Osteomyelitis caused by Veillonella species: Case report and review of the literature

Role of Oral Veillonella Species in Predicting Surgical Site Infections After Maxillofacial Trauma: A Prospective Observational Study

INTRODUCTION

There are comparatively fewer surgical site infections after craniofacial trauma than after trauma to the extremities, and the etiology is complex. Gram-negative facultative anaerobic bacteria Veillonella is a common commensal in the oral cavity and has been linked to osteomyelitis and surgical site infections in prosthetic joint infections. They serve as early biological indicators.

AIMS/OBJECTIVES

This study aims to assess the presence of Veillonella in patients presenting with maxillofacial trauma, to document the difference in colony count in patients requiring surgical intervention at different time intervals as against patients with surgical site infections, and to provide better hospital care and management so as to improve the standard of care with an attempt to prevent the possibility of postoperative surgical site infections.

METHODOLOGY

In this study, individuals with trauma/fractures of the maxillofacial region requiring surgical intervention at varied time spans, early, intermediate, and late, were included. After obtaining informed consent, the examination was done; the fracture type and site were noted, and a swab was taken on the day of admission, on the day of surgery, and on the day of discharge and given for microbiological evaluation. Findings were recorded.

RESULTS

The primary and secondary objectives of the study were established. The mean colony count in colony-forming units/milliliter for patients undergoing early surgical intervention, on the day of admission, was 2.01E+0.6. On the day of discharge, the mean colony count was 1.51E+0.6. In contrast, for patients with surgical site infection, on the day of admission, the mean was 6.5E+0.7, and on the day of discharge, the mean colony count reduced to 4.01E+0.6. The time-colony-forming unit graph showed a difference in the colony count of Veillonella in patients operated at different time intervals as against patients with surgical site infection and modified relation with a number of other oral commensals. The colony count in patients with osteomyelitis was found and compared.

CONCLUSION

There is a change in the colony count of Veillonella species and its relation to their commensals when intervened at different time intervals. Our study indicates that the estimation of Veillonella species and the colony count could aid in determining the possibility of a surgical site infection. This study also stresses on the appropriate reporting of maxillofacial trauma in cases of a poly-trauma for appropriate management.

Extensive Sequestration Chronic Maxillary Osteomyelitis in an Uncontrolled Diabetic Patient: Comprehensive Case Management of a Rare Entity

The hallmark of osteomyelitis was progressive bone destruction and sequestrum formation. In the underlying disease, like diabetes mellitus, osteomyelitis becomes severe and exacerbates the condition. It was essential for the oral and maxillofacial surgeon to comprehend its complex medical and surgical management to achieve complete disease eradication. The aim of this article was to report a rare case and comprehensive management of extensive sequestrating maxillary osteomyelitis with uncontrolled diabetes mellitus patients. A 58-year-old male patient with pain and swelling accompanied by discharge of pus in the sinistra maxilla region. The systemic disease was identified as uncontrolled diabetes mellitus, and had a history of unhealing wounds 1 year ago after upper left molar extraction. Computed tomography scan result showed extensive sequester formation and bony destruction in the right extending to the left maxilla. Microbial culture results were Klebsiella pneumoniae and Morganella morganii. Subsequently, extensive sequestrectomy and multiple extractions of the involved jaw and teeth were performed after diabetes mellitus was regulated. A suspension suture against oral and nasal mucosa was performed to avoid dead space formation. Comprehensive perioperative management in maxillary osteomyelitis in uncontrolled diabetes mellitus includes sequestrectomy, definitive antibiotic therapy based on culture results, and diabetes regulation to improve the successful management of this case.

Lifestyle patterns influence the composition of the gut microbiome in a healthy Chinese population

High-throughput sequencing allows for the comprehensive analysis of the human intestinal microbiota. However, extensive association analyses between the microbiome and lifestyle differences in the Chinese population are limited. Here, we carried out an independent cohort study-the Chinese Healthy Gut Project (n = 483)-where correlations between the gut microbiota and dietary and lifestyle variables in a healthy Chinese population are defined. We collected both questionnaire data, including basic information and lifestyle and dietary variables, and fecal stools from the enrolled volunteers. We then performed 16S rRNA sequencing on the microbial DNA isolated from the stools to assess the composition of the intestinal microbiota. We found that Prevotella and Bacteroides were the most abundant genera in the healthy Chinese gut microbiome. Additionally, 9 out of 29 clinical and questionnaire-based phenotype covariates were found to be associated with the variation in the composition of the gut microbiota. Among these lifestyle phenotypes, sleep procrastination, negative mood, and drinking habits had the largest effect size. Additionally, an appreciable effect of urbanization was observed, resulting in decreased intra-individual diversity, increased inter-individual diversity, and an increased abundance of the Bacteroides enterotype. The results of this study provide a foundation for assessing the healthy Chinese gut microbiota community structure at baseline in a healthy Chinese population. Furthermore, this study also provides insights into understanding how distinctive living habits influence the relationships between the Chinese gut microbiome and systemic health state.

Translocation of Oral Microbiota into the Pancreatic Ductal Adenocarcinoma Tumor Microenvironment

Oral dysbiosis has long been associated with pancreatic ductal adenocarcinoma (PDAC). In this work, we explore the relationship between the oral and tumor microbiomes of patients diagnosed with PDAC. Salivary and tumor microbiomes were analyzed using a variety of sequencing methods, resulting in a high prevalence and relative abundance of oral bacteria, particularly Veillonella and Streptococcus, within tumor tissue. The most prevalent and abundant taxon found within both saliva and tumor tissue samples, Veillonella atypica, was cultured from patient saliva, sequenced and annotated, identifying genes that potentially contribute to tumorigenesis. High sequence similarity was observed between sequences recovered from patient matched saliva and tumor tissue, indicating that the taxa found in PDAC tumors may derive from the mouth. These findings may have clinical implications in the care and treatment of patients diagnosed with PDAC.

Veillonella atypica causing retropharyngeal abscess: A rare case presentation

Veillonella species are obligate anaerobes which are part of the human oral, gut and vaginal microbiota. The genus Veillonella consists of 16 characterized species. Very few infections due to Veillonella atypica have been reported till date. Here we present a case of retropharyngeal abscess due to this organism in a 55-year-old lady.

Gut bacterial profiles in Parkinson's disease: A systematic review

INTRODUCTION

Recent advances have highlighted the relationships between gut dysbiosis and Parkinson's disease (PD). Microbiota transplantation from PD patients to mice can induce increased alpha-synuclein-mediated motor deficits. Human studies have identified differences in the gut microbiota of PD patients compared to healthy controls. We undertook a systematic review to evaluate the available evidence for the involvement of gut bacteria in the etiology of PD.

METHODS

The PubMed databank, the China National Knowledge Infrastructure databank, and Wanfang Data were searched from inception until June 2021 to identify human case-control studies that investigated relationships between PD and microbiota quantified from feces. We evaluated the resulting studies focusing on bacterial taxa that were different between PD patients and healthy controls.

RESULTS

Twenty-six studies were found in which 53 microbial families and 98 genera exhibited differences between patients with PD and healthy controls. The genera identified by more than two studies as increased in PD were Bifidobacterium, Alistipes, Christensenella, Enterococcus, Oscillospira, Bilophila, Desulfovibrio, Escherichia/Shigella, and Akkermansia, while Prevotella, Blautia, Faecalibacterium, Fusicatenibacter, and Haemophilus had three or more reports of being lower in PD patients. More than one report demonstrated that Bacteroides, Odoribacter, Parabacteroides, Butyricicoccus, Butyrivibrio, Clostridium, Coprococcus, Lachnospira, Lactobacillus, Megasphaera, Phascolarctobacterium, Roseburia, Ruminococcus, Streptococcus, and Klebsiella were altered in both directions.

CONCLUSION

Our review shows that the involvement of the gut microbiome in the etiology of PD may involve alterations of short-chain fatty acids (SCFAs)-producing bacteria and an increase in putative gut pathobionts. SCFAs-producing bacteria may vary above or below an "optimal range," causing imbalances. Considering that Bifidobacterium, Lactobacillus, and Akkermansia are beneficial for human health, increased Bifidobacterium and Lactobacillus in the PD gut microbiome may be associated with PD medications, especially COMT inhibitors, while a high level of Akkermansia may be associated with aging.

Phylogenetic analysis and characterization of arsenic (As) transforming bacterial marker proteins following isolation of As-tolerant indigenous bacteria

Marker proteins play a significant role in bacterial arsenic (As) transformation. Phylogenetic analysis and three-dimensional (3D) characteristics of As transforming bacterial marker proteins guide the evolutionary origin and As transforming potential of the species. Indeed, As-tolerant bacteria also show a significant level of As transformation. Hence, characterization of As transforming bacterial marker proteins, isolation of As transforming bacteria, and proper integration of the findings may guide to elucidate how bacteria transform As. Therefore, phylogenetic analysis and 3D characterization of As transforming bacterial marker protein following isolation of potential indigenous As-tolerant indigenous bacteria were done to explore the mechanism of bacterial As transformation. Phylogenetic analysis of ten As transforming marker proteins (arsA, arsB, arsC, arsD, arsR, aioA, arrA, aioB, acr1, and acr3) in 20 potential bacterial genomes (except 19 for the acr3) were studied. Some bacterial genomes featured up to five marker proteins, and therefore, 3D characteristics of the marker proteins were analyzed in those genomes having three-to-five marker proteins. In phylogeny, species in close clades represent their phylogenetic resemblances and may have similar functions. P. aeruginosa, E. coli, and K. pneumonia were found to be more effective due to having the highest number (five) of marker proteins. In 3D protein modeling, most of the marker proteins were found to be active. Among 19 indigenous bacterial isolates, multiple isolates showed tolerance up to 50 mM As(III) and 250 mM As(V), which may potentially transform a significant quantities of As. Hence, integration of the results of phylogenetic analysis, 3D protein characteristics, and As tolerance in the bacterial isolates could guide to explore the mechanism of how bacteria transform As at cellular and molecular levels.

Relevance of Intestinal Microbiota in Immunoglobulin A Vasculitis With Abdominal Involvement

BACKGROUND

We explored the intestinal microbiota changes in IgAV with abdominal involvement (IgAV-GI) at the acute and convalescent stages and evaluated the role of intestinal microbiota in the clinical course of patients with IgAV.

METHODS

A total of 37 patients with IgAV were included, and the control group comprised 37 age- and sex-matched healthy children. Stool samples were collected from 28 children with IgAV-GI (19 in the acute stage and 9 in the recovery stage) and from nine children with non-abdominal involvement. Fecal specimens were selected and DNA was obtained using an extraction kit which was then subjected to high-throughput sequencing and analysis.

RESULTS

There was no significant difference in the community structure of the intestinal microbiota among the IgAV-GI acute, IgAV-GI convalescence, and IgAV-non-GI stages. The abundance of Veillonella in the acute stage of IgAV-GI was significantly higher than that in IgAV-non-GI and convalescence stages, and Ruminococcus was the most abundant in IgAV-GI convalescence. The α-diversity of children with IgAV was significantly lower than that of healthy children, and healthy children had higher intestinal microbiota richness and more evenly distributed species. In terms of changes in intestinal microbial diversity in patients with IgAV at the genus level, obligate anaerobes such as Bifidobacterium, Prevotella, Coprobacter, Prevotella_9, Blautia, Romboutsia, Parabacteroide, Subdoligranulum, and Roseburia were significantly reduced, and the enrichment of facultative anaerobe was represented by Bacteroides, Lachnoclostridium, and Alistipe.

CONCLUSION

Different bacterial species may be involved in the pathogenesis of different types of IgAV-GI. Differences were observed in the intestinal microbiota between healthy children and children with IgAV.

Spondylodiscitis due to anaerobic bacteria Veillonella parvula: Case report and literature review

Background:

While pyogenic spondylodiscitis due to Gram-positive aerobic bacteria and its treatment is well known, spondylodiscitis caused by anaerobic Gram-negative pathogen is rare. In particular, the spondylodiscitis caused by Veillonella species is an absolute rarity. Thus no established management recommendations exist.

Case Description:

A case report of a 79-year-old man with spondylodiscitis caused by Veillonella parvula with intramuscular abscess collection managed conservatively with stand-alone antibiotic therapy without a spinal stabilization procedure. A review of literature of all reported spondylodiscitis caused by Veillonella species was performed. After 3 week-intravenous therapy with the ceftriaxone in combination with the metronidazole followed by 3 weeks per oral therapy with amoxicillin/clavulanate, the complete recovery of the patient with the V. parvula infection was achieved.

Conclusion:

Treatment of the spondylodiscitis caused by Veillonella species should contain a beta-lactam with beta-lactamase inhibitor or third-generation cephalosporine. Six weeks of treatment seem to be sufficient for the complete recovery of the patient.

Disseminated Native Tricuspid Valve Infective Endocarditis and Vertebral Osteomyelitis Secondary to Veillonella dispar in a Patient Who Injects Drugs

We present the case of a 50-year-old man presenting with fever, back pain, persistent bacteremia with Veillonella dispar, echocardiographic evidence of a tricuspid valve vegetation increasing in size, and magnetic resonance imaging suggesting new vertebral osteomyelitis. He was successfully treated with intravenous ceftriaxone for six weeks. Deep-seated infections secondary to Veillonella species are rare, but cases of endocarditis, osteomyelitis, and meningitis have been reported in the literature. Given Veillonella species are normal human commensals present in the oropharyngeal flora, we suspect our patient developed native tricuspid valve endocarditis and vertebral osteomyelitis as a complication of either poor dentition or contaminated injection drug use paraphernalia and subsequent hematogenous seeding.

Epidural abscess and spondylitis caused by Veillonella parvula in a man on hemodialysis

Veillonella species rarely cause serious infections, but the incidence of infection has been increasing among immunocompromised individuals. This case of an epidural abscess and spondylitis caused by Veillonella parvula in a hemodialysis patient illustrates the importance of performing anaerobic blood culture in immunocompromised patients with signs of infection.

The gut microbiome in sickle cell disease: Characterization and potential implications

BACKGROUND

Sickle Cell Disease (SCD) is an inherited blood disorder that leads to hemolytic anemia, pain, organ damage and early mortality. It is characterized by polymerized deoxygenated hemoglobin, rigid sickle red blood cells and vaso-occlusive crises (VOC). Recurrent hypoxia-reperfusion injury in the gut of SCD patients could increase tissue injury, permeability, and bacterial translocation. In this context, the gut microbiome, a major player in health and disease, might have significant impact. This study sought to characterize the gut microbiome in SCD.

METHODS

Stool and saliva samples were collected from healthy controls (n = 14) and SCD subjects (n = 14). Stool samples were also collected from humanized SCD murine models including Berk, Townes and corresponding control mice. Amplified 16S rDNA was used for bacterial composition analysis using Next Generation Sequencing (NGS). Pairwise group analyses established differential bacterial groups at many taxonomy levels. Bacterial group abundance and differentials were established using DeSeq software.

RESULTS

A major dysbiosis was observed in SCD patients. The Firmicutes/Bacteroidetes ratio was lower in these patients. The following bacterial families were more abundant in SCD patients: Acetobacteraceae, Acidaminococcaceae, Candidatus Saccharibacteria, Peptostreptococcaceae, Bifidobacteriaceae, Veillonellaceae, Actinomycetaceae, Clostridiales, Bacteroidacbactereae and Fusobacteriaceae. This dysbiosis translated into 420 different operational taxonomic units (OTUs). Townes SCD mice also displayed gut microbiome dysbiosis as seen in human SCD.

CONCLUSION

A major dysbiosis was observed in SCD patients for bacteria that are known strong pro-inflammatory triggers. The Townes mouse showed dysbiosis as well and might serve as a good model to study gut microbiome modulation and its impact on SCD pathophysiology.

One or two membranes? Diderm Firmicutes challenge the Gram-positive/Gram-negative divide

How, when and why the transition between cell envelopes with one membrane (Gram-positives or monoderms) and two (Gram-negative or diderms) occurred in Bacteria is a key unanswered question in evolutionary biology. Different hypotheses have been put forward, suggesting that either the monoderm or the diderm phenotype is ancestral. The existence of diderm members in the classically monoderm Firmicutes challenges the Gram-positive/Gram-negative divide and provides a great opportunity to tackle the issue. In this review, we present current knowledge on the diversity of bacterial cell envelopes, including these atypical Firmicutes. We discuss how phylogenomic analysis supports the hypothesis that the diderm cell envelope architecture is an ancestral character in the Firmicutes, and that the monoderm phenotype in this phylum arose multiple times independently by loss of the outer membrane. Given the overwhelming distribution of diderm phenotypes with respect to monoderm ones, this scenario likely extends to the ancestor of all bacteria. Finally, we discuss the recent development of genetic tools for Veillonella parvula, a diderm Firmicute member of the human microbiome, which indicates it as an emerging new experimental model to investigate fundamental aspects of the diderm/monoderm transition.

Autotransporters Drive Biofilm Formation and Autoaggregation in the Diderm Firmicute Veillonella parvula

Veillonella parvula is an anaerobic commensal and opportunistic pathogen whose ability to adhere to surfaces or other bacteria and form biofilms is critical for it to inhabit complex human microbial communities such as the gut and oral microbiota. Although the adhesive capacity of V. parvula has been previously described, very little is known about the underlying molecular mechanisms due to a lack of genetically amenable Veillonella strains. In this study, we took advantage of a naturally transformable V. parvula isolate and newly adapted genetic tools to identify surface-exposed adhesins called autotransporters as the main molecular determinants of adhesion in this bacterium. This work therefore provides new insights on an important aspect of the V. parvula lifestyle, opening new possibilities for mechanistic studies of the contribution of biofilm formation to the biology of this major commensal of the oral-digestive tract.

The Negativicutes are a clade of the Firmicutes that have retained the ancestral diderm character and possess an outer membrane. One of the best studied Negativicutes, Veillonella parvula, is an anaerobic commensal and opportunistic pathogen inhabiting complex human microbial communities, including the gut and the dental plaque microbiota. Whereas the adhesion and biofilm capacities of V. parvula are expected to be crucial for its maintenance and development in these environments, studies of V. parvula adhesion have been hindered by the lack of efficient genetic tools to perform functional analyses in this bacterium. Here, we took advantage of a recently described naturally transformable V. parvula isolate, SKV38, and adapted tools developed for the closely related Clostridia spp. to perform random transposon and targeted mutagenesis to identify V. parvula genes involved in biofilm formation. We show that type V secreted autotransporters, typically found in diderm bacteria, are the main determinants of V. parvula autoaggregation and biofilm formation and compete with each other for binding either to cells or to surfaces, with strong consequences for V. parvula biofilm formation capacity. The identified trimeric autotransporters have an original structure compared to classical autotransporters identified in Proteobacteria, with an additional C-terminal domain. We also show that inactivation of the gene coding for a poorly characterized metal-dependent phosphohydrolase HD domain protein conserved in the Firmicutes and their closely related diderm phyla inhibits autotransporter-mediated biofilm formation. This study paves the way for further molecular characterization of V. parvula interactions with other bacteria and the host within complex microbiota environments.

IMPORTANCEVeillonella parvula is an anaerobic commensal and opportunistic pathogen whose ability to adhere to surfaces or other bacteria and form biofilms is critical for it to inhabit complex human microbial communities such as the gut and oral microbiota. Although the adhesive capacity of V. parvula has been previously described, very little is known about the underlying molecular mechanisms due to a lack of genetically amenable Veillonella strains. In this study, we took advantage of a naturally transformable V. parvula isolate and newly adapted genetic tools to identify surface-exposed adhesins called autotransporters as the main molecular determinants of adhesion in this bacterium. This work therefore provides new insights on an important aspect of the V. parvula lifestyle, opening new possibilities for mechanistic studies of the contribution of biofilm formation to the biology of this major commensal of the oral-digestive tract.

Acromioclavicular Septic Arthritis Caused by Veillonella parvula

We hereby report the case of a primary acromioclavicular septic arthritis caused by Veillonella parvula. This bacteria is rare as a pathogen but is well known as a commensal of the lungs, vagina, mouth, and gastrointestinal tract of humans. However, it may turn as an opportunistic pathogen. It was isolated in blood culture and confirmed in biopsy specimen. The patient had complete recovery after surgical washout with second look at postoperative day two and targeted antibiotic treatment.

Multidrug resistance in anaerobes

Multidrug resistance (MDR) in anaerobes is not a well-known topic. Bacteroides fragilis group isolates have numerous resistance determinants such as multidrug efflux pumps, cfiA and nimB genes and activating insertion sequences, and some isolates exhibited extensive drug-resistant patterns. MDR rates in B. fragilis group were from 1.5 to >18% and up to >71% in cfiA and nimB positive isolates carrying insertion sequences. MDR was present in >1/2 of Clostridioides difficile isolates, most often in epidemic/hypervirulent strains and unusually high metronidazole or vancomycin resistance has been reported in single studies. MDR was found in Prevotella spp. (in ≤10% of isolates), Finegoldia magna, Veillonella spp. and Cutibacterium acnes. Resistance in the anaerobes tends to be less predictable and anaerobic microbiology is required in more laboratories. New hopes may be new antibiotics such as eravacycline, cadazolid, surotomycin, ridinilazol or C. difficile toxoid vaccines; however, more efforts are needed to track the MDR in anaerobes.

Lytic lesions: looking lethal but leaving room for a simple cure? A case of Veillonella spinal osteomyelitis

Introduction. Diagnosing clinically significant infection caused by Veillonella species can be a challenge. Veillonella species are usually found in polymicrobial processes and are often regarded as a contaminant. Additionally, they are slow to grow in culture and this can lead to a delay in diagnosis or a missed diagnosis. Veillonella species rarely cause serious infections, but have been found to cause bacteraemia and osteomyelitis.

Case presentation. A 67-year-old man with a history of treated prostate cancer presented with 2 weeks of progressive lower back pain and weakness. He had no signs or symptoms of active infection. He was found to have multiple lytic lesions in his lumbar spine that were initially suspected to be secondary to metastatic cancer. However, tissue and blood cultures were ultimately consistent with infection by Veillonella species.

Conclusion. This case report highlights the fact that uncommon illnesses can often present like common disease processes. Because of the radiological appearance of the patient’s lesions and his lack of infectious symptoms, a diagnosis of metastatic cancer was initially thought to be likely. Relying on the pathology and culture data, and waiting on the initiation of antimicrobials until the diagnosis was accurately established, were important factors in diagnosing and treating this infection. Veillonella species can be true pathogens when found in isolation and associated with bacteraemia. Additionally, they can cause an indolent infection that can lead to osteomyelitis. Failure to accurately diagnose this infection in a timely manner would have led to ongoing debility and diagnostic uncertainty for this patient.

Outer Membrane Proteome of Veillonella parvula: A Diderm Firmicute of the Human Microbiome

Veillonella parvula is a biofilm-forming commensal found in the lungs, vagina, mouth, and gastro-intestinal tract of humans, yet it may develop into an opportunistic pathogen. Furthermore, the presence of Veillonella has been associated with the development of a healthy immune system in infants. Veillonella belongs to the Negativicutes, a diverse clade of bacteria that represent an evolutionary enigma: they phylogenetically belong to Gram-positive (monoderm) Firmicutes yet maintain an outer membrane (OM) with lipopolysaccharide similar to classic Gram-negative (diderm) bacteria. The OMs of Negativicutes have unique characteristics including the replacement of Braun's lipoprotein by OmpM for tethering the OM to the peptidoglycan. Through phylogenomic analysis, we have recently provided bioinformatic annotation of the Negativicutes diderm cell envelope. We showed that it is a unique type of envelope that was present in the ancestor of present-day Firmicutes and lost multiple times independently in this phylum, giving rise to the monoderm architecture; however, little experimental data is presently available for any Negativicutes cell envelope. Here, we performed the first experimental proteomic characterization of the cell envelope of a diderm Firmicute, producing an OM proteome of V. parvula. We initially conducted a thorough bioinformatics analysis of all 1,844 predicted proteins from V. parvula DSM 2008's genome using 12 different localization prediction programs. These results were complemented by protein extraction with surface exposed (SE) protein tags and by subcellular fractionation, both of which were analyzed by liquid chromatography tandem mass spectrometry. The merging of proteomics and bioinformatics results allowed identification of 78 OM proteins. These include a number of receptors for TonB-dependent transport, the main component of the BAM system for OM protein biogenesis (BamA), the Lpt system component LptD, which is responsible for insertion of LPS into the OM, and several copies of the major OmpM protein. The annotation of V. parvula's OM proteome markedly extends previous inferences on the nature of the cell envelope of Negativicutes, including the experimental evidence of a BAM/TAM system for OM protein biogenesis and of a complete Lpt system for LPS transport to the OM. It also provides important information on the role of OM components in the lifestyle of Veillonella, such as a possible gene cluster for O-antigen synthesis and a large number of adhesins. Finally, many OM hypothetical proteins were identified, which are priority targets for further characterization.

Phylogenomic analysis supports the ancestral presence of LPS-outer membranes in the Firmicutes

One of the major unanswered questions in evolutionary biology is when and how the transition between diderm (two membranes) and monoderm (one membrane) cell envelopes occurred in Bacteria. The Negativicutes and the Halanaerobiales belong to the classically monoderm Firmicutes, but possess outer membranes with lipopolysaccharide (LPS-OM). Here, we show that they form two phylogenetically distinct lineages, each close to different monoderm relatives. In contrast, their core LPS biosynthesis enzymes were inherited vertically, as in the majority of bacterial phyla. Finally, annotation of key OM systems in the Halanaerobiales and the Negativicutes shows a puzzling combination of monoderm and diderm features. Together, these results support the hypothesis that the LPS-OMs of Negativicutes and Halanaerobiales are remnants of an ancient diderm cell envelope that was present in the ancestor of the Firmicutes, and that the monoderm phenotype in this phylum is a derived character that arose multiple times independently through OM loss.

DOI:http://dx.doi.org/10.7554/eLife.14589.001

The cell envelope is one of the evolutionarily oldest parts of a bacterium. This structure – made up of a cell wall and either one or two cell membranes – surrounds the bacterial cell, maintaining the cell’s structure and providing an interface through which bacteria can sense their environment and communicate.

Bacteria can be broadly classed based on the number of cell membranes that their envelope consists of. Bacteria that have a single cell membrane are known as “monoderm”, whereas those with two membranes are termed “diderm”. The number of membranes that bacteria have can affect how well they resist antibacterial compounds. When, how and why bacteria switched between monoderm and diderm cell envelopes are some of the major unanswered questions in evolutionary biology.

The textbook example of a monoderm cell envelope can be found in bacteria called Firmicutes. This group includes some notoriously harmful bacteria such as Staphylococcus, which can cause conditions ranging from abscesses to pneumonia. However, some Firmicutes possess two cell membranes. It was unclear how these unusual diderm Firmicutes developed a second membrane, and how they are related to their monoderm relatives.

Antunes, Poppleton et al. set out to answer these questions by analyzing the information contained in the thousands of bacterial genomes that have already been described. The results indicate that Firmicutes originally had diderm envelopes, and that species with monoderm envelopes arose independently several times through the loss of their outermost membrane.

Future work is needed to investigate the driving forces and the precise mechanism that led most Firmicutes to lose their outer membrane. Also, further characterization of diderm Firmicutes will provide key information about the biology of these poorly understood bacteria.

DOI:http://dx.doi.org/10.7554/eLife.14589.002