Impact of the deletion of the six mce operons in Mycobacterium smegmatis

Genetic factors affecting storage and utilization of lipids during dormancy in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) can adopt a non-growing dormant state during infection that may be critical to both active and latent tuberculosis. During dormancy, Mtb is widely tolerant toward antibiotics, a significant obstacle in current anti-tubercular drug regimens, and retains the ability to persist in its environment. We aimed to identify novel mechanisms that permit Mtb to survive dormancy in an in vitro carbon starvation model using transposon insertion sequencing and gene expression analysis. We identified a previously uncharacterized component of the lipid transport machinery, omamC, which was upregulated and required for survival during carbon starvation. We show that OmamC plays a role both in increasing fatty acid stores during growth in rich media and enhancing fatty acid utilization during starvation. Besides its involvement in lipid metabolism, OmamC levels affected the expression of the anti-anti-sigma factor rv0516c and other genes to improve Mtb survival during carbon starvation and increase its tolerance toward rifampicin, a first-line drug effective against non-growing Mtb. Importantly, we show that Mtb can be eradicated during carbon starvation, in an OmamC-dependent manner, by inhibiting lipid metabolism with the lipase inhibitor tetrahydrolipstatin. This work casts new light into the survival processes of non-replicating, drug-tolerant Mtb by identifying new proteins involved in lipid metabolism required for the survival of dormant bacteria and exposing a potential vulnerability that could be exploited for antibiotic discovery.IMPORTANCETuberculosis is a global threat, with ~10 million yearly active cases. Many more people, however, live with "latent" infection, where Mycobacterium tuberculosis survives in a non-replicative form. When latent bacteria activate and regrow, they elicit immune responses and result in significant host damage. Replicating and non-growing bacilli can co-exist; however, non-growing bacteria are considerably less sensitive to antibiotics, thus complicating treatment by necessitating long treatment durations. Here, we sought to identify genes important for bacterial survival in this non-growing state using a carbon starvation model. We found that a previously uncharacterized gene, omamC, is involved in storing and utilizing fatty acids as bacteria transition between these two states. Importantly, inhibiting lipid metabolism using a lipase inhibitor eradicates non-growing bacteria. Thus, targeting lipid metabolism may be a viable strategy for treating the non-growing population in strategies to shorten treatment durations of tuberculosis.

Effect of Host Cholesterol on the Membrane Dynamics of Outer Membrane Lipids of Mycobacteria

The ability of Mycobacterium tuberculosis to remain dormant after primary infection represents the prime cause of new TB cases throughout the world. Hence, diagnosis and treatment of individuals hosting dormant mycobacterium is one of the crucial strategies to be adopted for the prevention of Tuberculosis. Among many strategies unleashed by the latent bacterium, one of them is scavenging host cholesterol for carbon source. Cholesterol modifies lipid membranes over many scales and here, its effect on mycobacterial membrane biophysics and the subsequent effect on partitioning of antibiotics into cholesterol- enriched mycobacterial membranes was investigated. Our research showed that cholesterol alters the phase state behavior of mycobacterial outer membrane lipids by enhancing the overall membrane order at the headgroup and acyl chain region and is integrated into both ordered and disordered domains/phases, with a preference for the latter. Exogenous cholesterol further alters the drug partitioning behavior of structurally different drugs, pointing to a larger clinical potential of using more hydrophobic medications to target dormant bacteria.

Immuno-reactivity evaluation of Mce-truncated subunit candidate vaccine against Mycobacterium avium subspecies paratuberculosis challenge in the goat models

BACKGROUND

Detection of an appropriate antigen with high immunogenicity can be a big step in the production of an effective vaccine for control of Johne's disease (JD). The aim of this study was to evaluate the efficacy of Mce-truncated protein as a subunit vaccine candidate for the control of JD in experimentally challenged goats.

MATERIALS AND METHODS

Six healthy goat kids were immunized with Mce-truncated protein, and two goats were kept as controls. All kids were twice challenged orally with live Mycobacterium avium subspecies paratuberculosis(MAP) strain and half the goats from both the categories were sacrificed at 7 and 10 months after start of challenge study. Culture of MAP was performed from all the necropsied tissues to determine the true JD infection status.

RESULTS

Mce-truncated protein only reacted with pooled vaccinated goat sera in western-blot. A significant increase in humoral immune response against Mce protein was also observed in vaccinated goats. Compared to the control group, vaccinated goats gained higher body weights and none of them shed MAP or showed histopatological lesions or colonization of MAP in their necropsy tissues.

CONCLUSIONS

The new Mce protein based vaccine provided significant immunity in goats as they could meet the challenge with live MAP bacilli. Although the vaccine used in this study showed the high potential as a new effective vaccine for the control of JD, further validation study is still required to successfully implement the vaccine for JD control program.

Structure of an endogenous mycobacterial MCE lipid transporter

To replicate inside macrophages and cause tuberculosis, Mycobacterium tuberculosis must scavenge a variety of nutrients from the host1,2. The mammalian cell entry (MCE) proteins are important virulence factors in M. tuberculosis1,3, where they are encoded by large gene clusters and have been implicated in the transport of fatty acids4-7 and cholesterol1,4,8 across the impermeable mycobacterial cell envelope. Very little is known about how cargos are transported across this barrier, and it remains unclear how the approximately ten proteins encoded by a mycobacterial mce gene cluster assemble to transport cargo across the cell envelope. Here we report the cryo-electron microscopy (cryo-EM) structure of the endogenous Mce1 lipid-import machine of Mycobacterium smegmatis-a non-pathogenic relative of M. tuberculosis. The structure reveals how the proteins of the Mce1 system assemble to form an elongated ABC transporter complex that is long enough to span the cell envelope. The Mce1 complex is dominated by a curved, needle-like domain that appears to be unrelated to previously described protein structures, and creates a protected hydrophobic pathway for lipid transport across the periplasm. Our structural data revealed the presence of a subunit of the Mce1 complex, which we identified using a combination of cryo-EM and AlphaFold2, and name LucB. Our data lead to a structural model for Mce1-mediated lipid import across the mycobacterial cell envelope.

Structure of an endogenous mycobacterial MCE lipid transporter

To replicate inside human macrophages and cause the disease tuberculosis, Mycobacterium tuberculosis ( Mtb ) must scavenge a variety of nutrients from the host 1,2 . The Mammalian Cell Entry (MCE) proteins are important virulence factors in Mtb 1,3 , where they are encoded in large gene clusters and have been implicated in the transport of fatty acids 4â€"7 and cholesterol 1,4,8 across the impermeable mycobacterial cell envelope. Very little is known about how cargos are transported across this barrier, and how the ~10 proteins encoded in a mycobacterial mce gene cluster might assemble to transport cargo across the cell envelope remains unknown. Here we report the cryo-EM structure of the endogenous Mce1 fatty acid import machine from Mycobacterium smegmatis , a non-pathogenic relative of Mtb . The structure reveals how the proteins of the Mce1 system assemble to form an elongated ABC transporter complex, long enough to span the cell envelope. The Mce1 complex is dominated by a curved, needle-like domain that appears to be unrelated to previously described protein structures, and creates a protected hydrophobic pathway for lipid transport across the periplasm. Unexpectedly, our structural data revealed the presence of a previously unknown subunit of the Mce1 complex, which we identified using a combination of cryo-EM and AlphaFold2, and name LucB. Our data lead to a structural model for Mce1-mediated fatty acid import across the mycobacterial cell envelope.

Rational development of mycobacteria cell factory for advancing the steroid biomanufacturing

Steroidal resource occupies a vital proportion in the pharmaceutical industry attributing to their important therapeutic effects on fertility, anti-inflammatory and antiviral activities. Currently, microbial transformation from phytosterol has become the dominant strategy of steroidal drug intermediate synthesis that bypasses the traditional chemical route. Mycobacterium sp. serve as the main industrial microbial strains that are capable of introducing selective functional modifications of steroidal intermediate, which has become an indispensable platform for steroid biomanufacturing. By reviewing the progress in past two decades, the present paper concentrates mainly on the microbial rational modification aspects that include metabolic pathway editing, key enzymes engineering, material transport pathway reinforcement, toxic metabolic intermediates removal and byproduct reconciliation. In addition, progress on omics analysis and direct genetic manipulation are summarized and classified that may help reform the industrial hosts with more efficiency. The paper provides an insightful present for steroid biomanufacturing especially on the current trends and prospects of mycobacteria.

Role of Ring6 in the function of the E. coli MCE protein LetB

LetB is a tunnel-forming protein found in the cell envelope of some double-membraned bacteria, and is thought to be important for the transport of lipids between the inner and outer membranes. In Escherichia coli the LetB tunnel is formed from a stack of seven rings (Ring1 - Ring7), in which each ring is composed of a homo-hexameric assembly of MCE domains. The primary sequence of each MCE domain of the LetB protein is substantially divergent from the others, making each MCE ring unique in nature. The role of each MCE domain and how it contributes to the function of LetB is not well understood. Here we probed the importance of each MCE ring for the function of LetB, using a combination of bacterial growth assays and cryo-EM. Surprisingly, we find that ΔRing3 and ΔRing6 mutants, in which Ring3 and Ring6 have been deleted, confer increased resistance to membrane perturbing agents. Specific mutations in the pore-lining loops of Ring6 similarly confer increased resistance. A cryo-EM structure of the ΔRing6 mutant shows that despite the absence of Ring6, which leads to a shorter assembly, the overall architecture is maintained, highlighting the modular nature of MCE proteins. Previous work has shown that Ring6 is dynamic and in its closed state, may restrict the passage of substrate through the tunnel. Our work suggests that removal of Ring6 may relieve this restriction. The deletion of Ring6 combined with mutations in the pore-lining loops leads to a model for the tunnel gating mechanism of LetB. Together, these results provide insight into the functional roles of individual MCE domains and pore-lining loops in the LetB protein.

Mycobacterial MCE proteins as transporters that control lipid homeostasis of the cell wall

Mammalian cell entry (mce) genes are not only present in genomes of pathogenic mycobacteria, including Mycobacterium tuberculosis (the causative agent of tuberculosis), but also in saprophytic and opportunistic mycobacterial species. MCE are conserved cell-wall proteins encoded by mce operons, which maintain an identical structure in all mycobacteria: two yrbE genes (A and B) followed by six mce genes (A, B, C, D, E and F). Although these proteins are known to participate in the virulence of pathogenic mycobacteria, the presence of the operons in nonpathogenic mycobacteria and other bacteria indicates that they play another role apart from host cell invasion. In this respect, more recent studies suggest that they are functionally similar to ABC transporters and form part of lipid transporters in Actinobacteria. To date, most reviews on mce operons in the literature discuss their role in virulence. However, according to data from transcriptional studies, mce genes, particularly the mce1 and mce4 operons, modify their expression according to the carbon source and upon hypoxia, starvation, surface stress and oxidative stress; which suggests a role of MCE proteins in the response of Mycobacteria to external stressors. In addition to these data, this review also summarizes the studies demonstrating the role of MCE proteins as lipid transporters as well as the relevance of their transport function in the interaction of pathogenic Mycobacteria with the hosts. Altogether, the evidence to date would indicate that MCE proteins participate in the response to the stress conditions that mycobacteria encounter during infection, by participating in the cell wall remodelling and possibly contributing to lipid homeostasis.

Mycolicibacterium cell factory for the production of steroid-based drug intermediates

Steroid-based drugs have been developed as the second largest medical category in pharmaceutics. The well-established route of steroid industry includes two steps: the conversion of natural products with a steroid framework to steroid-based drug intermediates and the synthesis of varied steroid-based drugs from steroid-based drug intermediates. The biosynthesis of steroid-based drug intermediates from phytosterols by Mycolicibacterium cell factories bypasses the potential undersupply of diosgenin in the traditional steroid chemical industry. Moreover, the biosynthesis route shows advantages on multiple steroid-based drug intermediate products, more ecofriendly processes, and consecutive reactions carried out in one operation step and in one pot. Androsta-4-ene-3,17-dione (AD), androsta-1,4-diene-3,17-dione (ADD) and 9-hydroxyandrostra-4-ene-3,17-dione (9-OH-AD) are the representative steroid-based drug intermediates synthesized by mycolicibacteria. Other steroid metabolites of mycolicibacteria, like 4-androstene-17β-ol-3-one (TS), 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC), 22-hydroxy-23,24-bisnorchol-1,4-diene-3-one (1,4-HBC), 9,22-dihydroxy-23,24-bisnorchol-4-ene-3-one (9-OH-HBC), 3aα-H-4α-(3'-propionic acid)-7aβ-methylhexahydro-1,5-indanedione (HIP) and 3aα-H-4α-(3'-propionic acid)-5α-hydroxy-7aβ-methylhexahydro-1-indanone-δ-lactone (HIL), also show values as steroid-based drug intermediates. To improve the bio-production efficiency of the steroid-based drug intermediates, mycolicibacterial strains and biotransformation processes have been continuously studied in the past decades. Many mycolicibacteria that accumulate steroid drug intermediates have been isolated, and subsequently optimized by conventional mutagenesis and genetic engineering. Especially, with the clarification of the mycolicibacterial steroid metabolic pathway and the developments on gene editing technologies, rational design is becoming an important measure for the construction and optimization of engineered mycolicibacteria strains that produce steroid-based drug intermediates. Hence, by reviewing researches in the past two decades, this article updates the overall process of steroid metabolism in mycolicibacteria and provides comprehensive schemes for the rational construction of mycolicibacterial strains that accumulate steroid-based drug intermediates. In addition, the special strategies for the bioconversion of highly hydrophobic steroid in aqueous media are discussed as well.

Evidence for the Mycobacterial Mce4 Transporter Being a Multiprotein Complex

Mycobacteria possess Mce transporters that import lipids and are thought to function analogously to ATP-binding cassette (ABC) transporters. However, whereas ABC transporters import substrates using a single solute-binding protein (SBP) to deliver a substrate to permease proteins in the membrane, mycobacterial Mce transporters have a potential for six SBPs (MceA to MceF) working with a pair of permeases (YrbEA and YrbEB), a cytoplasmic ATPase (MceG), and multiple Mce-associated membrane (Mam) and orphaned Mam (Omam) proteins to transport lipids. In this study, we used the model mycobacterium Mycobacterium smegmatis to study the requirement for individual Mce, Mam, and Omam proteins in Mce4 transport of cholesterol. All of the Mce4 and Mam4 proteins we investigated were required for cholesterol uptake. However, not all Omam proteins, which are encoded by genes outside mce loci, proved to contribute to cholesterol import. OmamA and OmamB were required for cholesterol import, while OmamC, OmamD, OmamE, and OmamF were not. In the absence of any single Mce4, Mam4, or Omam protein that we tested, the abundance of Mce4A and Mce4E declined. This relationship between the levels of Mce4A and Mce4E and these additional proteins suggests a network of interactions that assemble and/or stabilize a multiprotein Mce4 transporter complex. Further support for Mce transporters being multiprotein complexes was obtained by immunoprecipitation-mass spectrometry, in which we identified every single Mce, YrbE, MceG, Mam, and Omam protein with a role in cholesterol transport as associating with Mce4A. This study represents the first time any of these Mce4 transporter proteins has been shown to associate.IMPORTANCE How lipids travel between membranes of diderm bacteria is a challenging mechanistic question because lipids, which are hydrophobic molecules, must traverse a hydrophilic periplasm. This question is even more complex for mycobacteria, which have a unique cell envelope that is highly impermeable to molecules. A growing body of knowledge identifies Mce transporters as lipid importers for mycobacteria. Here, using protein stability experiments and immunoprecipitation-mass spectrometry, we provide evidence for mycobacterial Mce transporters existing as multiprotein complexes.

LetB Structure Reveals a Tunnel for Lipid Transport across the Bacterial Envelope

Gram-negative bacteria are surrounded by an outer membrane composed of phospholipids and lipopolysaccharide, which acts as a barrier and contributes to antibiotic resistance. The systems that mediate phospholipid trafficking across the periplasm, such as MCE (Mammalian Cell Entry) transporters, have not been well characterized. Our ~3.5 Å cryo-EM structure of the E. coli MCE protein LetB reveals an ~0.6 megadalton complex that consists of seven stacked rings, with a central hydrophobic tunnel sufficiently long to span the periplasm. Lipids bind inside the tunnel, suggesting that it functions as a pathway for lipid transport. Cryo-EM structures in the open and closed states reveal a dynamic tunnel lining, with implications for gating or substrate translocation. Our results support a model in which LetB establishes a physical link between the two membranes and creates a hydrophobic pathway for the translocation of lipids across the periplasm.

Unraveling the 17β-Estradiol Degradation Pathway in Novosphingobium tardaugens NBRC 16725

We have analyzed the catabolism of estrogens in Novosphingobium tardaugens NBRC 16725, which is able to use endocrine disruptors such as 17β-estradiol, estrone, and estriol as sole carbon and energy sources. A transcriptomic analysis enabled the identification of a cluster of catabolic genes (edc cluster) organized in two divergent operons that are involved in estrogen degradation. We have developed genetic tools for this estrogen-degrading bacterium, allowing us to delete by site-directed mutagenesis some of the genes of the edc cluster and complement them by using expression plasmids to better characterize their precise role in the estrogen catabolism. Based on these results, a catabolic pathway is proposed. The first enzyme of the pathway (17β-hydroxysteroid dehydrogenase) used to transform 17β-estradiol into estrone is encoded out of the cluster. A CYP450 encoded by the edcA gene performs the second metabolic step, i.e., the 4-hydroxylation of estrone in this strain. The edcB gene encodes a 4-hydroxyestrone-4,5-dioxygenase that opens ring A after 4-hydroxylation. The initial steps of the catabolism of estrogens and cholate proceed through different pathways. However, the degradation of estrogens converges with the degradation of testosterone in the final steps of the lower catabolic pathway used to degrade the common intermediate 3aα-H-4α(3'-propanoate)7a-β-methylhexahydro-1,5-indanedione (HIP). The TonB-dependent receptor protein EdcT appears to be involved in estrogen uptake, being the first time that this kind of proteins has been involved in steroid transport.

Biofilms of the non-tuberculous Mycobacterium chelonae form an extracellular matrix and display distinct expression patterns

Mycobacterium chelonae is an environmental, non-tuberculous mycobacterial species, capable of causing infections in humans. Biofilm formation is a key strategy used by M. chelonae in colonising niches in the environment and in the host. We studied a water-air interface (pellicle) biofilm of M. chelonae using a wide array of approaches to outline the molecular structure and composition of the biofilm. Scanning electron micrographs showed that M. chelonae biofilms produced an extracellular matrix. Using a combination of biochemical analysis, Raman spectroscopy, and fluorescence microscopy, we showed the matrix to consist of proteins, carbohydrates, lipids and eDNA. Glucose was the predominant sugar present in the biofilm matrix, and its relative abundance decreased in late (established) biofilms. RNA-seq analysis of the biofilms showed upregulation of genes involved in redox metabolism. Additionally, genes involved in mycolic acid, other lipid and glyoxylate metabolism were also upregulated in the early biofilms.

Efficient method for targeted gene disruption by homologous recombination in Mycobacterium avium subspecie paratuberculosis

Targeted gene disruption by homologous recombination, has been widely used in mycobacterium species to understand the genetic basis of virulence and persistence in the host and to develop efficacious potential live vaccines. However, in slow growing pathogenic mycobacteria as Mycobacterium avium subsp paratuberculosis (MAP), these methods have been inefficient, in part due to the low frequency of legitimate homologous recombination. Another feature of mycobacteria is the low efficiency of transformation; therefore, some years ago, a phage-mediated transduction process was developed to introduce DNA into mycobacteria. This strategy is very efficient, due to the high rate of infection of the phage. This report describes a genetic method for the generation of targeted deletion mutations in MAP by allelic exchange using in vitro-generated specialized transducing mycobacteriophages, which does not require the critical packaging step and that could also be applied to other mycobacteria. We provide a detailed gene deletion methodology and demonstrate the use of this genetic system by deleting the mce4 operon of MAP. Finally, our results showed that the deletion of mce4 in MAP induces triacylglycerol accumulation; alter morphology and aggregation in liquid culture.

Mammalian cell entry operons; novel and major subset candidates for diagnostics with special reference to Mycobacterium avium subspecies paratuberculosis infection

Mammalian cell entry (mce) genes are the components of the mce operon and play a vital role in the entry of Mycobacteria into the mammalian cell and their survival within phagocytes and epithelial cells. Mce operons are present in the DNA of Mycobacteria and translate proteins associated with the invasion and long-term existence of these pathogens in macrophages. The exact mechanism of action of mce genes and their functions are not clear yet. However, with the loss of these genes Mycobacteria lose their pathogenicity. Mycobacterium avium subspecies paratuberculosis (MAP), the etiological agent of Johne’s disease, is the cause of chronic enteritis of animals and significantly affects economic impact on the livestock industry. Since MAP is not inactivated during pasteurization, human population is continuously at the risk of getting exposed to MAP infection through consumption of dairy products. There is need for new candidate genes and/or proteins for developing improved diagnostic assays for the diagnosis of MAP infection and for the control of disease. Increasing evidences showed that expression of mce genes is important for the virulence of MAP. Whole-genome DNA microarray representing MAP revealed that there are 14 large sequence polymorphisms with LSPP12 being the most widely conserved MAP-specific region that included a cluster of six homologs of mce-family involved in lipid metabolism. On the other hand, LSP11 comprising part of mce2 operon was absent in MAP isolates. This review summarizes the advancement of research on mce genes of Mycobacteria with special reference to the MAP infection.

Mycobacterium tuberculosis Uses Mce Proteins to Interfere With Host Cell Signaling

Tuberculosis continues to be the main cause for mortality by an infectious agent, making Mycobacterium tuberculosis one of the most successful pathogens to survive for long durations within human cells. In order to survive against host defenses, M. tuberculosis modulates host cell signaling. It employs many proteins to achieve this and the Mce proteins are emerging as one group that play a role in host cell signaling in addition to their primary role as lipid/sterol transporters. Mce proteins belong to the conserved Mce/MlaD superfamily ubiquitous in diderm bacteria and chloroplasts. In mycobacteria, mce operons, encode for six different Mce proteins that assemble with inner membrane permeases into complexes that span across the mycobacterial cell wall. Their involvement in signaling modulation is varied and they have been shown to bind ERK1/2 to alter host cytokine expression; eEF1A1 to promote host cell proliferation and integrins for host cell adherence and entry. Recently, structures of prokaryotic Mce/MlaD proteins have been determined, giving an insight into the conserved domain. In this mini-review, we discuss current evidence for the role of mycobacterial Mce proteins in host cell signaling and structural characteristics of the protein-protein interactions coordinated by the human proteins to modulate the host signaling.

Intermembrane transport: Glycerophospholipid homeostasis of the Gram-negative cell envelope

This perspective addresses recent advances in lipid transport across the Gram-negative inner and outer membranes. While we include a summary of previously existing literature regarding this topic, we focus on the maintenance of lipid asymmetry (Mla) pathway. Discovered in 2009 by the Silhavy group [J. C. Malinverni, T. J. Silhavy, Proc. Natl. Acad. Sci. U.S.A. 106, 8009–8014 (2009)], Mla has become increasingly appreciated for its role in bacterial cell envelope physiology. Through the work of many, we have gained an increasingly mechanistic understanding of the function of Mla via genetic, biochemical, and structural methods. Despite this, there is a degree of controversy surrounding the directionality in which Mla transports lipids. While the initial discovery and subsequent studies have posited that it mediated retrograde lipid transport (removing glycerophospholipids from the outer membrane and returning them to the inner membrane), others have asserted the opposite. This Perspective aims to lay out the evidence in an unbiased, yet critical, manner for Mla-mediated transport in addition to postulation of mechanisms for anterograde lipid transport from the inner to outer membranes.

Steroids as Environmental Compounds Recalcitrant to Degradation: Genetic Mechanisms of Bacterial Biodegradation Pathways

Steroids are perhydro-1,2-cyclopentanophenanthrene derivatives that are almost exclusively synthesised by eukaryotic organisms. Since the start of the Anthropocene, the presence of these molecules, as well as related synthetic compounds (ethinylestradiol, dexamethasone, and others), has increased in different habitats due to farm and municipal effluents and discharge from the pharmaceutical industry. In addition, the highly hydrophobic nature of these molecules, as well as the absence of functional groups, makes them highly resistant to biodegradation. However, some environmental bacteria are able to modify or mineralise these compounds. Although steroid-metabolising bacteria have been isolated since the beginning of the 20th century, the genetics and catabolic pathways used have only been characterised in model organisms in the last few decades. Here, the metabolic alternatives used by different bacteria to metabolise steroids (e.g., cholesterol, bile acids, testosterone, and other steroid hormones), as well as the organisation and conservation of the genes involved, are reviewed.

New insights into the genome of Rhodococcus ruber strain Chol-4

Background

Rhodococcus ruber strain Chol-4, a strain isolated from a sewage sludge sample, is able to grow in minimal medium supplemented with several compounds, showing a broad catabolic capacity. We have previously determined its genome sequence but a more comprehensive study of their metabolic capacities was necessary to fully unravel its potential for biotechnological applications.

Results

In this work, the genome of R. ruber strain Chol-4 has been re-sequenced, revised, annotated and compared to other bacterial genomes in order to investigate the metabolic capabilities of this microorganism. The analysis of the data suggests that R. ruber Chol-4 contains several putative metabolic clusters of biotechnological interest, particularly those involved on steroid and aromatic compounds catabolism.

To demonstrate some of its putative metabolic abilities, R. ruber has been cultured in minimal media containing compounds belonging to several of the predicted metabolic pathways. Moreover, mutants were built to test the naphtalen and protocatechuate predicted catabolic gene clusters.

Conclusions

The genomic analysis and experimental data presented in this work confirm the metabolic potential of R. ruber strain Chol-4. This strain is an interesting model bacterium due to its biodegradation capabilities. The results obtained in this work will facilitate the application of this strain as a biotechnological tool.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5677-2) contains supplementary material, which is available to authorized users.

The extracellular matrix of mycobacterial biofilms: could we shorten the treatment of mycobacterial infections?

A number of non-tuberculous mycobacterium species are opportunistic pathogens and ubiquitously form biofilms. These infections are often recalcitrant to treatment and require therapy with multiple drugs for long duration. The biofilm resident bacteria also display phenotypic drug tolerance and thus it has been hypothesized that the drug unresponsiveness in vivo could be due to formation of biofilms inside the host. We have discussed the biofilms of several pathogenic non-tuberculous mycobacterium (NTM) species in context to the in vivo pathologies. Besides pathogenic NTMs, Mycobacterium smegmatis is often used as a model organism for understanding mycobacterial physiology and has been studied extensively for understanding the mycobacterial biofilms. A number of components of the mycobacterial cell wall such as glycopeptidolipids, short chain mycolic acids, monomeromycolyl diacylglycerol, etc. have been shown to play an important role in formation of pellicle biofilms. It shall be noted that these components impart a hydrophobic character to the mycobacterial cell surface that facilitates cell to cell interaction. However, these components are not necessarily the constituents of the extracellular matrix of mycobacterial biofilms. In the end, we have described the biofilms of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis. Three models of Mtb biofilm formation have been proposed to study the factors regulating biofilm formation, the physiology of the resident bacteria, and the nature of the biomaterial that holds these bacterial masses together. These models include pellicle biofilms formed at the liquid-air interface of cultures, leukocyte lysate-induced biofilms, and thiol reductive stressinduced biofilms. All the three models offer their own advantages in the study of Mtb biofilms. Interestingly, lipids (mainly keto-mycolic acids) are proposed to be the primary component of extracellular polymeric substance (EPS) in the pellicle biofilm, whereas the leukocyte lysate-induced and thiol reductive stress-induced biofilms possess polysaccharides as the primary component of EPS. Both models also contain extracellular DNA in the EPS. Interestingly, thiol reductive stressinduced Mtb biofilms are held together by cellulose and yet unidentified structural proteins. We believe that a better understanding of the EPS of Mtb biofilms and the physiology of the resident bacteria will facilitate the development of shorter regimen for TB treatment.

Unravelling a new catabolic pathway of C-19 steroids in Mycobacterium smegmatis

In this work, we have characterized the C-19+ gene cluster (MSMEG_2851 to MSMEG_2901) of Mycobacterium smegmatis. By in silico analysis, we have identified the genes encoding enzymes involved in the modification of the A/B steroid rings during the catabolism of C-19 steroids in certain M. smegmatis mutants mapped in the PadR-like regulator (MSMEG_2868), that constitutively express the C-19+ gene cluster. By using gene complementation assays, resting-cell biotransformations and deletion mutants, we have characterized the most critical genes of the cluster, that is, kstD2, kstD3, kshA2, kshB2, hsaA2, hsaC2 and hsaD2. These results have allowed us to propose a new catabolic route named C-19+ pathway for the mineralization of C-19 steroids in M. smegmatis. Our data suggest that the deletion of the C-19+ gene cluster may be useful to engineer more robust and efficient M. smegmatis strains to produce C-19 steroids from sterols. Moreover, the new KshA2, KshB2, KstD2 and KstD3 isoenzymes may be useful to design new microbial cell factories for the 9α-hydroxylation and/or Δ1-dehydrogenation of 3-ketosteroids.

A Novel Calcium Uptake Transporter of Uncharacterized P-Type ATPase Family Supplies Calcium for Cell Surface Integrity in Mycobacterium smegmatis

Ca²⁺ plays an important role in the physiology of bacteria. Intracellular Ca²⁺ concentrations are tightly maintained in the nanomolar range. Molecular mechanisms of Ca²⁺ uptake in bacteria remain elusive. Here we show that CtpE is responsible for Ca²⁺ uptake in Mycobacterium smegmatis. It represents a previously uncharacterized P-type ATPase family in bacteria. Disruption of ctpE in M. smegmatis resulted in a mutant with impaired growth under Ca²⁺-deficient conditions. The growth defect of the mutant could be rescued by Ca²⁺ or by ectopic expression of ctpE from M. smegmatis or the orthologous gene (Rv0908) from Mycobacterium tuberculosis H37Rv. Radioactive transport assays revealed that CtpE is a Ca²⁺-specific transporter. Ca²⁺ deficiency increased expression of ctpE, resulting in increased ⁴⁵Ca²⁺ accumulation in cells. ctpE is a gene that is part of an operon, which is negatively regulated by Ca²⁺. The ctpE mutant also showed hypersensitivity to polymyxin B, increased biofilm formation, and higher cell aggregation, indicating cell envelope defects. Our work establishes, for the first time, the presence of Ca²⁺ uptake pumps of the energy-dependent P-type ATPase superfamily in bacteria and also implicates that intracellular Ca²⁺ is essential for growth and cell envelope integrity in M. smegmatis.

Ca²⁺ is essential for gene regulation, enzymatic activity, and maintenance of structural integrity of cell walls in bacteria. Bacteria maintain intracellular calcium concentrations in a narrow range, creating a gradient with low cytoplasmic calcium concentration and high extracellular calcium concentration. Due to this steep gradient, active pumps belonging to family 2 of P-type ATPases and antiporters are used for Ca²⁺ efflux, whereas Ca²⁺ uptake is usually carried out by channels. Molecular mechanisms of Ca²⁺ uptake in bacteria are still elusive and are mainly limited to a nonproteinaceous channel in Escherichia coli and a pH-dependent channel protein from Bacillus subtilis. Energy-dependent active transporters are not reported for Ca²⁺ uptake from any organism. Here we show that CtpE belonging to a family of previously uncharacterized bacterial P-type ATPases is involved in specific uptake of Ca²⁺ into Mycobacterium smegmatis. We also demonstrate that intracellular Ca²⁺ obtained through CtpE is essential for growth and maintenance of cell surface properties under Ca²⁺-deficient conditions.

Molecular and functional analysis of the mce4 operon in Mycobacterium smegmatis

Mycobacterium smegmatis contains 6 homologous mce (mammalian cell entry) operons which have been proposed to encode ABC-like import systems. The mce operons encode up to 10 different proteins of unknown function that are not present in conventional ABC transporters. We have analysed the consequences of individually deleting each of the genes of the mce4 operon of M. smegmatis, which mediates the transport of cholesterol. None of the mce4 mutants were able to grow in cholesterol suggesting that all these genes are required for its uptake and that none of them can be replaced by the homologous genes of the other mce operons. This result suggests that different mce operons do not provide redundant capabilities and that M. smegmatis, in contrast with Mycobacterium tuberculosis, is not able to use alternative systems to import cholesterol in the analysed culture conditions. Either deletion of the entire mce4 operon or single point mutations that eliminate the transport function cause a phenotype similar to the one observed in a mutant lacking all 6 mce operons suggesting a pleiotropic role for this system.

MCE domain proteins: conserved inner membrane lipid-binding proteins required for outer membrane homeostasis

Bacterial proteins with MCE domains were first described as being important for Mammalian Cell Entry. More recent evidence suggests they are components of lipid ABC transporters. In Escherichia coli, the single-domain protein MlaD is known to be part of an inner membrane transporter that is important for maintenance of outer membrane lipid asymmetry. Here we describe two multi MCE domain-containing proteins in Escherichia coli, PqiB and YebT, the latter of which is an orthologue of MAM-7 that was previously reported to be an outer membrane protein. We show that all three MCE domain-containing proteins localise to the inner membrane. Bioinformatic analyses revealed that MCE domains are widely distributed across bacterial phyla but multi MCE domain-containing proteins evolved in Proteobacteria from single-domain proteins. Mutants defective in mlaD, pqiAB and yebST were shown to have distinct but partially overlapping phenotypes, but the primary functions of PqiB and YebT differ from MlaD. Complementing our previous findings that all three proteins bind phospholipids, results presented here indicate that multi-domain proteins evolved in Proteobacteria for specific functions in maintaining cell envelope homeostasis.

Comparative analysis of the genomes of clinical isolates of Mycobacterium avium subsp. hominissuis regarding virulence-related genes

PURPOSE

Mycobacterium avium subsp. hominissuis is a member of the M. avium complex, a heterogeneous group of bacteria that cause lung infection in immunocompetent patients or disseminated infection in patients with immunosuppression. The bacteria belonging to this complex have variable virulence, depending on the strain considered, and therefore a representative of the most common clinical phenotype was analysed.

METHODOLOGY

The genomic sequences of four M. avium subsp. hominissuis isolates obtained from clinical specimens were completed. Mav101, Mav100 and MavA5 were isolated from the blood of patients with AIDS. MavA5 was disseminated from the lung, while Mav3388 was isolated from the lungs of a patient with chronic lung disease. The sequences were annotated using the published Mav104 genome as a blueprint. Functional and virulence analyses of the sequences were carried out. Mice studies comparing the virulence of the strains were performed.

RESULTS

Findings showed that while Mav101 was very similar to Mav104, there were numerous differences between Mav104 and the remaining strains at nucleotide and predicted protein levels. The presence of genes associated with biofilm formation and several known virulence-related genes were sometimes differentially present among the isolates, suggesting overlapping functions by different genetic determinants.

CONCLUSIONS

The sequences provided important information about M. avium heterogenicity and evolution as a pathogen. The limitation is the lack of understanding on possible overlapping functions of genes/proteins.

Unravelling the pleiotropic role of the MceG ATPase in Mycobacterium smegmatis

The Mce systems are complex ABC transporters that are encoded by different numbers of homologous operons in Actinobacteria. While the four Mce systems of Mycobacterium tuberculosis are all energized by a single ATPase, MceG, each system appears to import different fatty acids or sterols. To explore if this behaviour can be extended to saprophytic mycobacteria, whose more complex genomes encode more Mce systems, we have identified and characterized the MceG orthologue of Mycobacterium smegmatis. This bacterium relies on MceG to energize its six Mce systems that contribute to a variety of cellular functions including sterol uptake and cell envelope maintenance. In the absence of MceG, M. smegmatis was not able to utilize cholesterol or phytosterols as carbon sources implying that this ATPase is necessary to energize the Mce4-sterol transport system. Other phenotypic alterations observed in the ΔMceG mutant, such as cell envelope modifications, suggest a pleiotropic functionality of the Mce systems that are particularly important for stress responses. Several ΔMceG phenotypes were recapitulated in a strain lacking only the unique C-terminal region of MceG, suggesting an important functional or regulatory function for this domain.

Architectures of Lipid Transport Systems for the Bacterial Outer Membrane

How phospholipids are trafficked between the bacterial inner and outer membranes through the hydrophilic space of the periplasm is not known. We report that members of the mammalian cell entry (MCE) protein family form hexameric assemblies with a central channel capable of mediating lipid transport. The E. coli MCE protein, MlaD, forms a ring associated with an ABC transporter complex in the inner membrane. A soluble lipid-binding protein, MlaC, ferries lipids between MlaD and an outer membrane protein complex. In contrast, EM structures of two other E. coli MCE proteins show that YebT forms an elongated tube consisting of seven stacked MCE rings, and PqiB adopts a syringe-like architecture. Both YebT and PqiB create channels of sufficient length to span the periplasmic space. This work reveals diverse architectures of highly conserved protein-based channels implicated in the transport of lipids between the membranes of bacteria and some eukaryotic organelles.

Molecular characterization of a new gene cluster for steroid degradation in Mycobacterium smegmatis

The C-19 steroids 4-androstene-3,17-dione (AD), 1,4-androstadiene-3,17-dione (ADD) or 9α-hydroxy-4-androstene-3,17-dione (9OH-AD), which have been postulated as intermediates of the cholesterol catabolic pathway in Mycobacterium smegmatis, cannot be used as sole carbon and energy sources by this bacterium. Only the ΔkstR mutant which constitutively expresses the genes repressed by the KstR regulator can metabolize AD and ADD with severe difficulties but still cannot metabolize 9OH-AD, suggesting that these compounds are not true intermediates but side products of the cholesterol pathway. However, we have found that some M. smegmatis spontaneous mutants mapped in the PadR-like regulator (MSMEG_2868) can efficiently metabolize all C-19 steroids. We have demonstrated that the PadR mutants allow the expression of a gene cluster named C-19+ (MSMEG_2851 to MSMEG_2901) encoding steroid degrading enzymes, that are not expressed under standard culture conditions. The C-19+ cluster has apparently evolved independently from the upper cholesterol kstR-regulon, but both clusters converge on the lower cholesterol kstR2-regulon responsible for the metabolism of C and D steroid rings. Homologous C-19+ clusters have been found only in other actinobacteria that metabolize steroids, but remarkably it is absent in Mycobacterium tuberculosis.

Detection of a Putative TetR-Like Gene Related to Mycobacterium bovis BCG Growth in Cholesterol Using a gfp-Transposon Mutagenesis System

In vitro transposition is a powerful genetic tool for identifying mycobacterial virulence genes and studying virulence factors in relation to the host. Transposon shuttle mutagenesis is a method for constructing stable insertions in the genome of different microorganisms including mycobacteria. Using an IS1096 derivative, we have constructed the Tngfp, a transposon containing a promoterless green fluorescent protein (gfp) gene. This transposon was able to transpose randomly in Mycobacterium bovis BCG. Bacteria with a single copy of the gfp gene per chromosome from an M. bovis BCG::Tngfp library were analyzed and cells exhibiting high levels of fluorescence were detected by flow cytometry. Application of this approach allowed for the selection of a mutant, BCG_2177c::Tngfp (BCG-Tn), on the basis of high level of long-standing fluorescence at stationary phase. This BCG-Tn mutant showed some particular phenotypic features compared to the wild type strain, mainly during stationary phase, when cholesterol was used as a sole carbon source, thus supporting the relationships of the targeted gene with the regulation of cholesterol metabolism in this bacteria. This approach showed that Tngfp is a potentially useful tool for studying the involvement of the targeted loci in metabolic pathways of mycobacteria.

The mycobacterial P55 efflux pump is required for optimal growth on cholesterol

Cholesterol catabolism is thought to be a key factor contributing to the pathogenesis of Mycobacterium tuberculosis. Previous epistasis and mutant screening studies predicted that the P55 efflux pump (Rv1410c) positively interacts with the Mce4 transporter, a major cholesterol import system of M. tuberculosis and is needed for optimal growth in vitro, in macrophages, and in vivo. Using a combination of cell growth kinetic techniques, cholesterol consumption, and [4-(14)C]cholesterol uptake studies, we demonstrated that the Mycobacterium bovis BCG rv1410c gene indeed is needed for optimal in vitro growth on cholesterol and other carbon sources. Our data, together with previous predictions, support hypotheses that the P55 efflux pump functions in maintaining general metabolism or as a subunit of the Mce4 transport apparatus (catalyzing its assembly or providing cell wall integrity) to allow more efficient cholesterol uptake.

An orphaned Mce-associated membrane protein of Mycobacterium tuberculosis is a virulence factor that stabilizes Mce transporters

Mycobacterium tuberculosis proteins that are exported out of the bacterial cytoplasm are ideally positioned to be virulence factors; however, the functions of individual exported proteins remain largely unknown. Previous studies identified Rv0199 as an exported membrane protein of unknown function. Here, we characterized the role of Rv0199 in M. tuberculosis virulence using an aerosol model of murine infection. Rv0199 appears to be a member of a Mce-associated membrane (Mam) protein family leading us to rename it OmamA, for orphaned Mam protein A. Consistent with a role in Mce transport, we showed OmamA is required for cholesterol import, which is a Mce4-dependent process. We further demonstrated a function for OmamA in stabilizing protein components of the Mce1 transporter complex. These results indicate a function of OmamA in multiple Mce transporters and one that may be analogous to the role of VirB8 in stabilizing Type IV secretion systems, as structural similarities between Mam proteins and VirB8 proteins are predicted by the Phyre 2 program. In this study, we provide functional information about OmamA and shed light on the function of Mam family proteins in Mce transporters.

Comparative genomics between human and animal associated subspecies of the Mycobacterium avium complex: a basis for pathogenicity

Background

A human isolate of Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis 43525) was sequenced and compared genomically to other mycobacterial pathogens. M. paratuberculosis 43525 was recently isolated from a patient with ulcerative colitis and belongs to the M. avium complex, a group known to infect both humans and animals. While M. paratuberculosis is a known pathogen of livestock, there are only 20 human isolates from the last 20 years, therefore we took the opportunity to perform a whole genome comparison between human and animal mycobacterial pathogens. We also compared virulence determinants such as the mycobactin cluster, PE/PPE genes and mammalian cell entry (mce) operons between MAC subspecies that infect animals and those that infect humans. M. tuberculosis was also included in these analyses given its predominant role as a human pathogen.

Results

This genome comparison showed the PE/PPE profile of M. paratuberculosis 43525 to be largely the same as other M. paratuberculosis isolates, except that it had one PPE and one PE_PGRS protein that are only present in human MAC strains and M. tuberculosis. PE/PPE proteins that were unique to M. paratuberculosis 43525, M. avium subsp. hominissuis and a caprine M. paratuberculosis isolate, were also identified. In addition, the mycobactin cluster differed between human and animal isolates and a unique mce operon flanked by two mycobactin genes, mbtA and mbtJ, was identified in all available M. paratuberculosis genomes.

Conclusions

Despite the whole genome comparison placing M. paratuberculosis 43525 as closely related to bovine M. paratuberculosis, key virulence factors were similar to human mycobacterial pathogens. This study highlights key factors of mycobacterial pathogenesis in humans and forms the basis for future functional studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1889-2) contains supplementary material, which is available to authorized users.

Label-free Quantitative Proteomics Reveals a Role for the Mycobacterium tuberculosis SecA2 Pathway in Exporting Solute Binding Proteins and Mce Transporters to the Cell Wall

Mycobacterium tuberculosis is an example of a bacterial pathogen with a specialized SecA2-dependent protein export system that contributes to its virulence. Our understanding of the mechanistic basis of SecA2-dependent export and the role(s) of the SecA2 pathway in M. tuberculosis pathogenesis has been hindered by our limited knowledge of the proteins exported by the pathway. Here, we set out to identify M. tuberculosis proteins that use the SecA2 pathway for their export from the bacterial cytoplasm to the cell wall. Using label-free quantitative proteomics involving spectral counting, we compared the cell wall and cytoplasmic proteomes of wild type M. tuberculosis to that of a ΔsecA2 mutant. This work revealed a role for the M. tuberculosis SecA2 pathway in the cell wall localization of solute binding proteins that work with ABC transporters to import solutes. Another discovery was a profound effect of SecA2 on the cell wall localization of the Mce1 and Mce4 lipid transporters, which contribute to M. tuberculosis virulence. In addition to the effects on solute binding proteins and Mce transporter export, our label-free quantitative analysis revealed an unexpected relationship between SecA2 and the hypoxia-induced DosR regulon, which is associated with M. tuberculosis latency. Nearly half of the transcriptionally controlled DosR regulon of cytoplasmic proteins were detected at higher levels in the ΔsecA2 mutant versus wild type M. tuberculosis. By increasing the list of M. tuberculosis proteins known to be affected by the SecA2 pathway, this study expands our appreciation of the types of proteins exported by this pathway and guides our understanding of the mechanism of SecA2-dependent protein export in mycobacteria. At the same time, the newly identified SecA2-dependent proteins are helpful for understanding the significance of this pathway to M. tuberculosis virulence and physiology.

Complete genome sequence and comparative genomic analysis of Mycobacterium massiliense JCM 15300 in the Mycobacterium abscessus group reveal a conserved genomic island MmGI-1 related to putative lipid metabolism

Mycobacterium abscessus group subsp., such as M. massiliense, M. abscessus sensu stricto and M. bolletii, are an environmental organism found in soil, water and other ecological niches, and have been isolated from respiratory tract infection, skin and soft tissue infection, postoperative infection of cosmetic surgery. To determine the unique genetic feature of M. massiliense, we sequenced the complete genome of M. massiliense type strain JCM 15300 (corresponding to CCUG 48898). Comparative genomic analysis was performed among Mycobacterium spp. and among M. abscessus group subspp., showing that additional ß-oxidation-related genes and, notably, the mammalian cell entry (mce) operon were located on a genomic island, M. massiliense Genomic Island 1 (MmGI-1), in M. massiliense. In addition, putative anaerobic respiration system-related genes and additional mycolic acid cyclopropane synthetase-related genes were found uniquely in M. massiliense. Japanese isolates of M. massiliense also frequently possess the MmGI-1 (14/44, approximately 32%) and three unique conserved regions (26/44; approximately 60%, 34/44; approximately 77% and 40/44; approximately 91%), as well as isolates of other countries (Malaysia, France, United Kingdom and United States). The well-conserved genomic island MmGI-1 may play an important role in high growth potential with additional lipid metabolism, extra factors for survival in the environment or synthesis of complex membrane-associated lipids. ORFs on MmGI-1 showed similarities to ORFs of phylogenetically distant M. avium complex (MAC), suggesting that horizontal gene transfer or genetic recombination events might have occurred within MmGI-1 among M. massiliense and MAC.

Deciphering the transcriptional regulation of cholesterol catabolic pathway in mycobacteria: identification of the inducer of KstR repressor

Cholesterol degradation plays a prominent role in Mycobacterium tuberculosis infection; therefore, to develop new tools to combat this disease, we need to decipher the components comprising and regulating the corresponding pathway. A TetR-like repressor (KstR) regulates the upper part of this complex catabolic pathway, but the induction mechanism remains unknown. Using a biophysical approach, we have discovered that the inducer molecule of KstR in M. smegmatis mc(2)155 is not cholesterol but 3-oxo-4-cholestenoic acid, one of the first metabolic intermediates. Binding this compound induces dramatic conformational changes in KstR that promote the KstR-DNA interaction to be released from the operator, retaining its dimeric state. Our findings suggest a regulatory model common to all cholesterol degrading bacteria in which the first steps of the pathway are critical to its mineralization and explain the high redundancy of the enzymes involved in these initial steps.

Role of the Mce1 transporter in the lipid homeostasis of Mycobacterium tuberculosis

Tuberculosis is one of the leading causes of mortality throughout the world. Mycobacterium tuberculosis, the causative agent of human tuberculosis, has developed several strategies involving proteins and other compounds known collectively as virulence factors to subvert human host defences and invade the human host. The Mce proteins are among these virulence-related proteins and are encoded by the mce1, mce2, mce3 and mce4 operons in the genome of M. tuberculosis. It has been proposed that these operons encode ABC-like lipid transporters; however, the nature of their substrates has only been revealed in the case of the Mce4 proteins. Here we found that the knockout of the mce1 operon alters the lipid profile of M. tuberculosis H37Rv and the uptake of palmitic acid. Thin layer chromatography and liquid chromatography-mass spectrometry analysis showed that the mce1 mutant accumulates more mycolic acids than the wild type and complemented strains. Interestingly, this accumulation of mycolic acid is exacerbated when bacteria are cultured in the presence of palmitic acid or arachidonic acid. These results suggest that the mce1 operon may serve as a mycolic acid re-importer.

Comparative genome analysis of Mycobacterium avium revealed genetic diversity in strains that cause pulmonary and disseminated disease

Mycobacterium avium complex (MAC) infection causes disseminated disease in immunocompromised hosts, such as human immunodeficiency virus (HIV)-positive patients, and pulmonary disease in persons without systemic immunosuppression, which has been increasing in many countries. In Japan, the incidence of pulmonary MAC disease caused by M. avium is about 7 times higher than that caused by M. intracellulare. To explore the bacterial factors that affect the pathological state of MAC disease caused by M. avium, we determined the complete genome sequence of the previously unreported M. avium subsp. hominissuis strain TH135 isolated from a HIV-negative patient with pulmonary MAC disease and compared it with the known genomic sequence of M. avium strain 104 derived from an acquired immunodeficiency syndrome patient with MAC disease. The genome of strain TH135 consists of a 4,951,217-bp circular chromosome with 4,636 coding sequences. Comparative analysis revealed that 4,012 genes are shared between the two strains, and strains TH135 and 104 have 624 and 1,108 unique genes, respectively. Many strain-specific regions including virulence-associated genes were found in genomes of both strains, and except for some regions, the G+C content in the specific regions was low compared with the mean G+C content of the corresponding chromosome. Screening of clinical isolates for genes located in the strain-specific regions revealed that the detection rates of strain TH135-specific genes were relatively high in specimens isolated from pulmonary MAC disease patients, while, those of strain 104-specific genes were relatively high in those from HIV-positive patients. Collectively, M. avium strains that cause pulmonary and disseminated disease possess genetically distinct features, and it suggests that the acquisition of specific genes during strain evolution has played an important role in the pathological manifestations of MAC disease.

Lipid Droplets and Mycobacterium leprae Infection

Leprosy is a chronic infectious disease and is a major source of morbidity in developing countries. Leprosy is caused by the obligate intracellular bacterium Mycobacterium leprae, which infects as primary target Schwann cells. Lepromatous leprosy exhibits multiple lesions of the skin, eyes, nerves, and lymph nodes. The sites of infection are characterized by the presence of foamy macrophages, fully packed with lipid droplets (LDs), which are induced by M. leprae. In the last years, it has become evident that M. tuberculosis imports lipids from foamy macrophages and is dependent on fatty acids for growth in infected macrophages. M. leprae seems to have similar mechanisms for scavenging lipids from the host. But due to the inability to culture M. leprae on laboratory media, research progresses only slowly. However, in the last years, substantial progress has been made in the field of lipid metabolism in M. leprae. Herein, we will present and summarize the lipid droplets formation and the metabolism of lipids during M. leprae infection.

Cytosolic lipid inclusions formed during infection by viral and bacterial pathogens

Lipid inclusions play an important role in several pathological processes. Intracellular bacterial pathogens, such as members of the Mycobacterium and Chlamydia species are able to trigger the formation of lipid-laden foamy macrophages. Lipid droplet accumulation in the host constitutes a reservoir used by the bacilli for long-term persistence. Viruses need lipid droplets as assembly platform. We present the current knowledge about structural, functional and regulatory aspects of lipid inclusions.