Cryo-Electron Tomography Reveals the Complex Ultrastructural Organization of Multicellular Filamentous Chloroflexota (Chloroflexi) Bacteria

Gaisin, Vasil A.; Kooger, Romain; Grouzdev, Denis S.; Горленко, В. М.; Pilhofer, Martin

doi:10.3389/fmicb.2020.01373

Cited by 26 publications

(20 citation statements)

References 88 publications

(148 reference statements)

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“…All Bacilli and most Clostridia are monoderms with a thick peptidoglycan, but some Clostridia [ 84 ] (Halanaerobiales and Thermoanaerobacteriales) and the Negativicutes have two membranes (some with lipopolysaccharides in the outer membrane) and a relatively thin peptidoglycan layer [ 16 , 85 , 86 ]. Regarding the status of the Chloroflexi cell-wall architecture, it is still controversial [ 68 , 87 , 88 ]. Beside these canonical diderm and monoderm phyla, respectively corresponding to classical Gram- and Gram+ bacteria, there exist a series of organisms with atypical cell-wall architectures.…”

Section: Resultsmentioning

confidence: 99%

“…Pattern 2 shows that Chloroflexi share the same gene distribution as monoderm Terrabacteria, despite being mostly considered as diderms (3 out of 4 genomes) in our reconstruction of the cell wall. Currently, there is still debate on whether Chloroflexi are monoderm or diderm organisms, microscopical observations having been inconclusive so far but hinting at the presence of an outer membrane in some Chloroflexi [ 87 , 88 ]. The fact that they share the same outer membrane gene distribution pattern as monoderm Terrabacteria is a clue in favour of Chloroflexi having only one membrane too.…”

Section: Discussionmentioning

confidence: 99%

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Was the Last Bacterial Common Ancestor a Monoderm after All?

Léonard

Sauvage

Lupo

et al. 2022

Genes

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The very nature of the last bacterial common ancestor (LBCA), in particular the characteristics of its cell wall, is a critical issue to understand the evolution of life on earth. Although knowledge of the relationships between bacterial phyla has made progress with the advent of phylogenomics, many questions remain, including on the appearance or disappearance of the outer membrane of diderm bacteria (also called Gram-negative bacteria). The phylogenetic transition between monoderm (Gram-positive bacteria) and diderm bacteria, and the associated peptidoglycan expansion or reduction, requires clarification. Herein, using a phylogenomic tree of cultivated and characterized bacteria as an evolutionary framework and a literature review of their cell-wall characteristics, we used Bayesian ancestral state reconstruction to infer the cell-wall architecture of the LBCA. With the same phylogenomic tree, we further revisited the evolution of the division and cell-wall synthesis (dcw) gene cluster using homology- and model-based methods. Finally, extensive similarity searches were carried out to determine the phylogenetic distribution of the genes involved with the biosynthesis of the outer membrane in diderm bacteria. Quite unexpectedly, our analyses suggest that all cultivated and characterized bacteria might have evolved from a common ancestor with a monoderm cell-wall architecture. If true, this would indicate that the appearance of the outer membrane was not a unique event and that selective forces have led to the repeated adoption of such an architecture. Due to the lack of phenotypic information, our methodology cannot be applied to all extant bacteria. Consequently, our conclusion might change once enough information is made available to allow the use of an even more diverse organism selection.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Was the Last Bacterial Common Ancestor a Monoderm after All?

Léonard

Sauvage

Lupo

et al. 2022

Genes

View full text Add to dashboard Cite

show abstract

“…Two breakthrough works recently appeared enlarge the knowledge of Chloroflexus aggregans and help in better positioning it in the evolutionary scale toward the appearance of photosynthetic organisms (particularly cyanobacteria, also capable of habitat adaptation and considered the ancestors of chloroplasts). The recent descriptions of its cellular ultrastructure [ 38 ] and transcription pathways related to energy metabolism [ 39 ] highlighted astonishing morphological traits, such as a cytoplasm crowded with proto-organelles, and cycling growth modes relying on a noticeable metabolic plasticity. Likewise, it is expected that the enzymatic equipment of this organism could reveal new, interesting and original functionalities that are worthwhile to be investigated.…”

Section: Discussionmentioning

confidence: 99%

A New Thermophilic Ene-Reductase from the Filamentous Anoxygenic Phototrophic Bacterium Chloroflexus aggregans

et al. 2021

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Aiming at expanding the biocatalytic toolbox of ene-reductase enzymes, we decided to explore photosynthetic extremophile microorganisms as unique reservoir of (new) biocatalytic activities. We selected a new thermophilic ene-reductase homologue in Chloroflexus aggregans, a peculiar filamentous bacterium. We report here on the functional and structural characterization of this new enzyme, which we called CaOYE. Produced in high yields in recombinant form, it proved to be a robust biocatalyst showing high thermostability, good solvent tolerance and a wide range of pH optimum. In a preliminary screening, CaOYE displayed a restricted substrate spectrum (with generally lower activities compared to other ene-reductases); however, given the amazing metabolic ductility and versatility of Chloroflexus aggregans, further investigations could pinpoint peculiar chemical activities. X-ray crystal structure has been determined, revealing conserved features of Class III (or thermophilic-like group) of the family of Old Yellow Enzymes: in the crystal packing, the enzyme was found to assemble as dimer even if it behaves as a monomer in solution. The description of CaOYE catalytic properties and crystal structure provides new details useful for enlarging knowledge, development and application of this class of enzymes.

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“…Moreover, their presence/absence may be used to infer a diderm or monoderm phenotype in the vast majority of phyla for which cell envelope characterization is missing. For example, the absence of OmpM from the Chloroflexi suggests that the diderm-like envelopes recently observed in members of this phylum may actually be other types of structures (Gaisin et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

An ancient divide in outer membrane tethering systems in Bacteria

Witwinowski

Sartori-Rupp

Taïb

et al. 2021

Preprint

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Recent data support the hypothesis that Gram-positive bacteria (monoderms) arose from Gram-negatives (diderms) through loss of the outer membrane (OM). However how this happened remains unknown. Considering that tethering of the OM is essential for cell envelope stability in diderm bacteria we hypothesize that its destabilization may have been involved in OM loss. Here, we present an in-depth analysis of the four main OM tethering systems across all Bacteria. We show that their distribution strikingly follows the bacterial phylogeny with a bimodal distribution matching the deepest phylogenetic cleavage between Terrabacteria (a clade encompassing Cyanobacteria, Deinococcus/Thermus, Firmicutes, etc.) and Gracilicutes (a clade encompassing Proteobacteria, Bacteroidetes, Spirochaetes, etc.). Diderm Terrabacteria display as the main system OmpM, a porin that attaches non-covalently to modified peptidoglycan or to secondary cell wall polymers. In contrast, the lipoprotein Pal is restricted to the Gracilicutes along with a more sporadic occurrence of OmpA. While Braun's lipoprotein Lpp is largely considered as the textbook example of OM attachment, it is actually present only in a subclade of Gammaproteobacteria. We propose an evolutionary scenario whereby the last common bacterial ancestor used a system based on OmpM, which was later replaced by one based on the lipoprotein Pal concomitantly to the emergence of the Lol machinery to address lipoproteins to the OM, with OmpA as a possible transition state. We speculate that the existence of only one main OM tethering system in the Terrabacteria would have allowed the multiple emergences of the monoderm phenotype specifically observed in this clade through OmpM perturbation. We test this hypothesis by inactivating all four ompM gene copies in the genetically tractable diderm Firmicute Veillonella parvula. The resulting mutant is severely affected in growth and displays high sensitivity to OM stress. High resolution imaging and tomogram reconstructions reveal a dramatic - yet non-lethal - phenotype, in which vast portions of the OM detach, producing large vesicles surrounding multiple monoderm-like cells sharing a common periplasm. Complementation by a single OmpM rescues the phenotype to a normal cell envelope. Together, our results highlight an ancient shift in bacterial evolution involving OM tethering systems. They suggest a possible mechanism for OM loss and a high flexibility of the cell envelope in diderm Firmicutes, making them ideal models to further refine our understanding of the mechanisms involved in bacterial OM stability, and opening the way to recapitulate the monoderm/diderm transition in the laboratory.

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Cryo-Electron Tomography Reveals the Complex Ultrastructural Organization of Multicellular Filamentous Chloroflexota (Chloroflexi) Bacteria

Cited by 26 publications

References 88 publications

Was the Last Bacterial Common Ancestor a Monoderm after All?

Was the Last Bacterial Common Ancestor a Monoderm after All?

A New Thermophilic Ene-Reductase from the Filamentous Anoxygenic Phototrophic Bacterium Chloroflexus aggregans

An ancient divide in outer membrane tethering systems in Bacteria

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