An ethanolamine-phosphate modified glycolipid in Clostridium acetobutylicum that responds to membrane stress

A Membrane Biophysics Perspective on the Mechanism of Alcohol Toxicity

Motivations for understanding the underlying mechanisms of alcohol toxicity range from economical to toxicological and clinical. On the one hand, acute alcohol toxicity limits biofuel yields, and on the other hand, acute alcohol toxicity provides a vital defense mechanism to prevent the spread of disease. Herein the role that stored curvature elastic energy (SCE) in biological membranes might play in alcohol toxicity is discussed, for both short and long-chain alcohols. Structure-toxicity relationships for alcohols ranging from methanol to hexadecanol are collated, and estimates of alcohol toxicity per alcohol molecule in the cell membrane are made. The latter reveal a minimum toxicity value per molecule around butanol before alcohol toxicity per molecule increases to a maximum around decanol and subsequently decreases again. The impact of alcohol molecules on the lamellar to inverse hexagonal phase transition temperature (T_H) is then presented and used as a metric to assess the impact of alcohol molecules on SCE. This approach suggests the nonmonotonic relationship between alcohol toxicity and chain length is consistent with SCE being a target of alcohol toxicity. Finally, in vivo evidence for SCE-driven adaptations to alcohol toxicity in the literature are discussed.

Lipid diversity in clostridia

Studies of the lipidomes of twenty-one species of clostridia have revealed considerable diversity. Even among those species now defined as Clostridium sensu stricto, which are related to Clostridium butyricum, the type species, lipid analysis has shown that a number of distinct clades have characteristic polar lipids. All species of Clostridium sensu stricto have phosphatidylethanolamine, phosphatidylglycerol and cardiolipin which are present as all acyl or alk-1'-enyl acyl (plasmalogen) species. In addition, almost every clade has specialized polar lipids. For example, the group closely related to Clostridium beijerinckii and several other solventogenic species has glycerol acetals of plasmenylethanolamine, which protects the membrane bilayer arrangement when the lipids are highly unsaturated or in the presence of solvents. The group related to Clostridium novyi has aminoacyl-phosphatidylglycerol, which protects these pathogens from cationic antimicrobial peptides (CAMPs) of innate immunity. Clostridium botulinum species, which fall into several groups, align with these clades, and have the same specific lipids. This review will present the current state of knowledge on clostridial lipids.

Life without air

An early exposure to lipid biochemistry in the laboratory of Konrad Bloch resulted in a fascination with the biosynthesis, structures, and functions of bacterial lipids. The discovery of plasmalogens (1-alk-1'-enyl, 2-acyl phospholipids) in anaerobic Gram-positive bacteria led to studies on the physical chemistry of these lipids and the cellular regulation of membrane lipid polymorphism in bacteria. Later studies in several laboratories showed that the formation of the alk-1-enyl ether bond involves an aerobic process in animal cells and thus is fundamentally different from that in anaerobic organisms. Our work provides evidence for an anaerobic process in which plasmalogens are formed from their corresponding diacyl lipids. Studies on the roles of phospholipases in Listeria monocytogenes revealed distinctions between its phospholipases and those previously discovered in other bacteria and showed how the Listeria enzymes are uniquely fitted to the intracellular lifestyle of this significant human pathogen.

Lipidomic Analysis of Clostridium cadaveris and Clostridium fallax

The lipidomes of Clostridium fallax and Clostridium cadaveris were studied using thin-layer chromatography (TLC) and normal phase liquid chromatography/mass spectrometry (NPLC/MS). Both species contain diradylglycerol (DRG), monohexosyldiradylglycerol (MHDRG), monohexosyl monoacylglycerol (MHMAG), phosphatidylglycerol (PtdGro), and phosphatidylethanolamine (PtdEtn). DRG, MHDRG, PtdEtn, and PtdGro are present in both diacyl and alk-1-enyl acyl (plasmalogen) forms. Both species contain cardiolipin (Ptd2 Gro), which is present in tetraacyl, monoalkenyl-triacyl, and dialkenyl-diacyl forms. Both species contain small amounts of phosphatidylcholine (PtdCho). The presence of octadecadienoic (18:2) acyl chains in some PtdCho species indicates that they arise from the medium because no 18:2 is seen in the other lipids and clostridia generally lack the capacity to synthesize polyunsaturated fatty acids. The major lipidomic differences between these two species are that C. fallax contains a glycerolacetal of plasmenylethanolamine while C. cadaveris contains an ethanolamine-phosphate-modified diacylglycerol. The significance of these lipid compositions is discussed.

Major roles for minor bacterial lipids identified by mass spectrometry

Mass spectrometry of lipids, especially those isolated from bacteria, has ballooned over the past two decades, affirming in the process the complexity of the lipidome. With this has come the identification of new and interesting lipid structures. Here is an overview of several novel lipids, from both Gram-negative and Gram-positive bacteria with roles in health and disease, whose structural identification was facilitated using mass spectrometry. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.

Engineering membrane and cell-wall programs for tolerance to toxic chemicals: Beyond solo genes

Metabolite toxicity in microbes, particularly at the membrane, remains a bottleneck in the production of fuels and chemicals. Under chemical stress, native adaptation mechanisms combat hyper-fluidization by modifying the phospholipids in the membrane. Recent work in fluxomics reveals the mechanism of how membrane damage negatively affects energy metabolism while lipidomic and transcriptomic analyses show that strains evolved to be tolerant maintain membrane fluidity under stress through a variety of mechanisms such as incorporation of cyclopropanated fatty acids, trans-unsaturated fatty acids, and upregulation of cell wall biosynthesis genes. Engineered strains with modifications made in the biosynthesis of fatty acids, peptidoglycan, and lipopolysaccharide have shown increased tolerance to exogenous stress as well as increased production of desired metabolites of industrial importance. We review recent advances in elucidation of mechanisms or toxicity and tolerance as well as efforts to engineer the bacterial membrane and cell wall.

The cellular lipids of Romboutsia

We have examined the lipids of three isolates, Romboutsia lituseburensis, Romboutsia ilealis, and Romboutsia sp. strain FRIFI, of the newly described genus Romboutsia by two-dimensional thin-layer chromatography (2D-TLC) and by liquid chromatography/mass spectrometry (LC/MS). We have found three phospholipids, phosphatidylglycerol (PG), cardiolipin and phosphatidic acid in all three species. A fourth phospholipid, lysyl-PG, was found in R. lituseburensis and strain FRIFI. Polyprenyl-phosphates were identified in the lipid extracts of all three species. Three glycolipids, mono-, di- and tri-hexosyldiacylglycerol, were common to all three species. An additional glycolipid, tetrahexosyl-diacylglycerol was identified in strain FRIFI. Acylated trihexosyldiacylglycerol and acyl-tetrahexosydiacylglycerol were also found in R. ilealis and strain FRIFI. Remarkably, no alk-1-enyl ether lipids (plasmalogens) were present in Romboutsia as distinct from bacteria of the related genus Clostridium in which these ether lipids are common. We have compared the lipidome of Romboutsia with that recently described for Clostridium difficile, which has plasmalogens, no lysyl-PG, and no tetrahexosyl-diacylglycerol. According to 16S rRNA gene sequencing, Romboutsia spp. and C. difficile are closely related (>95% sequence identity).

Changes in membrane plasmalogens of Clostridium pasteurianum during butanol fermentation as determined by lipidomic analysis

Changes in membrane lipid composition of Clostridium pasteurianum NRRL B-598 were studied during butanol fermentation by lipidomic analysis, performed by high resolution electrospray ionization tandem mass spectrometry. The highest content of plasmalogen phospholipids correlated with the highest butanol productivity, which indicated a probable role of these compounds in the complex responses of cells toward butanol stress. A difference in the ratio of saturated to unsaturated fatty acids was found between the effect of butanol produced by the cells and butanol added to the medium. A decrease in the proportion of saturated fatty acids during conventional butanol production was observed while a rise in the content of these acids appeared when butanol was added to the culture. The largest change in total plasmalogen content was observed one hour after butanol addition i.e. at the 7th hour of cultivation. When butanol is produced by bacterial cells, then the cells are not subjected to severe stress and responded to it by relatively slowly changing the content of fatty acids and plasmalogens, while after a pulse addition of external butanol (to a final non-lethal concentration of 0.5 % v/v) the cells reacted relatively quickly (within a time span of tens of minutes) by increasing the total plasmalogen content.

Characterization of Romboutsia ilealis gen. nov., sp. nov., isolated from the gastro-intestinal tract of a rat, and proposal for the reclassification of five closely related members of the genus Clostridium into the genera Romboutsia gen. nov., Intestinibacter gen. nov., Terrisporobacter gen. nov. and Asaccharospora gen. nov

A Gram-positive staining, rod-shaped, non-motile, spore-forming obligately anaerobic bacterium, designated CRIBT, was isolated from the gastro-intestinal tract of a rat and characterized. The major cellular fatty acids of strain CRIBT were saturated and unsaturated straight-chain C12-C19 fatty acids, with C16:0 being the predominant fatty acid. The polar lipid profile comprised six glycolipids, four phospholipids and one lipid that did not stain with any of the specific spray reagents used. The only quinone was MK-6. The predominating cell-wall sugars were glucose and galactose. The peptidoglycan type of strain CRIBT was A1σ lanthionine-direct. The genomic DNA G+C content of strain CRIBT was 28.1 mol%. On the basis of 16S rRNA gene sequence similarity, strain CRIBT was most closely related to a number of species of the genus Clostridium, including Clostridium lituseburense (97.2%), Clostridium glycolicum (96.2%), Clostridium mayombei (96.2%), Clostridium bartlettii (96.0%) and Clostridium irregulare (95.5%). All these species show very low 16S rRNA gene sequence similarity (<85%) to the type strain of Clostridium butyricum, the type species of the genus Clostridium. DNA-DNA hybridization with closely related reference strains indicated reassociation values below 32%. On the basis of phenotypic and genetic studies, a novel genus, Romboutsia gen. nov., is proposed. The novel isolate CRIBT (=DSM 25109T=NIZO 4048T) is proposed as the type strain of the type species, Romboutsia ilealis gen. nov., sp. nov., of the proposed novel genus. It is proposed that C. lituseburense is transferred to this genus as Romboutsia lituseburensis comb. nov. Furthermore, the reclassification into novel genera is proposed for C. bartlettii, as Intestinibacter bartlettii gen. nov., comb. nov. (type species of the genus), C. glycolicum, as Terrisporobacter glycolicus gen. nov., comb. nov. (type species of the genus), C. mayombei, as Terrisporobacter mayombei gen. nov., comb. nov., and C. irregulare, as Asaccharospora irregularis gen. nov., comb. nov. (type species of the genus), on the basis of additional data collected in this study. In addition, an emendation of the species Peptostreptococcus anaerobius and the order Eubacteriales is provided.