FbsA-Driven Fibrinogen Polymerization: A Bacterial “Deceiving Strategy”

We show that FbsA, a cell wall protein of the bacterium Streptococcus agalactiae, promotes large-scale aggregation of human plasma fibrinogen, leading to the formation of a semiflexible polymerlike network. This extensive aggregation process takes place not only in solution, but also on FbsA-functionalized colloidal particles, and leads to the formation of a thick layer on the bacterial cell wall itself, which becomes an efficient mask against phagocytosis.

Figure 1

Main body: $g(t)$ for a $\mathrm{Fbg}+\mathrm{FbsA}$ solution at molar ratio $1:10$ taken 8, 25, 40, and 100 min after mixing (●, from left to right) and for pure Fbg (○). Full lines are stretched exponential fits to $g(t)$ for $t_{\mathrm{agg}}\gtrsim {10}^3\mathrm{s}$. Inset A: Semilog plot of the short-time behavior for the same data. Inset B: Short-time (○) and average (●) decay time of $g(t)$.

Figure 2

Main body: Data obtained or $\mathrm{FbsA}+\mathrm{Fbg}$ solutions at molar ratios $1:10$ at various scattering angles 1 h after mixing as a function of $\Gamma t$, where $\Gamma =1/\tau$ is the short-time decay rate. The $q$ dependence of the stretch exponent $\alpha$ and of the short-time decay $\Gamma$ are shown in the Insets A and B.

Figure 3

(a) SEM image of a dried $\mathrm{FbsA}+\mathrm{Fbg}$ solution at $1:10$ molar ratio. A SEM image of a fibrin gel is shown for comparison in the small upper inset. (b) Fluorescence image of Fbg aggregation of FbsA-laden colloids. (c) Fluorescence image of Fbg localization on GBS cells. The same field is shown in (d) as a DIC image. Scale bars correspond to $10\mu \mathrm{m}$.