Restoration of active transport of solutes and oxidative phosphorylation by naphthoquinones in irradiated membrane vesicles from Mycobacterium phlei

Mechanistic insights into UV-A mediated bacterial disinfection via endogenous photosensitizers

UV-A and visible light are thought to excite endogenous photosensitizers in microbes, thereby initiating complex chemical interactions that ultimately kill cells. Natural solar-based disinfection methods have been adapted into commercial lighting technologies with varying degrees of reported efficacy and associated safety hazards for human exposure. Here we utilize a narrow-spectrum UV-A LED prototype (currently in development for health care applications) to investigate the mechanism of bacterial photoinactivation using 365 nm light. Using a combination of reverse genetics and biochemical investigation, we report mechanistic evidence that 365nm light initiates a chain-reaction of superoxide-mediated damage via auto-excitation of vitamin-based electron carriers, specifically vitamin K2 menaquinones and the FAD flavoprotein in Complex II in the electron transport chain. We observe that photoinactivation is modifiable through supplementation of the environment to bypass cell damage. Lastly, we observe that bacteria forced into metabolic dormancy by desiccation become hypersensitized to the effects of UV-A light, thereby permitting photoinactivation at fluences that are significantly lower than the industry threshold for safe human exposure. In total, these results substantiate the mechanism and potential application of narrow- spectrum UV-A light for bacterial disinfection purposes.

Biosynthesis and Regulation of Sulfomenaquinone, a Metabolite Associated with Virulence in Mycobacterium tuberculosis

Sulfomenaquinone (SMK) is a recently identified metabolite that is unique to the Mycobacterium tuberculosis (M. tuberculosis) complex and is shown to modulate its virulence. Here, we report the identification of the SMK biosynthetic operon that, in addition to a previously identified sulfotransferase stf3, includes a putative cytochrome P450 gene (cyp128) and a gene of unknown function, rv2269c. We demonstrate that cyp128 and stf3 are sufficient for the biosynthesis of SMK from menaquinone and rv2269c exhibits promoter activity in M. tuberculosis. Loss of Stf3 expression, but not that of Cyp128, is correlated with elevated levels of menaquinone-9, an essential component in the electron-transport chain in M. tuberculosis. Finally, we showed in a mouse model of infection that the loss of cyp128 exhibits a hypervirulent phenotype similar to that in previous studies of the stf3 mutant. These findings provide a platform for defining the molecular basis of SMK's role in M. tuberculosis pathogenesis.

Challenges and opportunities in developing novel drugs for TB

Mycobacterium tuberculosis is a difficult pathogen to combat and the first-line drugs currently in use are 40-60 years old. The need for new TB drugs is urgent, but the time to identify, develop and ultimately advance new drug regimens onto the market has been excruciatingly slow. On the other hand, the drugs currently in clinical development, and the recent gains in knowledge of the pathogen and the disease itself give us hope for finding new drug targets and new drug leads. In this article we highlight the unique biology of the pathogen and several possible ways to identify new TB chemical leads. The Global Alliance for TB Drug Development (TB Alliance) is a not-for-profit organization whose mission is to accelerate the discovery and development of new TB drugs. The organization carries out research and development in collaboration with many academic laboratories and pharmaceutical companies around the world. In this perspective we will focus on the early discovery phases of drug development and try to provide snapshots of both the current status and future prospects.

Active transport of Ca2+ in bacteria: bioenergetics and function

The bioenergetics of Ca2+ transport in bacteria are discussed with special emphasis on the interrelationship between transport and other cellular functions such as substrate oxidation by the respiratory chain and oxidative phosphorylation. The unusual polarity of Ca2+ movement provides an exceptional tool to compare active transport and other ATP requiring or generating processes since this ion is actively taken up by everted vesicles in which the coupling-factor ATPase is exposed to the external medium. As inferred from studies with everted vesicles, the active extrusion of Ca2+ by whole cells can be accomplished by substrate driven respiration, hydrolysis of ATP or as in the case of Streptococcus faecalis by a nonhydrolytic unknown process which involves ATP directly. Substrate oxidation and the hydrolysis of ATP result in the generation of a pH gradient which can energize the Ca2+ uptake directly (Ca2+/H+ antiport) or via a secondary Na+ gradient (Ca2+/Na+ antiport). In contrast to exponentially growing cells sporulating Bacilli accumulate Ca2+ during the synthesis of dipicolinic acid. Studies involving Ca2+ transport provided evidence in support of the hypothesis that the Mg2+ ATPase from Escherichia coli not only provides the driving force for various cellular functions but exerts a regulatory role by controlling the permeability of the membrane to protons. The different specificity requirements of various naphthoquinone analogs in the restoration of transport or oxidative phosphorylation, after the natural menaquinone has been destroyed by irradiation, has indicated that a protonmotive force is sufficient to drive active transport. However, in addition to the driving force (protonmotive force) necessary to establish oxidative phosphorylation, a specific spatial orientation of the respiratory components, such as the naphthoquinones, is essential for the utilization of the proton gradient or membrane potential or both. Finally, evidence suggesting that intracellular Ca2+ levels might play a fundamental role in bacterial homeostasis is discussed, in particular the role of Ca2+ in the process of chemotaxis and in conferring bacteria heat stability. A vitamin K-dependent carboxylation reaction has been found in Escherichia coli which is similar to that reported in mammalian systems which results in gamma carboxylation of glutamate residues. Although all of the proteins containing gamma-carboxyglutamate described so far are involved in Ca2+ metabolism, the role of these proteins in Escherichia coli is unknown and remains to be elucidated.