## 9 Role of PPCs in the Molecular Adaptation of _Lactobacillus_ to Host Environments
#### 9.2.2 Teichoic Acids  
The different biochemical properties (chain length, backbone composition, or degree of glycosyl substitution) and production levels of cell wall teichoic acids (WTA) and lipoteichoic acids (LTA) are directly related to the immunodulatory capacity of _Lactobacillus_ spp. [104] and severely impact its capacity to communicate with their hosts [68]. The expression of several enzymes implicated in the biosynthesis or modification of _L. plantarum_ teichoic acids that are associated with altered host responses, including TagE6, Tag D2,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Locus Tags** & \multicolumn{2}{c}{**PPC Effector (Ref.) a**} & \multicolumn{2}{c}{**Effect**} & \multicolumn{1}{c}{**Phenotype Involved**} \\ \hline \multicolumn{4}{c}{**Other mechanisms**} \\ \hline \multicolumn{4}{c}{**Oxidative stress**} \\ \hline _npr2_ & NADH-peroxidase & _p_-CA, OLE, HXT & + & \\ _kat_ & catalase & HXT & + & \\ _pox_ & pyruvate oxidase & OLE, HXT & + & Resistance against oxidative \\ _trxA1, trxA; trxB1_ & thioerdoxin; thioredoxin reductase & _p_-CA & + & stress at mucosal surface of \\ _tpx_ & thiol peroxidase & _p_-CA & + & the colon (putative) [94] \\ _gshR4_ & glutathione reductase & HXT & + & \\ _lp\_0858_ & redox protein, peroxiredoxin & HXT & + & \\ \hline \hline \multicolumn{4}{c}{**Peptidesvcan remodeling**} \\ \hline \multicolumn{4}{c}{} & TA [37] & + & cell envelope under GIT \\ LDH-D & d-lactate dehydrogenase & Rutin [45] & + & stress (bile, osmotic and \\ \multicolumn{4}{c}{} & acid stresses) (putative) [87] \\ DAPF & diaminopimelate (DAP) epimerase & TA [37] & + & \\ GLMU & UDP-\(N\)-acetylglucosamine & Rutin [45] & + & \\ _aad_ & d-alanyl-d-alanine dipeptidase & _p_-CA & + & \\ _hicD2_ & d-hydroxyiscaproate & _p_-CA & + & \\ _lp\_0302\_lp\_3014_; & dehydrogenase & & + & \\ _lp\_3015_ & lytic transglycos & _p_-CA & \(-\) & \\ \hline \multicolumn{4}{c}{**Compatible solutes**} \\ \hline \multicolumn{4}{c}{} & glycine betaine/carnitine/choline \\ _lp\_3324_ & transport protein & _p_-CA, HXT & \(-\) & Osmoprotection against \\ _glpr4_ & glycerol uptake facilitator protein & _p_-CA & \(-\) & osmotic stress in the GIT \\ _ptsSABC_ & PTS system specific- trehalose & HXT & \(-\) & (putative) [87; 94] \\ \hline \hline \end{tabular}  
* Reference describing the regulation of the molecular actor (gene or protein) by the plant phenolic compound. _p_-CA (_p_-cumaric acid), RSV (resveratrol), OLE (oleuropein), HXT (hydroxytrosyl), TA (tannic acid);
* reference describing the phenotype associated with the molecular actor (gene or protein); +, upregulation; \(-\), downregulation.  
\end{table}
Table 3: _Cont._enzymes encoded by the _tarI_JKL locus, and the LTA glycosylation protein encoded by the _geta_I gene, were differently regulated by various PPCs, mainly OLE and HXT (Table 4).  
According to these observations, exposure to these PPCs is expected to modify the signaling ability of _L. plantarum_ and its capacity to communicate with their hosts. This notion is strongly supported in the case of OLE [28] as exposure to this PPC also modifies the expression of other documented immunomodulators from this microorganism, including components of the plantaric and LamBDCA quorum-sensing systems [105; 106; 107; 108].