bMycobacteriophages infect mycobacteria, resulting in their death. Therefore, the possibility of using them as therapeutic agents against the deadly mycobacterial disease tuberculosis (TB) is of great interest. To obtain better insight into the dynamics of mycobacterial inactivation by mycobacteriophages, this study was initiated using mycobacteriophage D29 and Mycobacterium smegmatis as the phage-host system. Here, we implemented a goal-oriented iterative cycle of experiments on one hand and mathematical modeling combined with Monte Carlo simulations on the other. This integrative approach lends valuable insight into the detailed kinetics of bacterium-phage interactions. We measured time-dependent changes in host viability during the growth of phage D29 in M. smegmatis at different multiplicities of infection (MOI). The predictions emerging out of theoretical analyses were further examined using biochemical and cell biological assays. In a phage-host interaction system where multiple rounds of infection are allowed to take place, cell counts drop more rapidly than expected if cell lysis is considered the only mechanism for cell death. The phenomenon could be explained by considering a secondary factor for cell death in addition to lysis. Further investigations reveal that phage infection leads to the increased production of superoxide radicals, which appears to be the secondary factor. Therefore, mycobacteriophage D29 can function as an effective antimycobacterial agent, the killing potential of which may be amplified through secondary mechanisms.

The immune deficiency (IMD) pathway directs host defense in arthropods upon bacterial infection. In Pancrustacea, peptidoglycan recognition proteins sense microbial moieties and initiate nuclear factor-κB-driven immune responses. Proteins that elicit the IMD pathway in non-insect arthropods remain elusive. Here, we show that an Ixodes scapularis homolog of croquemort (Crq), a CD36-like protein, promotes activation of the tick IMD pathway. Crq exhibits plasma membrane localization and binds the lipid agonist 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphoglycerol. Crq regulates the IMD and jun N-terminal kinase signaling cascades and limits the acquisition of the Lyme disease spirochete B. burgdorferi . Additionally, nymphs silenced for crq display impaired feeding and delayed molting to adulthood due to a deficiency in ecdysteroid synthesis. Collectively, we establish a distinct mechanism for arthropod immunity outside of insects and crustaceans.

Metabolism influences biochemical networks and arthropod vectors are endowed with an immune system that affects microbial acquisition, persistence and transmission to humans and other animals. Here, we aim to persuade the scientific community to expand their interests in immunometabolism beyond mammalian hosts and towards arthropod vectors. Immunometabolism investigates the interplay of metabolism and immunology. We provide a conceptual framework for investigators from diverse disciplines and indicate that relationships between microbes, mammalian hosts and their hematophagous arthropods may result in cost-effective (mutualism) or energetically expensive (parasitism) interactions. We argue that disparate resource allocations between species may partially explain why some microbes act as pathogens when infecting humans and behave as mutualistic or commensal organisms when colonizing arthropod vectors.

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Mycobacterium species such as M. smegmatis and M. tuberculosis encode at least two translesion synthesis (TLS) polymerases, DinB1 and DinB2, respectively. Although predicted to be linked to DNA repair, their role in vivo remains enigmatic. M. smegmatis mc 2 155, a strain commonly used to investigate mycobacterial genetics, has two copies of dinB2, the gene that codes for DinB2, by virtue of a 56-kb chromosomal duplication. Expression of a mycobacteriophage D29 gene (gene 50) encoding a class II ribonucleotide reductase in M. smegmatis ⌬DRKIN, a strain derived from mc 2 155 in which one copy of the duplication is lost, resulted in DNA replication defects and growth inhibition. The inhibitory effect could be linked to the deficiency of dTTP that resulted under these circumstances. The selective inhibition observed in the ⌬DRKIN strain was found to be due solely to a reduced dosage of dinB2 in this strain. Mycobacterium bovis, which is closely related to M. tuberculosis, the tuberculosis pathogen, was found to be highly susceptible to gene 50 overexpression. Incidentally, these slow-growing pathogens harbor one copy of dinB2. The results indicate that the induction of a dTTP-limiting state can lead to growth inhibition in mycobacteria, with the effect being maximum in cells deficient in DinB2. IMPORTANCEMycobacterium species, such as M. tuberculosis, the tuberculosis pathogen, are known to encode several Y family DNA polymerases, one of which is DinB2, an ortholog of the DNA repair-related protein DinP of Escherichia coli. Although this protein has been biochemically characterized previously and found to be capable of translesion synthesis in vitro, its in vivo function remains unknown. Using a novel method to induce dTTP deficiency in mycobacteria, we demonstrate that DinB2 can aid mycobacterial survival under such conditions. Apart from unraveling a specific role for the mycobacterial Y family DNA polymerase DinB2 for the first time, this study also paves the way for the development of drugs that can kill mycobacteria by inducing a dTTP-deficient state. Members of the Y family DNA polymerases are capable of translesion synthesis (TLS) that allows them to catalyze the insertion of deoxyribonucleotide triphosphates (dNTPs) opposite potentially lethal replication-blocking lesions (1). The ability of these polymerases to bypass such lesions helps the cell to survive under DNA-damaging conditions. However, survival comes at a cost. Mutations are introduced more frequently than under normal conditions, as these polymerases function in an error-prone manner (2). In Escherichia coli, DinP/DinB (DNA polymerase IV [Pol IV]) and UmuC (DNA Pol V) are the two Y family polymerases that mediate TLS (2). Mutations in the genes that encode UmuC and a related protein, UmuD, result in a UV-nonmutable (umu) phenotype. In contrast, mutation of dinB, the gene that codes for the Pol IV enzyme DinB, does not lead to an apparent phenotype, and therefore, the function of this protein remains enigmatic. The expression of the E. col...