Weizmannia coagulans
can be used as a starter strain in fermented foods or as a probiotic. However, it is salt-sensitive. Here,
W. coagulans
genomes were compared with the genomes of strains of
Bacillus
species (
B. licheniformis
,
B. siamensis
,
B. subtilis
, and
B. velezensis
) that were isolated from fermented foods and show salt tolerance, to identify the basis for the salt-sensitivity of
W. coagulans
. Osmoprotectant uptake (Opu) systems transport compatible solutes into cells to help them tolerate osmotic stress.
B. siamensis
,
B. subtilis
, and
B. velezensis
each possess five Opu systems (OpuA, OpuB, OpuC, OpuD, and OpuE);
B. licheniformis
has all except OpuB. However,
W. coagulans
only has the OpuC system. Based on these findings, the
opuA
and
opuB
operons, and the
opuD
and
opuE
genes, were amplified from
B. velezensis
. Expression of each of these systems, respectively, in
W. coagulans
increased salt-tolerance.
W. coagulans
expressing
B. velezensis
opuA
,
opuD
, or
opuE
grew in 10.5% NaCl (w/v), whereas wild-type
W. coagulans
could not grow in 3.5% NaCl. The salt resistance of
B. subtilis
was also increased by overexpression of
B. velezensis
opuA
,
opuB
,
opuD
, or
opuE
. These results indicate that the salt-susceptibility of
W. coagulans
arises because it is deficient in Opu systems.