Bacterial symbionts bring a wealth of functions to the associations they participate in, but by doing so, they endanger the genes and genomes underlying these abilities. When bacterial symbionts become obligately associated with their hosts, their genomes are thought to decay towards an organelle-like fate due to decreased homologous recombination and inefficient selection. However, numerous associations exist that counter these expectations, especially in marine environments, possibly due to ongoing horizontal gene flow. Despite extensive theoretical treatment, no empirical study thus far has connected these underlying population genetic processes with long-term evolutionary outcomes. By sampling marine chemosynthetic bacterial-bivalve endosymbioses that range from primarily vertical to strictly horizontal transmission, we tested this canonical theory. We found that transmission mode strongly predicts homologous recombination rates, and that exceedingly low recombination rates are associated with moderate genome degradation in the marine symbionts with nearly strict vertical transmission. Nonetheless, even the most degraded marine endosymbiont genomes are occasionally horizontally transmitted and are much larger than their terrestrial insect symbiont counterparts. Therefore, horizontal transmission and recombination enable efficient natural selection to maintain intermediate symbiont genome sizes and substantial functional genetic variation. Symbiotic associations between bacteria and eukaryotes are ubiquitous in nature and have contributed to the evolution of radically novel phenotypes and niches for the involved partners. New metabolic or physiological capacities that arise in these associations are typically encoded by the bacterial symbiont genomes. However, the association itself endangers the retention of bacterial genomic coding capacity. Endosymbiont genome evolution theory predicts that when bacterial symbionts become restricted to host tissues, their populations cannot remove deleterious mutations efficiently. This ultimately results in their genomes degrading to small, function-poor states, reminiscent of organellar genomes. However, many ancient marine endosymbionts do not fit this prediction, but instead retain relatively large, gene-rich genomes, indicating that the evolutionary dynamics of this process need more thorough characterization. Here we show that on-going symbiont gene flow via horizontal transmission between bivalve hosts and recombination among divergent gammaproteobacterial symbiont lineages are sufficient to maintain large and dynamic bacterial symbiont genomes. These findings indicate that many obligately associated symbiont genomes may not be as isolated from one another as previously assumed and are not on a one way path to degradation.

Multidrug-resistant (MDR) Mycobacterium tuberculosis (Mtb) poses significant challenges to global tuberculosis (TB) control efforts. Host-directed therapies (HDTs) offer a novel approach to TB treatment by enhancing immune-mediated clearance of Mtb. Prior preclinical studies found that the inhibition of heme oxygenase-1 (HO-1), an enzyme involved in heme metabolism, with tin-protoporphyrin IX (SnPP) significantly reduced mouse lung bacillary burden when co-administered with the first-line antitubercular regimen. Here, we evaluated the adjunctive HDT activity of a novel HO-1 inhibitor, stannsoporfin (SnMP), in combination with a novel MDR-TB regimen comprising a next-generation diarylquinoline, TBAJ-876 (S), pretomanid (Pa), and a new oxazolidinone, TBI-223 (O) (collectively, SPaO), in Mtb-infected BALB/c mice. After 4 weeks of treatment, SPaO + SnMP 5mg/kg reduced mean lung bacillary burden by an additional 0.69 log ₁₀ ( P = 0.01) relative to SPaO alone. As early as 2 weeks post-treatment initiation, SnMP adjunctive therapy differentially altered the expression of pro-inflammatory cytokine genes and CD38, a marker of M1 macrophages. Next, we evaluated the sterilizing potential of SnMP adjunctive therapy in a mouse model of microbiological relapse. After 6 weeks of treatment, SPaO + SnMP 10mg/kg reduced lung bacterial burdens to 0.71 ± 0.23 log ₁₀ colony-forming units (CFUs), a 0.78 log-fold greater decrease in lung CFU compared to SpaO alone ( P = 0.005). However, adjunctive SnMP did not reduce microbiological relapse rates after 5 or 6 weeks of treatment. SnMP was well tolerated and did not significantly alter gross or histological lung pathology. SnMP is a promising HDT candidate requiring further study in combination with regimens for drug-resistant TB.

Mycobacterium tuberculosis ( Mtb) is one of the leading infectious causes of death worldwide. There is no available licensed therapeutic vaccine that shortens active tuberculosis (TB) disease drug treatment and prevents relapse, despite the World Health Organization’s calls. Here, we show that an intranasal DNA vaccine containing a fusion of the stringent response rel _Mtb gene with the gene encoding the immature dendritic cell-targeting chemokine, MIP-3α/CCL20, shortens the duration of curative TB treatment in immunocompetent mice. Compared to the first-line regimen for drug-susceptible TB alone, our novel adjunctive vaccine induced greater Rel _Mtb -specific T-cell responses associated with optimal TB control in spleen, blood, lungs, mediastinal lymph nodes, and bronchoalveolar lavage (BAL) fluid. These responses were sustained, if not augmented, over time. It also triggered more effective dendritic cell recruitment, activation, and colocalization with T cells, implying enhanced crosstalk between innate and adaptive immunity. Moreover, it potentiated a 6-month TB drug-resistant regimen, rendering it effective across treatment regimens, and also showed promising results in CD4+ knockout mice, perhaps due to enhanced Rel-specific CD8+ T-cell responses. Notably, our novel fusion vaccine was also immunogenic in nonhuman primates, the gold standard animal model for TB vaccine studies, eliciting antigen-specific T-cell responses in blood and BAL fluid analogous to those observed in protected mice. Our findings have critical implications for therapeutic TB vaccine clinical development in immunocompetent and immunocompromised populations and may serve as a model for defining immunological correlates of therapeutic vaccine-induced protection. One sentence summary: A TB vaccine shortens curative drug treatment in mice by eliciting strong TB-protective immune responses and induces similar responses in macaques.

Tuberculosis necrotic granulomas contain triglyceride-rich macrophages (foam cells) with reduced antimicrobial functions. We assessed the ability of 2 compounds to reduce the triglyceride content and Mycobacterium tuberculosis (Mtb) burden in infected human monocyte-derived macrophages and in the lungs of Mtb-infected C3HeB/FeJ mice: A-922500 (DGATi), an inhibitor of diacylglycerol O-acyltransferase 1, and LY2584702 (p70S6Ki), an inhibitor of p70 S6 kinase. DGATi and p70S6Ki significantly reduced the lipid content and bacillary burden in Mtb-infected macrophages. Each inhibitor reduced the cellular triglyceride content in bronchoalveolar lavage samples of Mtb-infected mice. After 6 weeks of treatment, p70S6Ki alone reduced the lung bacterial burden in Mtb-infected mice. However, DGATi alone and DGATi or p70S6Ki in combination with isoniazid did not reduce lung bacterial burden or alter lung inflammation. These findings provide further insight into the role of foam cells in tuberculosis pathogenesis and the utility of interventions targeting these cell populations as adjunctive host-directed therapies.

The alphaproteobacterium Wolbachia pipientis infects arthropod and nematode species worldwide, making it a key target for host biological control. Wolbachia -driven host reproductive manipulations, such as cytoplasmic incompatibility (CI), are credited for catapulting these intracellular bacteria to high frequencies in host populations. Positive, perhaps mutualistic, reproductive manipulations also increase infection frequencies, but are not well understood. Here, we identify molecular and cellular mechanisms by which Wolbachia influences the molecularly distinct processes of GSC self renewal and differentiation. We demonstrate that w Mel infection rescues the fertility of flies lacking the translational regulator mei-P26 , and is sufficient to sustain infertile homozygous mei-P26 -knockdown stocks indefinitely. Cytology revealed that w Mel mitigates the impact of mei-P26 loss through restoring proper pMad, Bam, Sxl, and Orb expression. In OreR files with wild-type fertility, w Mel infection elevates lifetime egg hatch rates. Exploring these phenotypes through dual-RNAseq experiments revealed that w Mel infection rescues and offsets many gene expression changes induced by mei-P26 loss at the mRNA level. Overall, we show that w Mel infection beneficially reinforces host fertility at mRNA, protein, and phenotypic levels, and these mechanisms may promote the emergence of mutualism and the breakdown of host reproductive manipulations. Graphical Highlights: ● The wMel strain of Wolbachia restores fertility in females and males deficient for the essential translational regulator meiotic-P26 ● Mei-P26’s germline maintenance and oocyte cyst differentiation functions are genetically rescued by wMel infection ● Perturbed pMad, Sxl, Bam, and Orb protein expression are mitigated by wMel infection ● wMel infection elevates lifetime egg lay and hatch rates in OreR flies ● Ovary transcriptomes reveal wMel infection restores or offsets changes in gene expression induced by the loss of functional mei-P26 Significance Statement: Wolbachia bacterial symbionts are being harnessed as biological control agents through the use of their costly manipulations to host fertility. Here, we reveal that the w Mel strain can have a beneficial impact on fruit fly development in both mutant and wild-type flies. This phenotype is essential to the long-term use of these bacteria for host population control.

Background: Post-tuberculosis lung disease causes a significant burden of global disease. While a consensus definition of post-tuberculosis lung disease is still in development, parenchymal cavitation, bronchiectasis, and fibrosis are recognized pathologic features. The molecular mechanisms driving development of each feature are largely unknown. Methods: To facilitate the mechanistic study of tuberculosis-associated pathologic tissue remodeling and fibrosis, we adapted a mouse model of infection. Results: The morphologies of fibrosis observed in mice were similar to those observed in human tissue samples, and fibrillar collagen deposition did not resolve with antituberculosis antibiotics. Inflammatory transcriptional signatures were persistently upregulated during chronic infection and did not fully resolve after weeks of antibiotics. Inflammatory and fibrosis-associated macrophages similarly persisted during treatment. Immunofluorescence microscopy revealed persistent macrophage populations and shifts in abundance and distribution of type 2 alveolar cells at sites of fibrogenesis. Conclusions: A mouse model recapitulates key aspects of tuberculosis-assocaiated fibrosis. Transcriptional and cellular markers of inflammation persist through weeks of antibiotic treatment.