Capsular polysaccharides and exopolysaccharides play critical roles in bacterial survival strategies, and they can have important medical and industrial applications. An immense variety of sugars and glycosidic linkages leads to an almost unlimited diversity of potential polysaccharide structures. This diversity is reflected in the large number of serologically and chemically distinct polysaccharides that have been identified among both gram-positive and gram-negative bacteria. Despite this diversity, however, the genetic loci and mechanisms responsible for polysaccharide biosynthesis exhibit conserved features and can be classified into a small number of groups. In Streptococcus pneumoniae, capsule synthesis occurs by one of two distinct mechanisms that involve the polymerization of either individual sugars in a processive reaction (synthase dependent) or discrete repeat units in a nonprocessive reaction (Wzy dependent). Characterization of these systems has provided novel insights that are applicable to polymers synthesized by many gram-positive and gram-negative bacteria, as well as eukaryotes.

Capsules of Streptococcus pneumoniae and Other Bacteria: Paradigms for Polysaccharide Biosynthesis and Regulation

The ability to produce polysaccharides with diverse biological functions is widespread in bacteria. In lactic acid bacteria (LAB), production of polysaccharides has long been associated with the technological, functional and health-promoting benefits of these microorganisms. In particular, the capsular polysaccharides and exopolysaccharides have been implicated in modulation of the rheological properties of fermented products. For this reason, screening and selection of exocellular polysaccharide-producing LAB has been extensively carried out by academia and industry. To further exploit the ability of LAB to produce polysaccharides, an in-depth understanding of their biochemistry, genetics, biosynthetic pathways, regulation and structure-function relationships is mandatory. Here, we provide a critical overview of the latest advances in the field of glycosciences in LAB. Surprisingly, the understanding of the molecular processes involved in polysaccharide synthesis is lagging behind, and has not accompanied the increasing commercial value and application potential of these polymers. Seizing the natural diversity of polysaccharides for exciting new applications will require a concerted effort encompassing in-depth physiological characterization of LAB at the systems level. Combining high-throughput experimentation with computational approaches, biochemical and structural characterization of the polysaccharides and understanding of the structure-function-application relationships is essential to achieve this ambitious goal.

Polysaccharide production by lactic acid bacteria: from genes to industrial applications.

Beyond gene expression: the impact of protein post-translational modifications in bacteria.

Protein modifications not only affect protein homeostasis but can also establish new cellular protein functions and are important components of complex cellular signal sensing and transduction networks. Among these post-translational modifications, protein phosphorylation represents the one that has been most thoroughly investigated. Unlike in eukarya, a large diversity of enzyme families has been shown to phosphorylate and dephosphorylate proteins on various amino acids with different chemical properties in bacteria. In this review, after a brief overview of the known bacterial phosphorylation systems, we focus on more recently discovered and less widely known kinases and phosphatases. Namely, we describe in detail tyrosine- and arginine-phosphorylation together with some examples of unusual serine-phosphorylation systems and discuss their potential role and function in bacterial physiology, and regulatory networks. Investigating these unusual bacterial kinase and phosphatases is not only important to understand their role in bacterial physiology but will help to generally understand the full potential and evolution of protein phosphorylation for signal transduction, protein modification and homeostasis in all cellular life.

https://orbit.dtu.dk/files/123704243/Exploring_the_diversity_of_protein_modifications.pdf

Exploring the diversity of protein modifications: special bacterial phosphorylation systems

Microbial protein-tyrosine kinases.

When considering protein phosphorylation in bacteria, phosphorylation of aspartic acid and histidine residues mediated by the two-component systems is the first to spring to mind. And yet other phosphorylation systems have been described in bacteria in the past 20 years including eukaryotic-like serine/threonine kinases and more recently tyrosine-kinases. Among the latter, a peculiar type is widespread among bacteria, but not in higher organisms. These enzymes possess unique structural features defining thus a new family of enzymes termed Bacterial tyrosine kinases (BY-kinases). BY-kinases have been shown to be mainly involved in polysaccharide production, but their ability to phosphorylate endogenous substrates indicates that they participate in the regulation of other functions of the bacterial cell. Recent advances in mass spectrometry based phosphoproteomics provided lists of many new phosphotyrosine-proteins, indicating that BY-kinases may be involved in regulating a large array of other cellular functions. One may expect that in a near future, tyrosine phosphorylation will turn out to be one of the key regulatory processes in the bacterial cell and will yield new insights into the understanding of its physiology.

Tyrosine-kinases in bacteria: from a matter of controversy to the status of key regulatory enzymes.

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Tyrosine-kinases in bacteria: from a matter of controversy to the status of key regulatory enzymes.