A proteomic view of probiotic Lactobacillus rhamnosus GG

Results and Discussion
4. RESULTS AND DISCUSSION
4.1. Eff ect of the growth medium
on the proteome of L.
rhamnosus GG
In study I, the proteomic responses of probiotic
L. rhamnosus GG to growth on two different
types of media, laboratory medium
MRS and an industrial-type whey medium,
were compared. In laboratory studies, the
rich medium MRS is most commonly used
to grow lactobacilli. However, in industrial
large-scale cultivations of lactobacilli, diff erent
types of media, such as those containing milk
components, are used (Siaterlis et al., 2009).
As a consequence, probiotic cells grown in
milk-based media are also frequently used in
clinical studies (Alander et al., 1997; Alander
et al., 1999; Goldin et al., 1992; Isolauri et al.,
1991; Ling et al., 1992; Meurman et al., 1994;
Siitonen et al., 1990). The growth medium
might aff ect the properties of probiotic organisms;
in L. rhamnosus GG and several other
potentially probiotic strains, adhesion properties
were shown to be medium-dependent
(Ouwehand et al., 2001).
Using 2-D DIGE, the proteomes of L.
rhamnosus GG grown in MRS laboratory
medium and hydrolyzed whey medium were
compared at the exponential and stationary
growth phases. Growth medium-dependent
changes were observed in 157 identifi ed protein
spots, which represented 100 distinct
proteins. The most marked change was the
increased production of purine biosynthesis
proteins during the growth of L. rhamnosus
GG in whey medium. Whey medium does not
supply L. rhamnosus GG with purines because
its components are processed from milk,
which is a poor source of purines (Beyer et al.,
34
2003). Th us, an increase in the production of
purine biosynthetic enzymes was expected,
and the need for purine biosynthesis during
growth in milk was previously reported
for lactic acid bacteria (Garault et al., 2001;
Kilstrup et al., 2005).
Another marked growth medium-dependent
change in the proteome patterns was
associated with carbohydrate metabolism proteins.
Th e galactose metabolism enzymes were
produced in higher amounts during growth in
whey medium, and interestingly, the results
indicated that L. rhamnosus GG can degrade
galactose using two different pathways: the
Leloir pathway, which converts galactose
to glucose-6-phosphate, and the tagatose-
6-phosphate pathway, which metabolizes
galactose to glyceraldehyde-3-phosphate and
dihydroxyacetone phosphate (de Vos, 1996;
Poolman, 1993). Th e increased production of
galactose-metabolizing enzymes was expected
because the main sugar in the MRS medium
is glucose, while the whey medium contains
both glucose and galactose, which are derived
from hydrolyzed lactose. Th e growth medium
appeared to also aff ect the balance between
mixed-acid and homolactic acid fermentation
because the proteins required for mixed-acid
fermentation were more abundant in cells
growing in MRS medium. Th is eff ect may be
related to possible diff erences in the redox balance
of L. rhamnosus GG under the two diff erent
growth media conditions (Miyoshi et al.,
2003).
Proteins involved in protein synthesis
were produced at a higher level in MRS
medium, indicating a higher protein synthesis
rate in MRS medium. This result probably
derives from the higher growth rate of