Adherence Enables Neisseria gonorrhoeae to Overcome Zinc Limitation Imposed by Nutritional Immunity Proteins

Abstract

Neisseria gonorrhoeae (Gc) must overcome limitation of metals such as zinc to colonize mucosal surfaces in its obligate human host. While the zinc-binding nutritional immunity proteins calprotectin (S100A8/A9) and psoriasin (S100A7) are abundant in human cervicovaginal lavage fluid, Gc possesses TonB-dependent transporters TdfH and TdfJ that bind and extract zinc from the human version of these proteins, respectively. Here we investigated the contribution of zinc acquisition to Gc infection of epithelial cells of the female genital tract. We found that TdfH and TdfJ were dispensable for survival of strain FA1090 Gc that were associated with Ect1 human immortalized epithelial cells, when zinc was limited by calprotectin and psoriasin. In contrast, suspension-grown bacteria declined in viability under the same conditions. Exposure to murine calprotectin, which Gc cannot use as a zinc source, similarly reduced survival of suspension-grown Gc, but not Ect1-associated Gc. We ruled out epithelial cells as a contributor to the enhanced growth of cell-associated Gc under zinc limitation. Instead, we found that attachment to glass was sufficient to enhance bacterial growth when zinc was sequestered. We compared the transcriptional profiles of WT Gc adherent to glass coverslips or in suspension, when zinc was sequestered with murine calprotectin or provided in excess, from which we identified open reading frames that were increased by zinc sequestration in adherent Gc. One of these, ZnuA, was necessary but not sufficient for survival of Gc under zinc-limiting conditions. These results show that adherence protects Gc from zinc-dependent growth restriction by host nutritional immunity proteins.

Metal piracy by Neisseria gonorrhoeae to overcome human nutritional immunity

“…gonorrhoeae in metal-stripped chemically defined medium; conversely, calprotectin sequesters zinc in metal-replete tissue culture medium such that N . gonorrhoeae growth is TdfH-dependent [ 10 , 26 ]. While N .…”

“…While TdfH and TdfJ are required for planktonic growth of N . gonorrhoeae in medium where zinc is sequestered by calprotectin and psoriasin, they are surprisingly dispensable for bacteria that are adherent to cells or abiotic surfaces [ 26 ]. N .…”

“…gonorrhoeae exhibits distinct transcriptional profiles between adherent and planktonic states, and in zinc-replete versus deplete conditions: Genes that are significantly up-regulated in zinc-limited, adherent N . gonorrhoeae encode the periplasmic metal-binding proteins ZnuA and FbpA, as well as metabolic proteins not previously associated with metal homeostasis [ 26 ]. Thus, N .…”

“…For zinc acquisition, N. gonorrhoeae extracts zinc from human calprotectin and psoriasin, using TdfH and TdfJ, respectively [10,[23][24][25]. Zinc-loaded calprotectin supports zinc-dependent growth of N. gonorrhoeae in metal-stripped chemically defined medium; conversely, calprotectin sequesters zinc in metal-replete tissue culture medium such that N. gonorrhoeae growth is TdfH-dependent [10,26]. While N. gonorrhoeae does not produce siderophores, FetA enables the uptake of siderophores made by other microbes, and FetBCD drive import into the cytosol [27].…”

“…While TdfH and TdfJ are required for planktonic growth of N. gonorrhoeae in medium where zinc is sequestered by calprotectin and psoriasin, they are surprisingly dispensable for bacteria that are adherent to cells or abiotic surfaces [26]. N. gonorrhoeae exhibits distinct transcriptional profiles between adherent and planktonic states, and in zinc-replete versus deplete conditions: Genes that are significantly up-regulated in zinc-limited, adherent N. gonorrhoeae encode the periplasmic metal-binding proteins ZnuA and FbpA, as well as metabolic proteins not previously associated with metal homeostasis [26]. Thus, N. gonorrhoeae has evolved specific adaptations to respond to and resist host-mediated metal starvation.…”