Transcriptional analysis of nitrogen fixation inPaenibacillus durusduring growth in nitrogen-enriched medium

Abstract

AbstractPaenibacillus durusstrain ATCC 35681Tis a Gram-positive diazotroph that displayed capability of fixing nitrogen even in the presence of nitrate or ammonium. However, the nitrogen fixation activity was detected only at day 1 of growth when cultured in liquid nitrogen-enriched medium. The transcripts of all thenifHhomologues were present throughout the 9-day study. When grown in nitrogen-deficient medium, nitrogenase activities occurred from day 1 until day 6 and thenifHtranscripts were also present during the course of the study albeit at different levels. In both studies, the absence of nitrogen fixation activity regardless of the presence of thenifHtranscripts raised the possibility of a post-transcriptional or post-translational regulation of the system. A putative SigA box sequence was found upstream of the transcription start site ofnifB1, the first gene in the major nitrogen fixation cluster. The upstream region ofnifB2showed a promoter recognisable by SigE, a sigma factor normally involved in sporulation.Significance and Impact of the StudyPaenibacillus durusstrain ATCC 35681Tis a nitrogen fixing Gram positive bacterium with an unconventional physiological characteristic of being able to fix nitrogen even in the presence of either nitrate or ammonium. It has a total of 6nifHhomologues in its genome. In this study, we analysed the transcriptional levels of thenifHhomologues when grown under nitrogen-enriched and nitrogen-depleted medium. Under nitrogen-enriched condition, the nitrogen fixation activity was detected only at day 1 of growth but the transcripts of all thenifHhomologues were detected during the course of the study from day 1 until day 9. In nitrogen-deficient condition, nitrogen fixation activities were recorded from day 1 until day 6 and thenifHtranscripts were present throughout the study. The absence of nitrogen fixation activity even in the presence of thenifHtranscripts raised the possibility of a post-transcriptional or post-translational regulation of the system.