# _Lactobacillus rhamns GG_ as Biosensor for Oral and Systemic Health Conditions: A Pilot Study
## 3 Results and Discussion
This is essential for controlling oxidative stress, particularly in environments like the oral cavity. The protein restores oxidative damage to cells, ensuring they are well functioning. This is crucial for adapting and surviving LGG in various environments, including exposure to human saliva [51]. Changes in the expression or activity of MsrA can demonstrate the general viability and health of LGG cells under various environmental stresses, making it a useful biomarker [52]. In Figure 3d, the PTS System IIA component exhibited distinct expression patterns across LAC, SLFU, SLAN, and SANT. SU10 exhibits the lowest expression level, indicating a reduced need for carbohydrate transport and phosphorylation under normal conditions. SLPA and SLPO exhibit a moderate increase, while SLFU exhibits the highest expression, indicating an increased need for sugar transport and metabolism. This variation implies that SU10 conditions involve either an increased sugar content or increased metabolic activity, requiring efficient carbohydrate uptake. This result also suggests that PTS System IIA is responsive to environmental sugar availability, making it an important regulator of bacterial carbohydrate metabolism. The phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) is one of the main active carbohydrate transport systems in bacteria. The IIA component is part of the enzyme II complex, which is engaged in the phosphorylation and absorption of sugars. This system is crucial in bacterial metabolism and regulation [53]. The PTS system, including the IIA component, is necessary for sugar transport and phosphorylation. This is particularly important in the oral cavity, where bacteria are exposed to a range of dietary sugars [54]. Changes in the expression or activity of the IIA component can reveal how LGG adapts to different environments, making it a valuable biomarker for studying bacterial responses to human saliva and other conditions. In Figure 3e, RPPK levels were lowest in K (control), and SLAN was markedly upregulated in both BUF and SLPO, with SU10 showing the highest expression. The variation suggested that K and SLAN operate under limited nucleotide synthesis demand, reflecting baseline metabolic activity. SLPO and SU10 implied the increased demand for ribose-phosphate and subsequent nucleotide biosynthesis. This may be driven by infection-related proliferation or stress-induced DNA repair. The results emphasized RPPK's role in supporting biosynthetic pathways, particularly during cellular adaptation to environmental pressures or stress. Ribose-phosphate pyrophosphokinase (RPPK), also known as phosphoribosyl pyrophosphate synthetase, is an enzyme that catalyzes the conversion of ribose to 5-phosphate, ultimately forming phosphoribosyl pyrophosphate (PRPP). This reaction is crucial for nucleotide biosynthesis, as well as the production of cofactors and certain amino acids [55]. This regulation helps bacteria adapt to various environmental conditions, such as the presence of saliva. RPPK may be elevated in response to increased demand for nucleotide synthesis, such as during the rapid growth of bacteria. This can occur in environments rich in nutrients or when bacteria must replicate and duplicate their DNA, as the graph's findings indicate that RPPK is upregulated in sucrose [40; 56]. Conversely, RPPK may be downregulated when there is less of a requirement to produce nucleotides, such as in nutrient-poor conditions or when bacterial growth is inhibited. This can help conserve energy and resources. In Figure 3f, Cell Shape-Determining Protein (MreB) expression varied notably across BUFR, SLAN, LAC, and SLPA. BUF and K are comparatively at the lowest levels, suggesting cell morphology maintenance operates at a baseline level in unstressed conditions. SANT, LAC, and SLPA exhibited moderate upregulation, while SLPO and SU10 demonstrated the highest expression, indicating increased cellular remodeling and wall synthesis under stress.