IndraLab

"This reaction is catalyzed by the enzyme Glucosamine-6-phosphate deaminase (NagB), an aldose-ketose isomerase that is tightly regulated and is part of the conserved nag-nan operon of many Gram-negative bacteria [ xref , xref ]."

"Loci VC1758 to VC1809 ( nan-nag gene cluster) present in the VPI-2 was identified to be involved in the transport and catabolism of sialic acid (Almagro-Moreno and Boyd, xref )."

"In the case of prokaryotes, these sialic acids are decorated as the outermost moiety of the lipooligosaccharide/lipopolysaccharide (LOS/LPS) on their cell membranes. xref − xref Pathogenic bacteria such as Haemophilus influenzae ( Hi ) , Pasteurella multocida ( Pm ) , Vibrio cholerae ( Vc ), and Fusobacterium nucleatum ( Fn ) that reside in the host mucous-rich environments of the gut and respiratory tract scavenge sialic acids from the host and transport them into bacteria using the TRAP transport system. xref , xref Post scavenging sialic acids from the host, these bacteria incorporate a part of the scavenged sialic acid as the outermost sugar on their LOS/LPS to evade the host immune system; this phenomenon is known as “molecular mimicry”. xref − xref Furthermore, these bacteria use sialic acids as a carbon and nitrogen source by converting them into fructose 6-phosphate using the enzymes of the nan-nag gene cluster (NanA, NanK, NanE, NagA, and NagB) ( xref ."

"Interestingly, all O47 isolates contained the nan-nag GC, related to sialic acid metabolism, found to be part of VPI-2."

"These islets include Islet A (Type 1 Restriction modification system, VC1764 to VC1769), Islet B (Nan-Nag cluster, VC1773 to VC1784), Islet C (Mu phage-like region, VC1791 to VC1799), and Islet D with unknown function (VC1804 to VC1809) [ xref ]."

"This capability is encoded within the island’s nan-nag genomic region ( xref xref xref )."

"Prior studies have reported that NOVCs causing gastroenterological diseases often encode a truncated VPI-2 with the Nan-Nag gene cluster [ xref , xref ]."

"Our analysis confirmed the island’s modular structure as described by Jermyn and Boyd ( xref , xref ), including a predicted Zorya system ( xref ) encoded by genes VC1761–64 [as per reference strain N16961; ( xref )], a predicted T1RM system ( VC1765–69 ) ( xref ), the DdmDE defense module ( VC1770–71) ( xref ), the nan-nag sialic acid utilization cluster ( VC1773–1784 ), and a region with phage-like properties ( VC1791–1809 ) ( xref ) ( xref )."

"While all four V. cholerae O47 isolates harbored a truncated version of VPI-2 containing the nan-nag region, Mathbaria V. cholerae O47 isolates ( xref ) lacked the two gene DNA defense module (VC01770-VC01771) associated with elimination/destabilization of plasmids in seventh pandemic V. cholerae ( xref )."

"Hence, we investigated the two gene clusters essential for the uptake and metabolism of sialic acid, the nagA2-nagB3 cluster (Bbr_1247-Bbr_1248) and the nan-nag cluster (Bbr_0160-Bbr_0172) ( xref xref xref )."

"The enzymes involved in sialic acid catabolism are generally found in the tightly regulated nan–nag operon (Almagro-Moreno & Boyd, 2010 xref )."

"In VPI-2, all the O139 with the exception of two isolates lacked nearly one third of the island encoding type I restriction modification systems nan-nag region including the most important neuraminidase gene ( nanH ); whereas only the phage-like region has been retained (~20 kb)."

"Since O139 VPI-2 lacks the notable regions of the  nan-nag gene clusters, its persistence in the environment and sensitivity of host cells to the cytotoxin ( ctxb) has been highly limited xref ."

"Further, the absence of the nan-nag gene cluster in O139 may not allow the strains to grow in the mucus rich gut environment with high sialic acids xref ."

"This supports the lack of competitive advantage of O139 strains being more pathogenic in the host colonization as compared to O1 7PET strains that harbors complete VPI-2 with functional nan-nag regions."

"We found that this GI of ~64 kb is inserted in the tRNA- ser gene and located next to a nan-nag region involved in the sialic acid catabolism ( xref ), which is also harboured by the VPI-II [ xref ]."