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1. (Article ID: 5500)
 
Singh JK, Adams FG, Brown MH
Diversity and Function of Capsular Polysaccharide in Acinetobacter baumannii
Frontiers in Microbiology 9 (2019) 3301
 

The Gram-negative opportunistic bacterium Acinetobacter baumannii is a significant cause of hospital-borne infections worldwide. Alarmingly, the rapid development of antimicrobial resistance coupled with the remarkable ability of isolates to persist on surfaces for extended periods of time has led to infiltration of A. baumannii into our healthcare environments. A major virulence determinant of A. baumannii is the presence of a capsule that surrounds the bacterial surface. This capsule is comprised of tightly packed repeating polysaccharide units which forms a barrier around the bacterial cell wall, providing protection from environmental pressures including desiccation and disinfection regimes as well as host immune responses such as serum complement. Additionally, capsule has been shown to confer resistance to a range of clinically relevant antimicrobial compounds. Distressingly, treatment options for A. baumannii infections are becoming increasingly limited, and the urgency to develop effective infection control strategies and therapies to combat infections is apparent. An increased understanding of the contribution of capsule to the pathobiology of A. baumannii is required to determine its feasibility as a target for new strategies to combat drug resistant infections. Significant variation in capsular polysaccharide structures between A. baumannii isolates has been identified, with over 100 distinct capsule types, incorporating a vast variety of sugars. This review examines the studies undertaken to elucidate capsule diversity and advance our understanding of the role of capsule in A. baumannii pathogenesis.

polysaccharide, Acinetobacter, Acinetobacter baumannii, capsule, virulence factor, persistence

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2. (Article ID: 5791)
 
Knirel YA, Van Calsteren M
Bacterial exopolysaccharides
Book: Comprehensive Glycoscience: From Chemistry to Systems Biology. Reference Module in Chemistry, Molecular Sciences and Chemical Engineering (2021) 1-75
 

Bacterial extracellular polysaccharides are known as a cell-bound capsule, a sheath, or a slime, which is excreted into the environment. They play an important role in virulence of medical bacteria and plant-to-symbiont interaction and are used for serotyping of bacteria and production of vaccines. Some exopolysaccharides have commercial applications in industry, and claims of health benefits have been documented for an increasing number of them. Exopolysaccharides have diverse composition and structure, and some contain sugar and non-sugar components that are found in bacterial carbohydrates only. The present article provides an updated collection of the data on exopolysaccharides of various classes of gram-negative and gram-positive bacteria reported until the end of 2019. When known, biosynthesis pathways of exopolysaccharides are treated in a summary manner. References are made to structure and biosynthesis relatedness between exopolysaccharides of different bacterial taxa as well as between bacterial polysaccharides and mammalian glycosaminoglycans.

polysaccharide structure, Gram-negative bacteria, capsule, Biofilm, polysaccharide biosynthesis, gram-positive bacteria, Monosaccharide composition, Bacterial exopolysaccharide, non-sugar component

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3. (Article ID: 6411)
 
Kasimova AA, Sharar NS, Ambrose SJ, Knirel YA, Shneider MM, Timoshina OY, Popova AV, Perepelov AV, Dmitrenok AS, Hsu LY, Hall RM, Kenyon JJ
The Acinetobacter baumannii K70 and K9 capsular polysaccharides consist of related K-units linked by the same Wzy polymerase and cleaved by the same phage depolymerases
Microbiology Spectrum 11(6) (2023) e0302523
 

Bacteriophage show promise for the treatment of Acinetobacter baumannii infections that resist all therapeutically suitable antibiotics. Many tail-spike depolymerases encoded by phage that are able to degrade A. baumannii capsular polysaccharide (CPS) exhibit specificity for the linkage present between K-units that make up CPS polymers. This linkage is formed by a specific Wzy polymerase, and the ability to predict this linkage using sequence-based methods that identify the Wzy at the K locus could assist with the selection of phage for therapy. However, little is known about the specificity of Wzy polymerase enzymes. Here, we describe a Wzy polymerase that can accommodate two different but similar sugars as one of the residues it links and phage depolymerases that can cleave both types of bond that Wzy forms.

Acinetobacter baumannii, capsular polysaccharide, Wzy polymerase, phage depolymerase, K70

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4. (Article ID: 6413)
 
Knirel YA, Kasimova AA, Arbatsky NP, Shneider MM, Popova AV, Brovko FA, Shashkov AS, Senchenkova SN, Perepelov AV, Shpirt AM
5,7-Diamino-3,5,7,9-tetradeoxynon-2-ulosonic Acids in the Capsular Polysaccharides of Acinetobacter baumannii
Biochemistry (Moscow) 88(2) (2023) 202-210
 

The polysaccharide capsule surrounding bacterial cell plays an important role in pathogenesis of infections caused by the opportunistic pathogen Acinetobacter baumannii by providing protection from external factors. The structures of the capsular polysaccharide (CPS) produced by A. baumannii isolates and the corresponding CPS biosynthesis gene clusters are highly diverse, although many of them are related. Many types of A. baumannii CPSs contain isomers of 5,7-diamino-3,5,7,9-tetradeoxynon-2-ulosonic acid (DTNA). Three of these isomers, namely acinetaminic acid (l-glycero-l-altro isomer), 8-epiacinetaminic acid (d-glycero-l-altro isomer), and 8-epipseudaminic acid (d-glycero-l-manno isomer), have not been found so far in naturally occurring carbohydrates from other species. In A. baumannii CPSs, DTNAs carry N-acyl substituents at positions 5 and 7; in some CPSs, both N-acetyl and N-(3-hydroxybutanoyl) groups are present. Remarkably, pseudaminic acid carries the (R)-isomer and legionaminic acid carries the (S)-isomer of the 3-hydroxybutanoyl group. The review addresses the structure and genetics of biosynthesis of A. baumannii CPSs containing di-N-acyl derivatives of DTNA.

Acinetobacter baumannii, capsular polysaccharide, nonulosonic acid, Bacterial polysaccharide, capsule, higher monosaccharide, acyl group

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