nine-carbon backbone nonulosonic acid known to decorate the flagellin of the human pathogens Helicobacter pylori and Campylobacter jejuni We demonstrated that the spsC, spsD, spsE, spsG, and spsM genes of Bacillus subtilis are required for Leg biosynthesis during sporulation, while the spsF gene is required for Leg transfer from the mother cell to the surface of the forespore. We also characterized the activity of SpsM and highlighted an original Leg biosynthesis pathway in B. subtilis Finally, we demonstrated that Leg is required for the assembly of the crust around the spores, and we showed that in the absence of Leg, spores were more adherent to stainless steel probably because of their reduced hydrophilicity and charge.IMPORTANCE Bacillus species are a major economic and food safety concern of the food industry because of their food spoilage-causing capability and persistence. Their persistence is mainly due to their ability to form highly resistant spores adhering to the surfaces of industrial equipment. Spores of the Bacillus subtilis group are surrounded by the crust, a superficial layer which plays a key role in their adhesion properties. However, knowledge of the composition and structure of this layer remains incomplete. Here, for the first time, we identified a nonulosonic acid (Leg) at the surfaces of bacterial spores (B. subtilis). We uncovered a novel Leg biosynthesis pathway, and we demonstrated that Leg is required for proper crust assembly. This work contributes to the description of the structure and composition of Bacillus spores which has been under way for decades, and it provides keys to understanding the importance of carbohydrates in Bacillus adhesion and persistence in the food industry.

Applications of Bacillus subtilis Spores in Biotechnology and Advanced Materials

The bacterium Bacillus subtilis has long been an important subject for basic studies. However, this organism has also had industrial applications due to its easy genetic manipulation, favorable culturing characteristics for large-scale fermentation, superior capacity for protein secretion, and generally recognized as safe (GRAS) status. In addition, as the metabolically dormant form of B. subtilis, its spores have attracted great interest due to their extreme resistance to many environmental stresses, which makes spores a novel platform for a variety of applications. In this review, we summarize both conventional and emerging applications of B. subtilis spores, with a focus on how their unique characteristics have led to innovative applications in many areas of technology, including generation of stable and recyclable enzymes, synthetic biology, drug delivery, and material sciences. Ultimately, this review hopes to inspire the scientific community to leverage interdisciplinary approaches using spores to address global concerns about food shortages, environmental protection, and health care.