Extensive genomic diversity among Mycobacterium marinum strains revealed by whole genome sequencing

Revised whole genome and DNA methylome of Mycobacterium marinum type strain ATCC 927T

Mycobacterium marinum, a slow-growing Actinobacterium, typically induces tuberculosis-like disease in fish. Here, we report a new reference sequence for M. marinum ATCC 927T, along with its DNA methylome. This aims to maximize the research potential of this type strain and facilitates investigations into the pathomechanisms of human tuberculosis.

Temporal genome-wide fitness analysis of Mycobacterium marinum during infection reveals the genetic requirement for virulence and survival in amoebae and microglial cells

Tuberculosis remains the most pervasive infectious disease and the recent emergence of drug-resistant strains emphasizes the need for more efficient drug treatments. A key feature of pathogenesis, conserved between the human pathogen Mycobacterium tuberculosis and the model pathogen Mycobacterium marinum, is the metabolic switch to lipid catabolism and altered expression of virulence genes at different stages of infection. This study aims to identify genes involved in sustaining viable intracellular infection. We applied transposon sequencing (Tn-Seq) to M. marinum, an unbiased genome-wide strategy combining saturation insertional mutagenesis and high-throughput sequencing. This approach allowed us to identify the localization and relative abundance of insertions in pools of transposon mutants. Gene essentiality and fitness cost of mutations were quantitatively compared between in vitro growth and different stages of infection in two evolutionary distinct phagocytes, the amoeba Dictyostelium discoideum and the murine BV2 microglial cells. In the M. marinum genome, 57% of TA sites were disrupted and 568 genes (10.2%) were essential, which is comparable to previous Tn-Seq studies on M. tuberculosis and M. bovis. Major pathways involved in the survival of M. marinum during infection of D. discoideum are related to DNA damage repair, lipid and vitamin metabolism, the type VII secretion system (T7SS) ESX-1, and the Mce1 lipid transport system. These pathways, except Mce1 and some glycolytic enzymes, were similarly affected in BV2 cells. These differences suggest subtly distinct nutrient availability or requirement in different host cells despite the known predominant use of lipids in both amoeba and microglial cells.IMPORTANCEThe emergence of biochemically and genetically tractable host model organisms for infection studies holds the promise to accelerate the pace of discoveries related to the evolution of innate immunity and the dissection of conserved mechanisms of cell-autonomous defenses. Here, we have used the genetically and biochemically tractable infection model system Dictyostelium discoideum/Mycobacterium marinum to apply a genome-wide transposon-sequencing experimental strategy to reveal comprehensively which mutations confer a fitness advantage or disadvantage during infection and compare these to a similar experiment performed using the murine microglial BV2 cells as host for M. marinum to identify conservation of virulence pathways between hosts.

Immobilization of rough morphotype Mycolicibacterium neoaurum R for androstadienedione production

OBJECTIVES

Enhance the androstadienedione (Androst-1,4-diene-3,17-dione, ADD) production of rough morphotype Mycolicibacterium neoaurum R by repeated-batch fermentation of immobilized cells.

RESULTS

M. neoaurum R was a rough colony morphotype variant, obtained from the routine plating of smooth M. neoaurum strain CICC 21097. M. neoaurum R showed rougher cell surface and aggregated in broth. The ADD production of M. neoaurum R was notably lower than that of M. neoaurum CICC 21097 during the free cell fermentation, but the yield gap could be erased after proper cell immobilization. Subsequently, repeated-batch fermentation of immobilized M. neoaurum R was performed to shorten the production cycle and enhance the bio-production efficiency of ADD. Through the optimization of the immobilization carriers and the co-solvents for phytosterols, the ADD productivity of M. neoaurum R immobilized by semi-expanded perlite reached 0.075 g/L/h during the repeated-batch fermentation for 40 days.

CONCLUSIONS

The ADD production of the rough-type M. neoaurum R was notably enhanced by the immobilization onto semi-expanded perlite. Moreover, the ADD batch yields of M. neoaurum R immobilized by semi-expanded perlite were maintained at high levels during the repeated-batch fermentation.

Complete Genome Sequence of Mycobacterium marinum Strain 050012 Isolated from Infected Skin Tissue

We report the complete genome sequence of a Mycobacterium marinum strain, which was isolated from skin tissue of a wound infection. This strain was subjected to short- and long-read sequencing. Its complete genome contains a single 6,393,703-bp circular chromosome. Phylogenomic analysis of all M. marinum genomes assigned this strain to cluster I.

MGIT Enriched Shotgun Metagenomics for Routine Identification of Nontuberculous Mycobacteria: a Route to Personalized Health Care

Currently, nontuberculous mycobacteria (NTM) are identified using small genomic regions, and species-level identification is often not possible. We introduce a next-generation sequencing (NGS) workflow that identifies mycobacteria to (sub)species level on the basis of the whole genome extracted from enriched shotgun metagenomic data. This technique is used to study the association between genotypes and clinical manifestations to pave the way to more personalized health care. Two sets of clinical isolates (explorative set [n = 212] and validation set [n = 235]) were included. All data were analyzed using a custom pipeline called MyCodentifier. Sequences were matched against a custom hsp65 database (NGS-hsp65) and whole-genome database (NGS-WG) created based on the phylogeny presented by Tortoli et al. (E. Tortoli, T. Fedrizzi, C. J. Meehan, A. Trovato, et al., Infect Genet Evol 56:19-25, 2017, https://doi.org/10.1016/j.meegid.2017.10.013). Lastly, phylogenetic analysis was performed and correlated with clinical manifestation. In the explorative set, we observed 98.6% agreement between the line probe assay and the NGS-hsp65 database. In the validation set, 99.1% agreement between the NGS-WG and NGS-hsp65 databases was seen on the complex level. We identified a cluster of Mycobacterium marinum isolates not represented by the Tortoli et al. phylogeny. Phylogenetic analysis of M. avium complex isolates confirmed misclassification of M. timonense and M. bouchedurhonense and identified subclusters within M. avium although no correlation with clinical manifestation was observed. We performed routine NGS to identify NTM from MGIT enriched shotgun metagenomic data. Phylogenetic analyses identified subtypes of M. avium, but in our set of isolates no correlation with clinical manifestation was found. However, this NGS workflow paves a way for more personalized health care in the future.

The ESX-1 Substrate PPE68 Has a Key Function in ESX-1-Mediated Secretion in Mycobacterium marinum

Mycobacteria use specialized type VII secretion systems (T7SSs) to secrete proteins across their diderm cell envelope. One of the T7SS subtypes, named ESX-1, is a major virulence determinant in pathogenic species such as Mycobacterium tuberculosis and the fish pathogen Mycobacterium marinum. ESX-1 secretes a variety of substrates, called Esx, PE, PPE, and Esp proteins, at least some of which are folded heterodimers. Investigation into the functions of these substrates is problematic, because of the intricate network of codependent secretion between several ESX-1 substrates. Here, we describe the ESX-1 substrate PPE68 as essential for secretion of the highly immunogenic substrates EsxA and EspE via the ESX-1 system in M. marinum. While secreted PPE68 is processed on the cell surface, the majority of cell-associated PPE68 of M. marinum and M. tuberculosis is present in a cytosolic complex with its PE partner and the EspG₁ chaperone. Interfering with the binding of EspG₁ to PPE68 blocked its export and the secretion of EsxA and EspE. In contrast, esxA was not required for the secretion of PPE68, revealing a hierarchy in codependent secretion. Remarkably, the final 10 residues of PPE68, a negatively charged domain, seem essential for EspE secretion, but not for the secretion of EsxA and of PPE68 itself. This indicates that distinctive domains of PPE68 are involved in secretion of the different ESX-1 substrates. Based on these findings, we propose a mechanistic model for the central role of PPE68 in ESX-1-mediated secretion and substrate codependence. IMPORTANCE Pathogenic mycobacteria, such Mycobacterium tuberculosis and Mycobacterium marinum, use a type VII secretion system (T7SS) subtype, called ESX-1, to mediate intracellular survival via phagosomal rupture and subsequent translocation of the mycobacterium to the host cytosol. Identifying the ESX-1 substrate that is responsible for this process is problematic because of the intricate network of codependent secretion between ESX-1 substrates. Here, we show the central role of the ESX-1 substrate PPE68 for the secretion of ESX-1 substrates in Mycobacterium marinum. Unravelling the mechanism of codependent secretion will aid the functional understanding of T7SSs and will allow the analysis of the individual roles of ESX-1 substrates in the virulence caused by the significant human pathogen Mycobacterium tuberculosis.

Comparative genome analysis of mycobacteria focusing on tRNA and non-coding RNA

BACKGROUND

The Mycobacterium genus encompasses at least 192 named species, many of which cause severe diseases such as tuberculosis. Non-tuberculosis mycobacteria (NTM) can also infect humans and animals. Some are of emerging concern because they show high resistance to commonly used antibiotics while others are used and evaluated in bioremediation or included in anticancer vaccines.

RESULTS

We provide the genome sequences for 114 mycobacterial type strains and together with 130 available mycobacterial genomes we generated a phylogenetic tree based on 387 core genes and supported by average nucleotide identity (ANI) data. The 244 genome sequences cover most of the species constituting the Mycobacterium genus. The genome sizes ranged from 3.2 to 8.1 Mb with an average of 5.7 Mb, and we identified 14 new plasmids. Moreover, mycobacterial genomes consisted of phage-like sequences ranging between 0 and 4.64% dependent on mycobacteria while the number of IS elements varied between 1 and 290. Our data also revealed that, depending on the mycobacteria, the number of tRNA and non-coding (nc) RNA genes differ and that their positions on the chromosome varied. We identified a conserved core set of 12 ncRNAs, 43 tRNAs and 18 aminoacyl-tRNA synthetases among mycobacteria.

CONCLUSIONS

Phages, IS elements, tRNA and ncRNAs appear to have contributed to the evolution of the Mycobacterium genus where several tRNA and ncRNA genes have been horizontally transferred. On the basis of our phylogenetic analysis, we identified several isolates of unnamed species as new mycobacterial species or strains of known mycobacteria. The predicted number of coding sequences correlates with genome size while the number of tRNA, rRNA and ncRNA genes does not. Together these findings expand our insight into the evolution of the Mycobacterium genus and as such they establish a platform to understand mycobacterial pathogenicity, their evolution, antibiotic resistance/tolerance as well as the function and evolution of ncRNA among mycobacteria.

Genomic Degeneration and Reduction in the Fish Pathogen Mycobacterium shottsii

Mycobacterium shottsii is a dysgonic, nonpigmented mycobacterium originally isolated from diseased striped bass (Morone saxatilis) in the Chesapeake Bay, USA. Genomic analysis reveals that M. shottsii is a Mycobacterium ulcerans/Mycobacterium marinum clade (MuMC) member, but unlike the superficially similar M. pseudoshottsii, also isolated from striped bass, it is not an M. ulcerans ecovar, instead belonging to a transitional group of strains basal to proposed "Aronson" and "M" lineages. Although phylogenetically distinct from the human pathogen M. ulcerans, the M. shottsii genome shows parallel but nonhomologous genomic degeneration, including massive accumulation of pseudogenes accompanied by proliferation of unique insertion sequences (ISMysh01, ISMysh03), large-scale deletions, and genomic reorganization relative to typical M. marinum strains. Coupled with its observed ecological characteristics and loss of chromogenicity, the genomic structure of M. shottsii is suggestive of evolution toward a state of obligate pathogenicity, as observed for other Mycobacterium spp., including M. ulcerans, M. tuberculosis, and M. leprae. IMPORTANCE Morone saxatilis (striped bass) is an ecologically and economically important finfish species on the United States east coast. Mycobacterium shottsii and Mycobacterium pseudoshottsii were originally described in the early 2000s as novel species from outbreaks of visceral and dermal mycobacteriosis in this species. Biochemical and genetic characterization place these species within the Mycobacterium ulcerans/M. marinum clade (MuMC), and M. pseudoshottsii has been proposed as an ecovar of M. ulcerans. Here, we describe the complete genome of M. shottsii, demonstrating that it is clearly not an M. ulcerans ecovar; however, it has undergone parallel genomic modification suggestive of a transition to obligate pathogenicity. As in M. ulcerans, the M. shottsii genome demonstrates widespread pseudogene formation driven by proliferation of insertion sequences, as well as genomic reorganization. This work clarifies the phylogenetic position of M. shottsii relative to other MuMC members and provides insight into processes shaping its genomic structure.

New insights about Haplosporidium pinnae and the pen shell Pinna nobilis mass mortality events

Since early autumn 2016, Mass Mortality Events (MME) have drastically impacted the population of the fan mussel Pinna nobilis in the Mediterranean Sea. Haplosporidium pinnae, a newly described Haplosporidian species, has been considered the causative agent of the mortality outbreaks in association to opportunistic bacterial pathogens. In the present study, we first reported a cytological description of H. pinnae in moribund specimens of P. nobilis which were collected in the Gulf of Taranto (Ionian Sea, Italy) during summer 2018. Different life-cycle stages of the parasite, including uni- and binucleate cells, small plasmodia, big multinucleate plasmodia and sporocysts with spores, were detected in all the examined animals and most of the parasite cells were present in gills, mantle and digestive gland, while the spores were found only in the latter organ. Histology and molecular biology were also performed, confirming the nature of the infectious agent, as already reported in the area. Additionally, molecular study revealed the presence of the Mycobacterium ulcerans - M. marinum complex but no evident macroscopical or microscopical lesions, just as no bacteria referred to Mycobacterium were observed. In conclusion, the present study aimed to provide further contributions to the understanding of the mortality of P. nobilis, pointing on the role of the cytological method of investigation both for diagnostic and epidemiological purposes, and discussing about the current epidemic situation in the Adriatic sea.

High female mortality caused by an atypical Mycobacterium species closely related to the Mycobacterium ulcerans-marinum complex in a colony of bearded dragons (Pogona vitticeps)

A commercial breeding colony of bearded dragons (Pogona vitticeps) experienced an increase in mortality that affected females only. Before death, the animals had lost appetite and weight, were dehydrated, and some had labored breathing. Necropsy revealed granulomas in many organs (ovaries, lungs, liver, kidneys, heart, bone marrow) in which numerous acid-fast bacteria were identified. Bacterial isolation confirmed Mycobacterium spp., which was identified by whole genome sequencing as closely related to the Mycobacterium ulcerans-marinum complex. Due to the zoonotic potential of this bacterium and the poor prognosis for the remaining sick animals, the entire colony was culled and 7 animals were evaluated. The possible routes for introduction of this bacterium, the female predisposition to the disease, as well as the zoonotic potential of this microorganism are discussed. Key clinical message: An atypical Mycobacterium species closely related to Mycobacterium ulcerans-marinum complex can cause high female morality in captive bearded dragons.

Whole-Genome sequencing and comparative genomics of Mycobacterium spp. from farmed Atlantic and coho salmon in Chile

Several members of the Mycobacterium genus cause invasive infections in humans and animals. According to a recent phylogenetic analysis, some strains of Mycobacterium salmoniphilum (Msal), which are the main culprit in bacterial outbreaks in freshwater fish aquaculture, have been assigned to a separate branch containing Mycobacterium franklinii (Mfra), another species that causes infections in humans. However, this genus is little studied in an aquaculture context. Here, we isolated four Mycobacterium spp. strains from freshwater cultures of Atlantic and coho salmon in Chile and performed whole-genome sequencing for deep genomic characterization. In addition, we described the gross pathology and histopathology of the outbreaks. Several bioinformatic analyses were performed using the genomes of these four Mycobacterium isolates in conjunction with those of Msal strains, four Msal-like strains, and one Mfra strains, plus 17 other publicly available Mycobacterium genomes. We found that three isolates are clustered into the Msal branch, whereas one isolate clustered with the Mfra/Msal-like strains. We further evaluated the presence of virulence and antimicrobial resistance genes and observed that the four isolates were closely related to the Msal and Msal-like taxa and carried several antimicrobial resistance and virulence genes that are similar to those of other pathogenic members of the Mycobacterium clade. Altogether, our characterization Msal and Msal-like presented here shed new light on the basis of mycobacteriosis provides quantitative evidence that Mycobacterium strains are a potential risk for aquaculture asetiological agents of emerging diseases, and highlight their biological scopes in the aquaculture industry.

Intracellular localization of the mycobacterial stressosome complex

Microorganisms survive stresses by alternating the expression of genes suitable for surviving the immediate and present danger and eventually adapt to new conditions. Many bacteria have evolved a multiprotein "molecular machinery" designated the "Stressosome" that integrates different stress signals and activates alternative sigma factors for appropriate downstream responses. We and others have identified orthologs of some of the Bacillus subtilis stressosome components, RsbR, RsbS, RsbT and RsbUVW in several mycobacteria and we have previously reported mutual interactions among the stressosome components RsbR, RsbS, RsbT and RsbUVW from Mycobacterium marinum. Here we provide evidence that "STAS" domains of both RsbR and RsbS are important for establishing the interaction and thus critical for stressosome assembly. Fluorescence microscopy further suggested co-localization of RsbR and RsbS in multiprotein complexes visible as co-localized fluorescent foci distributed at scattered locations in the M. marinum cytoplasm; the number, intensity and distribution of such foci changed in cells under stressed conditions. Finally, we provide bioinformatics data that 17 (of 244) mycobacteria, which lack the RsbRST genes, carry homologs of Bacillus cereus genes rsbK and rsbM indicating the existence of alternative σ^F activation pathways among mycobacteria.

Soil Metagenomics Reveals Effects of Continuous Sugarcane Cropping on the Structure and Functional Pathway of Rhizospheric Microbial Community

The continuous cropping of plants can result in the disruption of the soil microbial community and caused significant declines in yields. However, there are few reports on the effects of continuous cropping of sugarcane on the microbial community structure and functional pathway. In the current study, we analyzed the structural and functional changes of microbial community structure in the rhizospheric soil of sugarcane in different continuous cropping years using Illumina Miseq high-throughput sequencing and metagenomics analysis. We collected rhizosphere soils from fields of no continuous cropping history (NCC), 10 years of continuous cropping (CC10), and 30 years of continuous cropping (CC30) periods in the Fujian province. The results demonstrated that continuous sugarcane cropping resulted in significant changes in the physicochemical properties of soil and the composition of soil bacterial and fungal communities. With the continuous cropping, the crop yield dramatically declined from NCC to CC30. Besides, the redundancy analysis (RDA) of the dominant bacterial and fungal phyla and soil physicochemical properties revealed that the structures of the bacterial and fungal communities were mainly driven by pH and TS. Analysis of potential functional pathways during the continuous cropping suggests that different KEGG pathways were enriched in different continuous cropping periods. The significant reduction of bacteria associated with rhizospheric soil nitrogen and sulfur cycling functions and enrichment of pathogenic bacteria may be responsible for the reduction of effective nitrogen and total sulfur content in rhizospheric soil of continuous sugarcane as well as the reduction of sugarcane yield and sugar content. Additionally, genes related to nitrogen and sulfur cycling were identified in our study, and the decreased abundance of nitrogen translocation genes and AprAB and DsrAB in the dissimilatory sulfate reduction pathway could be the cause of declined biomass. The findings of this study may provide a theoretical basis for uncovering the mechanism of obstacles in continuous sugarcane cropping and provide better guidance for sustainable development of the sugarcane.

Disseminated Mycobacterium marinum in Human Immunodeficiency Virus Unmasked by Immune Reconstitution Inflammatory Syndrome

Distinguishing disseminated Mycobacterium marinum from multifocal cutaneous disease in persons with human immunodeficiency virus/AIDS can present a diagnostic challenge, especially in the context of immune reconstitution inflammatory syndrome (IRIS). In this work, we demonstrate the utility of flow cytometry and whole genome sequencing (WGS) to diagnose disseminated M. marinum unmasked by IRIS following initiation of antiretroviral therapy. Flow cytometry demonstrated robust cytokine production by CD4 T cells in response to stimulation with M. marinum lysate. WGS of isolates from distinct lesions was consistent with clonal dissemination, supporting that preexisting disseminated M. marinum disease was uncovered by inflammatory manifestations, consistent with unmasking mycobacterial IRIS.

Mycobacterium marinum infection simulating chromomycosis: a case report

Skins infections caused by Mycobacterium marinum occur only rarely. We report one case of chronic and extensive M. marinum cutaneous infection simulating chromoblastomycosis and review the pertinent literature. A 52-year-old farmer reported a 32-year chronic skin problem on his right lower limb, resulting from contact with cacti. It consisted of skin lesion presenting with dyschromic atrophic center plate and verrucous borders with hematic crusts, extending from the knee anteriorly to the inferior third of the right leg. Mycobacterium marinum infection was detected by histopathological examination of a skin fragment, culture for mycobacteria and genetic mapping of the culture material. The patient was successfully treated with Ethambutol, Rifampicin and Trimethoprim-Sulfamethoxazole. The clinical and histopathological findings of M. marinum infection is nonspecific showing clinical polymorphism and bacilli are rarely evident on histopathological examination. Given these difficulties, it is essential to perform tissue culture in a suspicious case and it is important keep this infection in mind in patients with long-lasting indolent verrucous lesions and a history of exposure to sea water, freshwater, aquaria or fish.

Investigating hospital Mycobacterium chelonae infection using whole genome sequencing and hybrid assembly

Mycobacterium chelonae is a rapidly growing nontuberculous mycobacterium that is a common cause of nosocomial infections. Here we describe investigation of a possible nosocomial transmission of M. chelonae at the Hospital of the University of Pennsylvania (HUP). M. chelonae strains with similar high-level antibiotic resistance patterns were isolated from two patients who developed post-operative infections at HUP in 2017, suggesting a possible point source infection. The isolates, along with other clinical isolates from other patients, were sequenced using the Illumina and Oxford Nanopore technologies. The resulting short and long reads were hybrid assembled into draft genomes. The genomes were compared by quantifying single nucleotide variants in the core genome and assessed using a control dataset to quantify error rates in comparisons of identical genomes. We show that all M. chelonae isolates tested were highly dissimilar, as indicated by high pairwise SNV values, consistent with environmental acquisition and not a nosocomial point source. Our control dataset determined a threshold for evaluating identity between strains while controlling for sequencing error. Finally, antibiotic resistance genes were predicted for our isolates, and several single nucleotide variants were identified that have the potential to modulated drug resistance.

Insight into the biology of Mycobacterium mucogenicum and Mycobacterium neoaurum clade members

Nontuberculous mycobacteria, NTM, are of growing concern and among these members of the Mycobacterium mucogenicum (Mmuc) and Mycobacterium neoaurum (Mneo) clades can cause infections in humans and they are resistant to first-line anti-tuberculosis drugs. They can be isolated from different ecological niches such as soil, tap water and ground water. Mycobacteria, such as Mmuc and Mneo, are classified as rapid growing mycobacteria, RGM, while the most familiar, Mycobacterium tuberculosis, belongs to the slow growing mycobacteria, SGM. Modern “omics” approaches have provided new insights into our understanding of the biology and evolution of this group of bacteria. Here we present comparative genomics data for seventeen NTM of which sixteen belong to the Mmuc- and Mneo-clades. Focusing on virulence genes, including genes encoding sigma/anti-sigma factors, serine threonine protein kinases (STPK), type VII (ESX genes) secretion systems and mammalian cell entry (Mce) factors we provide insight into their presence as well as phylogenetic relationship in the case of the sigma/anti-sigma factors and STPKs. Our data further suggest that these NTM lack ESX-5 and Mce2 genes, which are known to affect virulence. In this context, Mmuc- and Mneo-clade members lack several of the genes in the glycopeptidolipid (GLP) locus, which have roles in colony morphotype appearance and virulence. For the M. mucogenicum type strain, Mmuc^T, we provide RNASeq data focusing on mRNA levels for sigma factors, STPK, ESX proteins and Mce proteins. These data are discussed and compared to in particular the SGM and fish pathogen Mycobacterium marinum. Finally, we provide insight into as to why members of the Mmuc- and Mneo-clades show resistance to rifampin and isoniazid, and why Mmuc^T forms a rough colony morphotype.

Extended insight into the Mycobacterium chelonae-abscessus complex through whole genome sequencing of Mycobacterium salmoniphilum outbreak and Mycobacterium salmoniphilum-like strains

Members of the Mycobacterium chelonae-abscessus complex (MCAC) are close to the mycobacterial ancestor and includes both human, animal and fish pathogens. We present the genomes of 14 members of this complex: the complete genomes of Mycobacterium salmoniphilum and Mycobacterium chelonae type strains, seven M. salmoniphilum isolates, and five M. salmoniphilum-like strains including strains isolated during an outbreak in an animal facility at Uppsala University. Average nucleotide identity (ANI) analysis and core gene phylogeny revealed that the M. salmoniphilum-like strains are variants of the human pathogen Mycobacterium franklinii and phylogenetically close to Mycobacterium abscessus. Our data further suggested that M. salmoniphilum separates into three branches named group I, II and III with the M. salmoniphilum type strain belonging to group II. Among predicted virulence factors, the presence of phospholipase C (plcC), which is a major virulence factor that makes M. abscessus highly cytotoxic to mouse macrophages, and that M. franklinii originally was isolated from infected humans make it plausible that the outbreak in the animal facility was caused by a M. salmoniphilum-like strain. Interestingly, M. salmoniphilum-like was isolated from tap water suggesting that it can be present in the environment. Moreover, we predicted the presence of mutational hotspots in the M. salmoniphilum isolates and 26% of these hotspots overlap with genes categorized as having roles in virulence, disease and defense. We also provide data about key genes involved in transcription and translation such as sigma factor, ribosomal protein and tRNA genes.

Nontuberculous mycobacteria: Insights on taxonomy and evolution

Seventy years have passed since Ernest H. Runyon presented a phenotypic classification approach for nontuberculous mycobacteria (NTM), primarily as a starting point in trying to understand their clinical relevance. From numerical taxonomy (biochemical testing) to 16S rRNA gene sequencing to whole genome sequencing (WGS), our understanding of NTM has also evolved. Novel species are described at a rapid pace, while taxonomical relationships are re-defined in large part due to the accessibility of WGS. The evolutionary course of clonal complexes within species is better known for some NTM and less for others. In contrast with M. tuberculosis, much is left to learn about NTM as a whole.