The mycobacterial desaturase DesA2 is associated with mycolic acid biosynthesis

Acinetobacter baumannii Employs a Rare Fatty Acid Desaturase for Niche-Specific Host Adaptation

Acinetobacter baumannii is a hospital-associated pathogen with unique fatty acid homeostasis features. This includes a reliance on desaturases for proliferation, due to an inability to generate unsaturated fatty acids during the synthesis cycles. However, there are various unexplained gaps in A. baumannii fatty acid homeostasis, such as the desaturation of de novo synthesized fatty acids. We identified a conserved desaturase (DesC) with a rare structural feature that may have roles in coordinating fatty acids with acyl carrier protein conjugants. We showed that DesC can generate fatty acids with cis double bonds in the delta-9 position. Profiling of A. baumannii fatty acids and mRNA transcripts emphasized its significance during fatty acid synthesis. DesC was found to be most critical in mouse niches where A. baumannii relies on fatty acid synthesis. This work has contributed to our understanding of core metabolic features that are key to the disease potential of A. baumannii.

Antrihabitans spumae sp. nov., a novel bacterium isolated from stable foams formed in wastewater treatment plants and emended description of the genus Antrihabitans

Three strains, designated as J27, J71T and J72, belonging to the genus Antrihabitans, were isolated from stable foams formed in activated sludge wastewater treatment plants (WWTPs) in New South Wales, Australia. Phenotypic and genomic analyses revealed that these strains belong to the Nocardiaceae family and are closely related to Antrihabitans stalagmiti. However, distinct genomic and physiological characteristics, including overall genomic relatedness indices, phylogenomic analysis, genomic metabolic profiles and MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry), confirmed their status as a new species.Ecologically, these strains showed a wide metabolic versatility, like enhanced membrane transport systems for amino acids, metals and phosphate, as well as the ability to synthesize mycolic acids, contributing to their hydrophobic nature and involvement in foam stabilization. Their adaptations likely provide a competitive advantage in WWTPs, where they persist in nutrient-rich, metal-laden and foam-stabilizing environments. The species did not present the typical rod-coccus cycle, described previously as a defining characteristic of the Antrihabitans genus. Based on their unique genomic, phenotypic and ecological features, we propose the name Antrihabitans spumae sp. nov., with strain J71T (JCM 34493T, NCIMB 15450T) designated as the type strain. Additional strains include J27 (JCM 33914, NCIMB 15449) and J72 (NCIMB 15448).

Dissecting the Ca2+ dependence of DesA1 function in Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tb) has a complex cell wall, composed largely of mycolic acids, that are crucial to its structural maintenance. The M. tb desaturase A1 (DesA1) is an essential Ca2+-binding protein that catalyses a key step in mycolic acid biosynthesis. To investigate the structural and functional significance of Ca2+ binding, we introduced mutations at key residues in its Ca2+-binding βγ-crystallin motif to generate DesA1F303A, E304Q, and F303A-E304Q. Complementation of a conditional ΔdesA1 strain of Mycobacterium smegmatis, with the Ca2+ non-binders F303A or F303A-E304Q, failed to rescue its growth phenotype; these complements also exhibited enhanced cell wall permeability. Our findings highlight the criticality of Ca2+ in DesA1 function, and its implicit role in the maintenance of mycobacterial cellular integrity.

Transcriptomic responses to antibiotic exposure in Mycobacterium tuberculosis

Transcriptional responses in bacteria following antibiotic exposure offer insights into antibiotic mechanism of action, bacterial responses, and characterization of antimicrobial resistance. We aimed to define the transcriptional antibiotic response (TAR) in Mycobacterium tuberculosis (Mtb) isolates for clinically relevant drugs by pooling and analyzing Mtb microarray and RNA-seq data sets. We generated 99 antibiotic transcription profiles across 17 antibiotics, with 76% of profiles generated using 3-24 hours of antibiotic exposure and 49% within one doubling of the WHO antibiotic critical concentration. TAR genes were time-dependent, and largely specific to the antibiotic mechanism of action. TAR signatures performed well at predicting antibiotic exposure, with the area under the receiver operating curve (AUC) ranging from 0.84-1.00 (TAR <6 hours of antibiotic exposure) and 0.76-1.00 (>6 hours of antibiotic exposure) for upregulated genes and 0.57-0.90 and 0.87-1.00, respectfully, for downregulated genes. This work desmonstrates that transcriptomics allows for the assessment of antibiotic activity in Mtb within 6 hours of exposure.

Advances in cellular and tissue-based imaging techniques for sarcoid granulomas

Sarcoidosis embodies a complex inflammatory disorder spanning multiple systems, with its origin remaining elusive. It manifests as the infiltration of inflammatory cells that coalesce into distinctive noncaseous granulomas within afflicted organs. Unraveling this disease necessitates the utilization of cellular or tissue-based imaging methods to both visualize and characterize the biochemistry of these sarcoid granulomas. Although hematoxylin and eosin stain, standard in routine use alongside cytological stains have found utility in diagnosis within clinical contexts, special stains such as Masson's trichrome, reticulin, methenamine silver, and Ziehl-Neelsen provide additional varied perspectives of sarcoid granuloma imaging. Immunohistochemistry aids in pinpointing specific proteins and gene expressions further characterizing these granulomas. Finally, recent advances in spatial transcriptomics promise to divulge profound insights into their spatial orientation and three-dimensional (3-D) molecular mapping. This review focuses on a range of preexisting imaging methods employed for visualizing sarcoid granulomas at the cellular level while also exploring the potential of the latest cutting-edge approaches like spatial transcriptomics and matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI), with the overarching goal of shedding light on the trajectory of sarcoidosis research.

Targeting polyketide synthase 13 for the treatment of tuberculosis

Tuberculosis (TB) is one of the most threatening diseases for humans, however, the drug treatment strategy for TB has been stagnant and inadequate, which could not meet current treatment needs. TB is caused by Mycobacterial tuberculosis, which has a unique cell wall that plays a crucial role in its growth, virulence, and drug resistance. Polyketide synthase 13 (Pks13) is an essential enzyme that catalyzes the biosynthesis of the cell wall and its critical role is only found in Mycobacteria. Therefore, Pks13 is a promising target for developing novel anti-TB drugs. In this review, we first introduced the mechanism of targeting Pks13 for TB treatment. Subsequently, we focused on summarizing the recent advance of Pks13 inhibitors, including the challenges encountered during their discovery and the rational design strategies employed to overcome these obstacles, which could be helpful for the development of novel Pks13 inhibitors in the future.

Mycobacterium abscessus DosRS two-component system controls a species-specific regulon required for adaptation to hypoxia

Mycobacterium abscessus (Mab), an emerging opportunistic pathogen, predominantly infects individuals with underlying pulmonary diseases such as cystic fibrosis (CF). Current treatment outcomes for Mab infections are poor due to Mab's inherent antibiotic resistance and unique host interactions that promote phenotypic tolerance and hinder drug access. The hypoxic, mucus-laden airways in the CF lung and antimicrobial phagosome within macrophages represent hostile niches Mab must overcome via alterations in gene expression for survival. Regulatory mechanisms important for the adaptation and long-term persistence of Mab within the host are poorly understood, warranting further genetic and transcriptomics study of this emerging pathogen. DosRS Mab , a two-component signaling system (TCS), is one proposed mechanism utilized to subvert host defenses and counteract environmental stress such as hypoxia. The homologous TCS of Mycobacterium tuberculosis (Mtb), DosRS Mtb , is known to induce a ~50 gene regulon in response to hypoxia, carbon monoxide (CO) and nitric oxide (NO) in vitro and in vivo. Previously, a small DosR Mab regulon was predicted using bioinformatics based on DosR Mtb motifs however, the role and regulon of DosRS Mab in Mab pathogenesis have yet to be characterized in depth. To address this knowledge gap, our lab generated a Mab dosRS knockout strain (MabΔdosRS) to investigate differential gene expression, and phenotype in an in vitro hypoxia model of dormancy. qRT-PCR and lux reporter assays demonstrate Mab_dosR and 6 predicted downstream genes are induced in hypoxia. In addition, RNAseq revealed induction of a much larger hypoxia response comprised of >1000 genes, including 127 differentially expressed genes in a dosRS mutant strain. Deletion of DosRS Mab led to attenuated growth under low oxygen conditions, a shift in morphotype from smooth to rough, and down-regulation of 216 genes. This study provides the first look at the global transcriptomic response of Mab to low oxygen conditions encountered in the airways of CF patients and within macrophage phagosomes. Our data also demonstrate the importance of DosRS Mab for adaptation of Mab to hypoxia, highlighting a distinct regulon (compared to Mtb) that is significantly larger than previously described, including both genes conserved across mycobacteria as well as Mab-specific genes.

Mycobacterium tuberculosis protease Rv3090 is associated with late cell apoptosis and participates in organ injuries and mycobacterial dissemination in mice

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb). Mtb can overcome macrophage intracellular killing and lead to persistent infections. The proteases of Mtb are critical virulence factors that participate in immune responses. We determined that Rv3090 is a cell wall-associated protease and a potential pathogenic factor. To characterize the role of Rv3090 in Mtb, recombinant Msg_Rv3090 and Msg_pAIN strains were constructed to infect macrophages and mice. Lactate dehydrogenase assays and flow cytometry results showed that Rv3090 induces late macrophage apoptosis. In vivo infection experiments indicated that Rv3090 could induce hepatocyte and lung cell apoptosis and cause pathological damage to the spleen, livers and lungs. Msg_Rv3090 specifically stimulated the secretion of inflammatory cytokines including TNF-α, IL-6 and IL-1β. Overexpression of Rv3090 significantly promoted the survival of Msg in livers and lungs. Thus, Rv3090 protease triggered late cell apoptosis and contributed to the pathogenicity and dissemination of Mtb.