More than 700 bacterial species have been identified in

More than 700 bacterial species have been identified in the human oral cavity. Among them, Fusobacterium nucleatum is frequently isolated from both supra and sub-gingival dental plaque biofilm in human. F. nucleatum is a Gram-negative, non-motile, anaerobic, spindle-shaped and non-spore-forming bacterium. It plays a vital role in dental plaque biofilm formation1. Over the course of evolution, eukaryotes have incorporated sialic acids in lots of functions2, which majorly involves cell-cell and cell-molecule interactions on the cell membrane which acts as a chemical messenger.  These types of interaction are mediated by the formation of glycoconjugates that have sialic acids bound to the terminating branches of N-glycans, O-glycans and glycosphingolipids moieties3. Thus, the presence of sialic acid is crucial for the development of vertebrates. Premature deaths of mice embryo have been observed in models which have sialic acid biosynthesis genes subjected to inactivation by gene targeting4.

 

Sialic acid is a 9-carbon, acidic, alpha keto sugar which belongs to a family of more than 50 structurally distinct sialic acids. The most common form of sialic acid is N-acetylneuraminic acid (Neu5Ac)5,6. Neu5Ac is extensively studied in eukaryotes and prokaryotes, therefore, at times it is interchangeably referred to as sialic acid7,8,9.The incredible structural diversity and broad distribution of sialic acids in nature make sialic acids strongly important in cell biology. At physiological pH, the carboxyl group of sialic acids is usually deprotonated, allowing sialic acids a net negative charge10. The pathways for biosynthesis of Neu5Ac were majorly worked by the groups led by Saul Roseman and Leonard Warren. Until recently, these sugars were thought to exist only in “higher” animals (starfish to humans) and a few pathogenic bacterial species. The few, mostly pathogenic, bacterial species that were known to synthesize sialic acids11 were thought to represent either a relatively recent and minor parallel evolution of the pathway or acquisition of biosynthetic genes from eukaryotes by horizontal gene transfer12. After a period of time, sialic acid bound glycoconjugates are removed by sialdiase, which is an enzyme of the hydrolase class. Several pathogenic bacteria like Escherichia coli, Haemophilus influenzae, H. ducreyi, Pasteurella multocida, Neisseria gonorrhoeae, N. meningitidis, etc can put sialic acid residues on their outer surfaces (sialylated) masking them from the host immune system13,14,15,16,17,18,19. Apart from these, sialic acids like Neu5Ac found its way in having commercial significance in the food and pharmaceutical industry. It is used as additive various dairy products for its ability to strengthen the immuni

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