Biogenesis of the outer membrane (OM) in Gram-negative bacteria, which is essential for viability, requires the coordinated transport and assembly of proteins and lipids, including lipopolysaccharides (LPS) and phospholipids (PLs), into the membrane. While pathways for LPS and OM protein assembly are well-studied, how PLs are transported to and from the OM is not clear. Mechanisms that ensure OM stability and homeostasis are also unknown. The trans-envelope Tol-Pal complex, whose physiological role has remained elusive, is important for OM stability. Here, we establish that the Tol-Pal complex is required for PL transport and OM lipid homeostasis in Escherichia coli. Cells lacking the complex exhibit defects in lipid asymmetry and accumulate excess PLs in the OM. This imbalance in OM lipids is due to defective retrograde PL transport in the absence of a functional Tol-Pal complex. Thus, cells ensure the assembly of a stable OM by maintaining an excess flux of PLs to the OM only to return the surplus to the inner membrane. Our findings also provide insights into the mechanism by which the Tol-Pal complex may promote OM invagination during cell division.

Summary 15Biogenesis of the outer membrane (OM) in Gram-negative bacteria, which is essential for

Edited by Karen G. Fleming The outer membrane (OM) of Gram-negative bacteria exhibits unique lipid asymmetry, with lipopolysaccharides (LPS) residing in the outer leaflet and phospholipids (PLs) in the inner leaflet. This asymmetric bilayer protects the bacterium against intrusion of many toxic substances, including antibiotics and detergents, yet allows acquisition of nutrients necessary for growth. To build the OM and ensure its proper function, the cell produces OM constituents in the cytoplasm or inner membrane and transports these components across the aqueous periplasmic space separating the two membranes. Of note, the processes by which the most basic membrane building blocks, i.e. PLs, are shuttled across the cell envelope remain elusive. This review highlights our current understanding (or lack thereof) of bacterial PL trafficking, with a focus on recent developments in the field. We adopt a mechanistic approach and draw parallels and comparisons with well-characterized systems, particularly OM lipoprotein and LPS transport, to illustrate key challenges in intermembrane lipid trafficking. Pathways that transport PLs across the bacterial cell envelope are fundamental to OM biogenesis and homeostasis and are potential molecular targets that could be exploited for antibiotic development.

Pseudomonas putida CSV86 utilizes aromatic compounds in preference to glucose and coutilizes aromatics and organic acids. Protein analysis of cells grown on different carbon sources, either alone or in combination, revealed that a 43-kDa periplasmic-space protein was induced by glucose and repressed by aromatics and succinate. Two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometry analysis identified this protein as closely resembling the sugar ABC transporter of Pseudomonas putida KT2440. A partially purified 43-kDa protein showed glucose binding activity and was specific for glucose. The results demonstrate that the aromatic-and organic acid-mediated repression of a periplasmic-space glucose binding protein and consequent inhibition of glucose transport are responsible for this strain's ability to utilize aromatics and organic acids in preference to glucose.

The severe acute respiratory syndrome is a viral respiratory infection and commonly called as COVID-19, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). It widely transmitted through direct or indirect contact. Currently, no specific treatment against SARS-CoV-2 are available; only prevention and supportive strategy are the preventive measures. The present review emphasizes the latest research related to COVID-19 and SARS-CoV-2 virus as well as the current status of potential inhibitors identified. Recent interest in SARS-CoV-2 has focused on transmission, symptoms, structure, and its structural proteins that exhibit promising therapeutics targets for rapid identification of potential inhibitors. The quick identification of potential inhibitors and immune-boosting functional food ingredients are crucial to combat this pandemic disease. We also tried to give an overview of the functional food components as a nutritional supplement, which helps in boosting our immune system and could be useful in preventing the COVID-19 and/or to improve the outcome during therapy.

Aromatic compounds pose a major threat to the environment, being mutagenic, carcinogenic, and recalcitrant. Microbes, however, have evolved the ability to utilize these highly reduced and recalcitrant compounds as a potential source of carbon and energy. Aerobic degradation of aromatics is initiated by oxidizing the aromatic ring, making them more susceptible to cleavage by ring-cleaving dioxygenases. A preponderance of aromatic degradation genes on plasmids, transposons, and integrative genetic elements (and their shuffling through horizontal gene transfer) have lead to the evolution of novel aromatic degradative pathways. This enables the microorganisms to utilize a multitude of aromatics via common routes of degradation leading to metabolic diversity. In this review, we emphasize the exquisiteness and relevance of bacterial degradation of aromatics, interlinked degradative pathways, genetic and metabolic regulation, carbon source preference, and biosurfactant production. We have also explored the avenue of metagenomics, which opens doors to a plethora of uncultured and uncharted microbial genetics and metabolism that can be used effectively for bioremediation.

Pseudomonas putida CSV86 shows preferential utilization of aromatic compounds over glucose. Protein analysis and [ 14 C]glucose-binding studies of the outer membrane fraction of cells grown on different carbon sources revealed a 40 kDa protein that was transcriptionally induced by glucose and repressed by aromatics and succinate. Based on 2D gel electrophoresis and liquid chromatography-tandem mass spectrometry analysis, the 40 kDa protein closely resembled the porin B of P. putida KT2440 and carbohydrate-selective porin OprB of various Pseudomonas strains. The purified native protein (i) was estimated to be a homotrimer of 125 kDa with a subunit molecular mass of 40 kDa, (ii) displayed heat modifiability of electrophoretic mobility, (iii) showed channel conductance of 166 pS in 1 M KCl, (iv) permeated various sugars (mono-, di-and trisaccharides), organic acids, amino acids and aromatic compounds, and (v) harboured a glucosespecific and saturable binding site with a dissociation constant of 1.3 mM. These results identify the glucose-inducible outer-membrane protein of P. putida CSV86 as a carbohydrate-selective protein OprB. Besides modulation of intracellular glucose-metabolizing enzymes and specific glucose-binding periplasmic space protein, the repression of OprB by aromatics and organic acids, even in the presence of glucose, also contributes significantly to the strain's ability to utilize aromatics and organic acids over glucose.

No abstract