Microbial Cell Wall

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Molecular Microbiology and Immunology".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 15576

Special Issue Editors

1. Department of Chemistry, School of Science, Osaka University, 1-1 Osaka University Machikaneyama, Toyonaka, Osaka 560-0043, Japan
2. Department of Chemical Sciences, University of Napoli Federico II, Complesso Universitario Monte Santangelo, Via Cintia 4, I-80126 Napoli, Italy
Interests: innate immunity; bacterial cell wall; Lipopolysaccharides; peptidoglycan; microbial glycobiology
Special Issues, Collections and Topics in MDPI journals
Department of Chemical Sciences, University of Naples Federico II, Naples, Italy
Interests: lipopolysaccharides; innate immunity; bacterial glycans; structural characterization; microbial glycobiology; mass spectrometry; NMR
Department of Chemical Sciences, University of Naples Federico II, Naples, Italy
Interests: giant viruses; N-glycosylation; glycans analysis; isolation and purification of glycans

Special Issue Information

Dear Colleagues,

The majority of microorganisms own an external envelope that is not just an inert covering but an essential structural component that must be sufficiently stable against threats from the environment to protect and give shape to the microbe while playing multiple roles in interactions with host cells. The location of cell envelopes and their chemical peculiarity makes them an attractive candidate for developing vaccines against microbial diseases, including drug-resistant pathogens. Therefore, ranging from bacteria to archaea and viruses, the concept of a “microbial envelope”, in sensu lato, is surely a fascinating and astounding area of research.

The origin and complexity of cell envelopes still represent an enigma in biology. Widely investigated, the cell envelope in bacteria consists of a cell wall with either one (mono-derm) or two (diderm) membranes. In contrast, most aspects of the biosynthesis and structure of the archaeal cell envelope, which presents several unique characteristics, have not been adequately characterized. Even more singular is the viral envelope, which is considered (when present) as a fusion machine that allows viral entry into host cells. Indeed, the scattered occurrence of envelopes among viral taxa suggests that they have evolved convergently, depending on the target hosts.

Given these premises, the aim of this Special Issue is to collect papers focused on deciphering the physiology, genetics, immunology, and chemistry of microbial envelopes to improve the knowledge in this field, which is crucial to appreciate their significance with regard to the microbiology and immunology of microbes.

Prof. Antonio Molinaro
Dr. Flaviana Di Lorenzo
Dr. Immacolata Speciale
Guest Editors

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Keywords

  • microbial envelope
  • cell wall
  • bacteria
  • archaea
  • viruses
  • physiology
  • genetics
  • immunology
  • chemistry

Published Papers (5 papers)

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Research

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18 pages, 1514 KiB  
Article
The Unusual Lipid A Structure and Immunoinhibitory Activity of LPS from Marine Bacteria Echinicola pacifica KMM 6172T and Echinicola vietnamensis KMM 6221T
Microorganisms 2021, 9(12), 2552; https://doi.org/10.3390/microorganisms9122552 - 10 Dec 2021
Cited by 5 | Viewed by 2300
Abstract
Gram-negative bacteria experiencing marine habitats are constantly exposed to stressful conditions dictating their survival and proliferation. In response to these selective pressures, marine microorganisms adapt their membrane system to ensure protection and dynamicity in order to face the highly mutable sea environments. As [...] Read more.
Gram-negative bacteria experiencing marine habitats are constantly exposed to stressful conditions dictating their survival and proliferation. In response to these selective pressures, marine microorganisms adapt their membrane system to ensure protection and dynamicity in order to face the highly mutable sea environments. As an integral part of the Gram-negative outer membrane, structural modifications are commonly observed in the lipopolysaccharide (LPS) molecule; these mainly involve its glycolipid portion, i.e., the lipid A, mostly with regard to fatty acid content, to counterbalance the alterations caused by chemical and physical agents. As a consequence, unusual structural chemical features are frequently encountered in the lipid A of marine bacteria. By a combination of data attained from chemical, MALDI-TOF mass spectrometry (MS), and MS/MS analyses, here, we describe the structural characterization of the lipid A isolated from two marine bacteria of the Echinicola genus, i.e., E. pacifica KMM 6172T and E. vietnamensis KMM 6221T. This study showed for both strains a complex blend of mono-phosphorylated tri- and tetra-acylated lipid A species carrying an additional sugar moiety, a d-galacturonic acid, on the glucosamine backbone. The unusual chemical structures are reflected in a molecule that only scantly activates the immune response upon its binding to the LPS innate immunity receptor, the TLR4-MD-2 complex. Strikingly, both LPS potently inhibited the toxic effects of proinflammatory Salmonella LPS on human TLR4/MD-2. Full article
(This article belongs to the Special Issue Microbial Cell Wall)
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15 pages, 943 KiB  
Article
A Differential Proteomic Approach to Characterize the Cell Wall Adaptive Response to CO2 Overpressure during Sparkling Wine-Making Process
Microorganisms 2020, 8(8), 1188; https://doi.org/10.3390/microorganisms8081188 - 04 Aug 2020
Viewed by 2483
Abstract
In this study, a first proteomic approach was carried out to characterize the adaptive response of cell wall-related proteins to endogenous CO2 overpressure, which is typical of second fermentation conditions, in two wine Saccharomyces cerevisiae strains (P29, a conventional second fermentation strain, [...] Read more.
In this study, a first proteomic approach was carried out to characterize the adaptive response of cell wall-related proteins to endogenous CO2 overpressure, which is typical of second fermentation conditions, in two wine Saccharomyces cerevisiae strains (P29, a conventional second fermentation strain, and G1, a flor yeast strain implicated in sherry wine making). The results showed a high number of cell wall proteins in flor yeast G1 under pressure, highlighting content at the first month of aging. The cell wall proteomic response to pressure in flor yeast G1 was characterized by an increase in both the number and content of cell wall proteins involved in glucan remodeling and mannoproteins. On the other hand, cell wall proteins responsible for glucan assembly, cell adhesion, and lipid metabolism stood out in P29. Over-represented proteins under pressure were involved in cell wall integrity (Ecm33p and Pst1p), protein folding (Ssa1p and Ssa2p), and glucan remodeling (Exg2p and Scw4p). Flocculation-related proteins were not identified under pressure conditions. The use of flor yeasts for sparkling wine elaboration and improvement is proposed. Further research based on the genetic engineering of wine yeast using those genes from protein biomarkers under pressure alongside the second fermentation in bottle is required to achieve improvements. Full article
(This article belongs to the Special Issue Microbial Cell Wall)
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21 pages, 5963 KiB  
Article
Overexpression of lpxT Gene in Escherichia coli Inhibits Cell Division and Causes Envelope Defects without Changing the Overall Phosphorylation Level of Lipid A
Microorganisms 2020, 8(6), 826; https://doi.org/10.3390/microorganisms8060826 - 30 May 2020
Cited by 4 | Viewed by 3171
Abstract
LpxT is an inner membrane protein that transfers a phosphate group from the essential lipid undecaprenyl pyrophosphate (C-55PP) to the lipid A moiety of lipopolysaccharide, generating a lipid A tris-phosphorylated species. The protein is encoded by the non-essential lpxT gene, which is [...] Read more.
LpxT is an inner membrane protein that transfers a phosphate group from the essential lipid undecaprenyl pyrophosphate (C-55PP) to the lipid A moiety of lipopolysaccharide, generating a lipid A tris-phosphorylated species. The protein is encoded by the non-essential lpxT gene, which is conserved in distantly related Gram-negative bacteria. In this work, we investigated the phenotypic effect of lpxT ectopic expression from a plasmid in Escherichia coli. We found that lpxT induction inhibited cell division and led to the formation of elongated cells, mostly with absent or altered septa. Moreover, the cells became sensitive to detergents and to hypo-osmotic shock, indicating that they had cell envelope defects. These effects were not due to lipid A hyperphosphorylation or C-55PP sequestering, but most likely to defective lipopolysaccharide transport. Indeed, lpxT overexpression in mutants lacking the L,D-transpeptidase LdtD and LdtE, which protect cells with outer membrane defects from osmotic lysis, caused cell envelope defects. Moreover, we found that pyrophosphorylated lipid A was also produced in a lpxT deletion mutant, indicating that LpxT is not the only protein able to perform such lipid A modification in E. coli. Full article
(This article belongs to the Special Issue Microbial Cell Wall)
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Review

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27 pages, 2582 KiB  
Review
Molecular Mechanisms Involved in the Multicellular Growth of Ustilaginomycetes
Microorganisms 2020, 8(7), 1072; https://doi.org/10.3390/microorganisms8071072 - 18 Jul 2020
Cited by 9 | Viewed by 3639
Abstract
Multicellularity is defined as the developmental process by which unicellular organisms became pluricellular during the evolution of complex organisms on Earth. This process requires the convergence of genetic, ecological, and environmental factors. In fungi, mycelial and pseudomycelium growth, snowflake phenotype (where daughter cells [...] Read more.
Multicellularity is defined as the developmental process by which unicellular organisms became pluricellular during the evolution of complex organisms on Earth. This process requires the convergence of genetic, ecological, and environmental factors. In fungi, mycelial and pseudomycelium growth, snowflake phenotype (where daughter cells remain attached to their stem cells after mitosis), and fruiting bodies have been described as models of multicellular structures. Ustilaginomycetes are Basidiomycota fungi, many of which are pathogens of economically important plant species. These fungi usually grow unicellularly as yeasts (sporidia), but also as simple multicellular forms, such as pseudomycelium, multicellular clusters, or mycelium during plant infection and under different environmental conditions: Nitrogen starvation, nutrient starvation, acid culture media, or with fatty acids as a carbon source. Even under specific conditions, Ustilago maydis can form basidiocarps or fruiting bodies that are complex multicellular structures. These fungi conserve an important set of genes and molecular mechanisms involved in their multicellular growth. In this review, we will discuss in-depth the signaling pathways, epigenetic regulation, required polyamines, cell wall synthesis/degradation, polarized cell growth, and other cellular-genetic processes involved in the different types of Ustilaginomycetes multicellular growth. Finally, considering their short life cycle, easy handling in the laboratory and great morphological plasticity, Ustilaginomycetes can be considered as model organisms for studying fungal multicellularity. Full article
(This article belongs to the Special Issue Microbial Cell Wall)
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18 pages, 764 KiB  
Review
An Intertwined Network of Regulation Controls Membrane Permeability Including Drug Influx and Efflux in Enterobacteriaceae
Microorganisms 2020, 8(6), 833; https://doi.org/10.3390/microorganisms8060833 - 01 Jun 2020
Cited by 18 | Viewed by 3318
Abstract
The transport of small molecules across membranes is a pivotal step for controlling the drug concentration into the bacterial cell and it efficiently contributes to the antibiotic susceptibility in Enterobacteriaceae. Two types of membrane transports, passive and active, usually represented by porins [...] Read more.
The transport of small molecules across membranes is a pivotal step for controlling the drug concentration into the bacterial cell and it efficiently contributes to the antibiotic susceptibility in Enterobacteriaceae. Two types of membrane transports, passive and active, usually represented by porins and efflux pumps, are involved in this process. Importantly, the expression of these transporters and channels are modulated by an armamentarium of tangled regulatory systems. Among them, Helix-turn-Helix (HTH) family regulators (including the AraC/XylS family) and the two-component systems (TCS) play a key role in bacterial adaptation to environmental stresses and can manage a decrease of porin expression associated with an increase of efflux transporters expression. In the present review, we highlight some recent genetic and functional studies that have substantially contributed to our better understanding of the sophisticated mechanisms controlling the transport of small solutes (antibiotics) across the membrane of Enterobacteriaceae. This information is discussed, taking into account the worrying context of clinical antibiotic resistance and fitness of bacterial pathogens. The localization and relevance of mutations identified in the respective regulation cascades in clinical resistant strains are discussed. The possible way to bypass the membrane/transport barriers is described in the perspective of developing new therapeutic targets to combat bacterial resistance. Full article
(This article belongs to the Special Issue Microbial Cell Wall)
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