## 3 Results
### Analysis of Relative Gene Expression in Co-Culture
rhamnus_ ATCC 9595, the percentage of over-expressed genes was limited to 50% (_galR_, _ackA_, _fbp_, and _pyK_) between six and 12 h, while genes _lacT_, _fbp galK_, and _galR_ were under-expressed between 15 and 24 h. Pyruvate kinase (_pyk_) was over-expressed (RER of 3.517, \(P\) = 0.000) during 80% of experience duration (6, 12, 15, and 24 h). In contrast, _L. rhamnus_ RW-9595M showed an over-expression of 75% of target genes for this group (_galK_, _bgaC_, _galE_, _lacT_, _galR_, _lacD_, _fbp_ and _ackA_) at 6, 9, and 12 h of fermentation. Tagatose 1,6-diphosphate aldolase gene (_lacD_) was over-expressed for 80% of the samples (6, 9, 12, 15 and 24 h) in co-culture compared with monoculture. The largest change in gene expression was found for the _bgaC_ gene (RER = 10.247, \(P\) = 0.007) after 6 h of fermentation. (ii) Group 2: EPS operons (G2)  
In all strains, exopolysaccharidesacharide biosynthesis was influenced by yeast presence. _L. rhamnus_ R0011 showed over-expression of genes _wzm_, _rmLA_, _rmLD_, _wzb_ and _wvelE_ after 6 and 12 h (RER between 1.972 and 7.056 \(P\) \(<\) 0.05). However, gene _wzd_ was under-expressed in co-culture during 60% of the fermentation time when compared to monoculture. _L. rhamnus_ ATCC 9595 exhibited an over-expression of genes _wzb_, _wvelE_, and _nrp_ after 6 h (RER 1.452, 1.865 and 2.416 \(P\) \(<\) 0.05, respectively) and _wzd_ after 9 and 24 h (RER 1.803 and 1.484 \(P\) \(<\) 0.05, respectively). After 15 hours, _wzr_, _wzb_, _wvelE_, and _nrp_ were under-expressed. The _rmLD_ gene was under-expressed during 60% of the fermentation time. Strain RW-9595M showed more than 60% of targeted genes for the EPS operon (_wzd_, _wzm_, _rmLA_, _wzr_, _wzb_, _wvelE_, and _nrp_) were over-expressed after 6, 9, and 12 h (RER ranging between 2.951 and 11.522 \(P\) \(<\) 0.05). After 24 hours, the _rmID_ gene was significantly under-expressed in co-culture (RER \(-\)1.595 \(P\) = 0.001). (iii) Group 3: Amino acid biosynthesis and lipid metabolism (G3)  
In all tested strains, amino acid biosynthesis and lipid metabolism were influenced significantly by the presence of _S. cerevisiae_. For the R0011 strain, the over-expressed genes were: _cySK_, _fabG_, _ami_, _R0011_RS11250_, and _metC_ (RER ranging between 1.504 and 3.485 \(P\) \(<\)0.05) after 6 and 12 h. After 15 hours, genes coding for _metC_, _metA_, _R0011_RS11250_ and _cfa_ were under-expressed in co-culture (RER ranging between \(-\)1.761 and \(-\)3.984 \(P\) \(<\) 0.01). _L. rhamn_ ATCC 9595 had 50% of target genes (_R0011_RS4490_, _ami_, _R0011_RS11250_, and _cfa_) over-expressed after 15 h (RER ranging between 3.671 and 5.175 \(P\) \(<\) 0.05). In contrast, after 24 h, most target genes (\(>\) 80%) were under-expressed in relation to monoculture (RER ranging between \(-\)2.075 and \(-\)21.739 \(P\) \(<\) 0.01). _L. rhamn_RW-9595M showed two trends: a strong over-expression after 9 hours for 80% of targeted genes (_cySK_, _R0011_RS4490_, _ami_, _R0011_RS11250_, _metC_, _metA_, and _cfa_); for two genes (_R0011_RS11250_ and _cfa_) after 6 h and finally for genes _metA_ and _cfa_ after 15 h (RER values ranging between 1.790 and 5.721 \(P\) \(<\) 0.05). Meanwhile, after 12 and 24 h, 75% of target genes (_R0011_RS4490_, _ami_, _R0011_RS11250_, _metC_, _metA_, _cfa_, and _fabG_, \(P\) \(<\) 0.005) were under-expressed. (iv) Group 4: Stress and cellular response (G4)  
For strain R0011, the overexpressed genes at 6, 12, and 15 h were _luxS_, _atpD_, _alpC_, and _clpP_ (RER range, 2.248 to 3.392, \(P\) \(<\) 0.05). The gene coding for _atpA_ was repressed at 9 and 24 h in co-culture (Table 1). For strain ATCC 9595, all target genes involved with stress and cellular responses were over-expressed after 12 h of co-culture compared to monoculture (RER range, +3.01 to +17.29, \(P\) \(<\) 0.05). However, at the end of the process (15-24 h), genes _atpA_, _clpP_, _atpD_, _dnaK_, and _groES_ were under-expressed in co-culture (Table 2).