|dc.description.abstract||Photobacterium profundum SS9 is a γ-proteobacterium which grows optimally at
15°C and 28 MPa (a psychrophilic piezophile) and can grow over a range of
temperatures (2-20oC) and pressures (0.1-90 MPa). Previous research had demonstrated
that P. profundum SS9 adapts its membrane proteins and phospholipids in response to
growth conditions. In this study, methodology was developed for growing P. profundum
SS9 under cold temperatures and high pressures in both liquid and solid cultures. The
effect of changing growth conditions on cell envelope polysaccharides was then
investigated. The lipopolysaccharide (LPS) profile of a rifampicin resistant P.
profundum SS9 derivative, SS9R, was shown to change at 0.1 MPa with respect to
temperature and at 15°C with respect to pressure. Compositional analysis showed that
the LPS was almost entirely composed of glucose. This provides evidence that, under
these conditions, the major polysaccharide produced by P. profundum SS9 is a glucan.
Two putative polysaccharide mutants, FL26 & FL9, were previously isolated
from a screen for cold-sensitive mutants of P. profundum SS9R. Both mutants displayed
an increased sensitivity to cold temperatures on solid medium and were unaffected in
their growth at high pressure. FL26 was found to exhibit an LPS alteration similar to
previously published O-antigen ligase mutants, providing evidence that this mutant is
likely to lack O-antigen ligase. Interestingly, FL26 was also shown to have a reduced
ability to form biofilms and had increased swimming motility. This suggests that there
are a number of changes which occur in FL26 in the absence of O-antigen. FL9 was
found to have an altered LPS and capsular polysaccharide (CPS), similar to an E. coli
wzc mutant. In E. coli, Wzc is involved in the polymerisation and transport of CPS,
disruption of which can also lead to LPS alterations. The LPS and CPS alterations may
lead to the cold-sensitivity phenotype, either individually or in combination.
In conclusion, alterations in the cell envelope polysaccharides were shown to
affect cold temperature sensitivity on solid agar. Cold-sensitivity is most likely directly
related to the LPS alterations and stability of the membrane under cold temperatures.
Exopolysaccharides (EPS) have previously been shown to affect desiccation and freezethaw
resistance, making it is possible that the CPS plays a similar role in this case.||en