Orthogonal array deciphering MRS medium requirements for isolated Lactobacillus rhamnosus ZY with cell properties characterization

Lactobacillus rhamnosus is a well-known lactic acid bacterium (LAB), but a new ZY strain was isolated for the first time from commercial probiotic powder recently. Although many studies have focused on developing cost-effective media for the production of LAB, the de Man, Rogosa and Sharpe (MRS) medium is still the most common medium for bioprocesses. The aim of the current study is to decipher the composition of MRS based on a statistical approach, which will allow a higher biomass of Lactobacillus to be obtained. In Taguchi's approach, an L₂₇ orthogonal array was adopted to evaluate the significance of 10 ingredients in MRS, in which the effects of the components were ranked according to their effect on biomass at OD₆₀₀ as dextrose > MnSO₄·H₂O > beef extract > CH₃COONa > MgSO₄ > yeast extract > proteose peptone > K₂HPO₄ > ammonium citrate > Tween 80. Although the individual trace elements of ammonium citrate, K₂HPO₄, CH₃COONa and MgSO₄ in MRS had an insignificant influence on the biomass after statistical analysis, the total elimination of trace elements would predominantly affect the cell growth of Lactobacillus. Further characterization of the cell properties through attenuated total reflectance of Fourier transform infrared (ATR-FTIR) spectroscopy and protein identification via SDS-PAGE coupled with tandem mass spectrometry implied that dextrose as major carbon source in MRS played the most crucial role for L. rhamnosus production.