Structural studies suggest a peptidoglycan hydrolase function for the Mycobacterium tuberculosis Tat-secreted protein Rv2525c

Panax notoginseng stems and leaves affect microbial community and function in cecum of duzang pigs

Panax notoginseng is a Chinese medicine with a long history in which stems and leaves are the wastes of processing Panax notoginseng and have not been effectively utilized. The effects of diets containing Panax notoginseng stems and leaves on the cecal short-chain fatty acid (SCFA) concentration and microbiome of independent pigs were studied. Diets containing Panax notoginseng stems and leaves did not affect the concentration of SCFA in the cecal contents of Duzang pigs but affected the microbial composition and diversity. Firmicutes, Proteobacteria, and Bacteroidetes dominate in the cecal of Duzang pigs. Feeding Duzang pigs with a 10% Panax notoginseng stems and leaves diet increases the abundance of Lactobacillus, Christensenellaceae R-7 group, and Akkermansia in the cecal. We found 14 genera positively associated with acetate, and they were Lactobacillus, Ruminococcaceae UCG 005, Ruminiclostridium 6; Escherichia Shigella and Family XIII AD3011 group showed negative correlations. Solobacterium, Desulfovibrio, and Erysipelatoclostridium were positively associated with propionate. Campylobacter, Clostridium sensu stricto 11, and Angelakisella were positively associated with butyrate. In conclusion, Panax notoginseng stems and leaves could affect the cecal microbial community and functional composition of Duzang pigs. Panax notoginseng stems and leaves reduce the enrichment of lipopolysaccharide biosynthetic pathway of the cecal microbiome, which may have a positive effect on intestinal health. The higher abundance of GH25 family in Duzang pig's cecal microbiome of fed Panax notoginseng stems and leaves diet. This increase may be the reason for the microbial diversity decrease.

MtrA modulates Mycobacterium tuberculosis cell division in host microenvironments to mediate intrinsic resistance and drug tolerance

The success of Mycobacterium tuberculosis (Mtb) is largely attributed to its ability to physiologically adapt and withstand diverse localized stresses within host microenvironments. Here, we present a data-driven model (EGRIN 2.0) that captures the dynamic interplay of environmental cues and genome-encoded regulatory programs in Mtb. Analysis of EGRIN 2.0 shows how modulation of the MtrAB two-component signaling system tunes Mtb growth in response to related host microenvironmental cues. Disruption of MtrAB by tunable CRISPR interference confirms that the signaling system regulates multiple peptidoglycan hydrolases, among other targets, that are important for cell division. Further, MtrA decreases the effectiveness of antibiotics by mechanisms of both intrinsic resistance and drug tolerance. Together, the model-enabled dissection of complex MtrA regulation highlights its importance as a drug target and illustrates how EGRIN 2.0 facilitates discovery and mechanistic characterization of Mtb adaptation to specific host microenvironments within the host.

Rv0500A is a transcription factor that links Mycobacterium tuberculosis environmental response with division and impacts host colonization

For Mycobacterium tuberculosis (Mtb) to successfully infect a host, it must be able to adapt to changes in its microenvironment, including to variations in ionic signals such as pH and chloride (Cl^- ), and link these responses to its growth. Transcriptional changes are a key mechanism for Mtb environmental adaptation, and we identify here Rv0500A as a novel transcriptional regulator that links Mtb environmental response and division processes. Global transcriptional profiling revealed that Rv0500A acts as a repressor and influences the expression of genes related to division, with the magnitude of its effect modulated by pH and Cl^- . Rv0500A can directly bind the promoters of several of these target genes, and we identify key residues required for its DNA-binding ability and biological effect. Overexpression of rv0500A disrupted Mtb growth morphology, resulting in filamentation that was exacerbated by high environmental Cl^- levels and acidic pH. Finally, we show that perturbation of rv0500A leads to attenuation of the ability of Mtb to colonize its host in vivo. Our work highlights the important link between Mtb environmental response and growth characteristics, and uncovers a new transcription factor involved in this critical facet of Mtb biology.

Computational identification of significant immunogenic epitopes of the putative outer membrane proteins from Mycobacterium tuberculosis

Novel vaccines are required to effectively combat the epidemic spread of tuberculosis. Using in silico approaches, this study focuses on prediction of potential B cell and T cell binding immunogenic epitopes for 30 putative outer membrane proteins of Mtb. Among these, certain immunodominant epitopes of Rv0172, Rv0295c, Rv1006, Rv2264c, and Rv2525c were found, which are capable of binding B-cell and a maximum number of MHC alleles. The selected immunodominant epitopes were screened for their allergenic and antigenic properties, their percentage identity against the human proteome and their structural properties. Further, the binding efficacy of the immunodominant epitopes of Rv0295c and Rv1006 with HLA-DRB1*04:01 was analyzed using molecular docking and molecular dynamics studies. Hence, the in silico-derived immunogenic peptides (epitopes) could potentially be used for the design of subunit vaccines against tuberculosis.

The hydrolase LpqI primes mycobacterial peptidoglycan recycling

Growth and division by most bacteria requires remodelling and cleavage of their cell wall. A byproduct of this process is the generation of free peptidoglycan (PG) fragments known as muropeptides, which are recycled in many model organisms. Bacteria and hosts can harness the unique nature of muropeptides as a signal for cell wall damage and infection, respectively. Despite this critical role for muropeptides, it has long been thought that pathogenic mycobacteria such as Mycobacterium tuberculosis do not recycle their PG. Herein we show that M. tuberculosis and Mycobacterium bovis BCG are able to recycle components of their PG. We demonstrate that the core mycobacterial gene lpqI, encodes an authentic NagZ β-N-acetylglucosaminidase and that it is essential for PG-derived amino sugar recycling via an unusual pathway. Together these data provide a critical first step in understanding how mycobacteria recycle their peptidoglycan.

Bacterial growth and division require remodelling of the cell wall, which generates free peptidoglycan fragments. Here, Moynihan et al. show that Mycobacterium tuberculosis can recycle components of their peptidoglycan, and characterise a crucial enzyme required for this process.