Transcriptional Profile of Lactobacillus helveticus grown in milk vs. MRS medium

L. helveticus is used to modulate cheese flavor and as a starter organism in certain cheese varieties. Our group has compiled a draft (4x) sequence for the 2.4 Mb genome of an industrial strain L. helveticus CNRZ32. The primary aim was to investigate expression of 168 completely sequenced genes during growth in milk and MRS medium using microarrays. Oligonucleotide probes against each of the completely sequenced genes were compiled on maskless photolithography-based DNA microarrays. Additionally, the entire draft genome sequence was used to produce tiled microarrays where the non-interrupted sequence contigs were covered by consecutive 24-mer probes. Keywords: growth conditions response Milk and MRS cultures were incubated at 42oC until cells reached mid-log phase. Three independent growth experiments in milk and MRS were done; two identical samples were taken from each culture and used for the RNA isolation. A total of six RNA samples for each growth condition were used to independently produce labeled cDNA for microarray experiments.