New Iron Acquisition System in Bacteroidetes

Abstract

b Capnocytophaga canimorsus, a dog mouth commensal and a member of the Bacteroidetes phylum, causes rare but often fatal septicemia in humans that have been in contact with a dog. Here, we show that C. canimorsus strains isolated from human infections grow readily in heat-inactivated human serum and that this property depends on a typical polysaccharide utilization locus (PUL), namely, PUL3 in strain Cc5. PUL are a hallmark of Bacteroidetes, and they encode various products, including surface protein complexes that capture and process polysaccharides or glycoproteins. The archetype system is the Bacteroides thetaiotaomicron Sus system, devoted to starch utilization. Unexpectedly, PUL3 conferred the capacity to acquire iron from serotransferrin (STF), and this capacity required each of the seven encoded proteins, indicating that a whole Sus-like machinery is acting as an iron capture system (ICS), a new and unexpected function for Sus-like machinery. No siderophore could be detected in the culture supernatant of C. canimorsus, suggesting that the Sus-like machinery captures iron directly from transferrin, but this could not be formally demonstrated. The seven genes of the ICS were found in the genomes of several opportunistic pathogens from the Capnocytophaga and Prevotella genera, in different isolates of the severe poultry pathogen Riemerella anatipestifer, and in strains of Bacteroides fragilis and Odoribacter splanchnicus isolated from human infections. Thus, this study describes a new type of ICS that evolved in Bacteroidetes from a polysaccharide utilization system and most likely represents an important virulence factor in this group.

Identification of a New Lipoprotein Export Signal in Gram-Negative Bacteria

“…Three of them were recently shown to play critical roles in the biology and pathogenesis of this bacterium (40–42). We address the question of how lipoproteins are targeted to the bacterial surface.…”

Evidence for a LOS and a capsular polysaccharide in Capnocytophaga canimorsus

“…Full length C. canimorsus 5 genes: Ccan_23200 (wzx), Ccan_23280 (wzy), Ccan_15430 (waaL), Ccan_23190 (uge), Ccan_23400 (wbtA), Ccan_15540 (wzz), Ccan_15550 (wza), Ccan_23210 and Ccan_23290 , were amplified from C. canimorsus 5 genomic DNA using primers listed in Supplementary Table S2 and cloned into plasmid pPM578 into Nco I and Xho I restriction sites leading to plasmids listed in Supplementary Table S1. Gene couples Ccan_15540–15550, Ccan_23200–23210 and Ccan_23280–23290 were co-amplified from C. canimorsus 5 genomic DNA and cloned into plasmid pPM578 into Nco I and Xho I restriction sites.…”

“…Gene couples Ccan_15540–15550, Ccan_23200–23210 and Ccan_23280–23290 were co-amplified from C. canimorsus 5 genomic DNA and cloned into plasmid pPM578 into Nco I and Xho I restriction sites.…”

Iron and zinc exploitation during bacterial pathogenesis

“…B. fragilis , however, has the ability to utilize heme and hemoglobin as an iron source, a feature that is associated with it being an opportunistic pathogen and distinguishes itself from the discussion of commensals that take up metals such as the nonpathogenic strains of E. coli 188,189 . Recently, one member of Bacteroidetes phylum demonstrated iron acquisition from transferrin, but the medical significance of this finding is not known 190 .…”