a) A significantly lower proportion of AMP resistance DNA fragments (AMPs, red bars)
conferred resistance in both E. coli and S.
enterica compared to antibiotic resistance DNA fragments (ABs, blue
bars), suggesting weaker between-species conservation of the AMP resistance
phenotypes. Asterisks indicate significant difference,
p=0.0011, two-sided Fisher's exact test,
n=16 for AMPs, n=25 for ABs.
b) The IpxF ortholog from
Parabacteroides merdae, isolated in our screen (marked as
lpxFa here and in Table 1;
represented with green colour) and a previously characterized fully functional
IpxF from Francisella novicida35 (marked as lpxF*)
decrease the net negative surface charge of ΔlpxM E.
coli to a similar extent, and close to the level of wild-type
Bacteroides thetaiotaomicron (BT) expressing its native
lpxF. LpxFa has a similar effect both in
ΔlpxM and wild-type E. coli (dark
and light green dots). The fluorescence signal is proportional to the binding of
the FITC-labeled poly-L-lysine polycationic molecules. Less poly-L-lysine
binding reflects a less negative net cell surface charge36. *, **, *** indicate significant
differences (p=0.03, 0.001 and 0.0004, respectively, Welch
two-sample t-test, n=4 biological replicates, central horizontal bars represent
mean values). Corresponding microscopic pictures are shown in Supplementary Fig. 11.
c) LpxFa increases Polymyxin B resistance of both
ΔlpxM and wild-type E. coli only
five-fold (dark and light green bars) (n=3), to the same extent
as LpxF from Francisella novicida (marked as
lpxF*) (n=3). In contrast,
lpxF in its original host, B.
thetaiotaomicron (marked as lpxF**) provides a
5000-fold increment in Polymyxin B resistance12.