The present invention relates to methods for monitoring differential expression of a plurality of genes in a first Bacillus cell relative to expression of the same genes in one or more second Bacillus cells using microarrays containing Bacillus genomic sequenced tags. The present invention also relates to computer readable media and computer-based systems. The present invention further relates to substrates containing an array of Bacillus licheniformis or Bacillus clausii GSTs.