Transcriptome comparison of wild type Azoarcus sp. strain BH72 grown under nitrogen fixation (experiment) with cells grown with combined nitrogen (ammonia) as nitrogen source

Model endophyte Azoarcus sp. BH72 is known to contribute fixed nitrogen to its host Kallar grass by nitrogen fixation and also expresses nitrogenase genes endophytically in rice seedlings in gnotobiotic culture. Availability of fixed nitrogen is one of the important signals regulating the transcription of nitrogenase genes and hence nitrogen fixing activity. Therefore, we analysed global transcription in response to differences in the nitrogen source. Transcription profiles of cells grown microaerobically (0.6% oxygen) on minimal medium with nitrogen (N2-fixing) versus ammonium (combined nitrogen) were compared using a genome-wide microarray approach and differences in the gene expression profile were monitored. RNA from cells grown on nitrogen-free synthetic medium under nitrogen fixation (experiment) and combined nitrogen source as ammonium chloride (control) was used for two-color whole-genome microarray approach.