Prolonged Heat Stress of Lactobacillus paracasei GCRL163 Improves Binding to Human Colorectal Adenocarcinoma HT-29 Cells and Modulates the Relative Abundance of Secreted and Cell Surface-Located Proteins

Lactobacillus casei group
bacteria improve cheese
ripening and may interact with host intestinal cells as probiotics,
where surface proteins play a key role. Three complementary methods
[trypsin shaving (TS), LiCl–sucrose (LS) extraction, and extracellular
culture fluid precipitation] were used to analyze cell surface proteins
of Lactobacillus paracasei GCRL163
by label-free quantitative proteomics after culture to the mid-exponential
phase in bioreactors at pH 6.5 and temperatures of 30–45 °C.
A total of 416 proteins, including 300 with transmembrane, cell wall
anchoring, and secretory motifs and 116 cytoplasmic proteins, were
quantified as surface proteins. Although LS caused significantly greater
cell lysis as growth temperature increased, higher numbers of extracytoplasmic
proteins were exclusively obtained by LS treatment. Together with
the increased positive surface charge of cells cultured at supra-optimal
temperatures, proteins including cell wall hydrolases Msp1/p75 and
Msp2/p40, α-fucosidase AlfB, SecA, and a PspC-domain putative
adhesin were upregulated in surface or secreted protein fractions,
suggesting that cell adhesion may be altered. Prolonged heat stress
(PHS) increased binding of L. paracasei GCRL163 to human colorectal adenocarcinoma HT-29 cells, relative
to acid-stressed cells. This study demonstrates that PHS influences
cell adhesion and relative abundance of proteins located on the surface,
which may impact probiotic functionality, and the detected novel surface
proteins likely linked to the cell cycle and envelope stress.