Project description:Trans-encoded sRNA154 is exclusively expressed under nitrogen (N)-deficiency in Methanosarcina mazei strain Gö1. The respective deletion strain showed a significant growth defect under N-limitation, pointing towards a regulatory role of sRNA154 in the N-metabolism. Aiming to elucidate this regulatory function we characterized sRNA154 by biochemical and genetic approaches. 24 homologs of sRNA154 were identified in recently reported draft genomes of Methanosarcina strains, demonstrating high conservation in sequence and predicted secondary structure with two highly conserved single stranded loop regions. In silico target prediction uncovered multiple potential interactions of both conserved loops with mRNA targets 5´untranslated region and coding sequence) encoding key components of the N-metabolism. In line with the computational prediction transcriptome studies of the sRNA154 deletion mutant by an RNA-seq approach uncovered nrpA-mRNA as a potential target, encoding the transcriptional activator of the nitrogen fixation (nif)-operon. Further evidence obtained by electromobility shift-, stability- and complementation assays, strongly argues for a stabilizing effect of sRNA154 on nrpA-mRNA by binding with both loops. Studying the further predicted N-related targets showing lower transcript levels in the absence of sRNA154, demonstrated that nifH transcript levels are most likely indirectly affected by sRNA154 due to enhanced stability of the nrpA transcripts. Besides, translation of glnA2-mRNA, encoding glutamine synthetase, appears to be affected by sRNA154 masking the ribosome binding site (RBS), whereas glnA1-mRNA appears to be stabilized by sRNA154. Overall, we propose that sRNA154 has a crucial role in N-metabolism in M. mazei and allows a feed forward regulation of nif-gene expression by stabilizing nrpA mRNA.
Project description:Methylotrophic methanogenesis predominates at low temperatures in the cold Zoige wetland in Tibet. To elucidate the basis of cold-adapted methanogenesis in these habitats, Methanosarcina mazei zm-15 was isolated, and the molecular basis of its cold activity was studied. For this strain, aceticlastic methanogenesis was reduced 7.7-fold during growth at 15°C versus 30°C. Methanol-derived methanogenesis decreased only 3-fold under the same conditions, suggesting that it is more cold adaptive. Reverse transcription-quantitative PCR (RT-qPCR) detected <2-fold difference in the transcript abundances of mtaA1, mtaB1, and mtaC1, the methanol methyltransferase (Mta) genes, in 30°C versus 15°C culture, while ackA and pta mRNAs, encoding acetate kinase (Ack) and phosphotransacetylase (Pta) in aceticlastic methanogenesis, were 4.5- and 6.8-fold higher in 30°C culture than in 15°C culture. The in vivo half-lives of mtaA1 and mtaC1B1 mRNAs were similar in 30°C and 15°C cultures. However, the pta-ackA mRNA half-life was significantly reduced in 15°C culture compared to 30°C culture. Using circularized RNA RT-PCR, large 5' untranslated regions (UTRs) (270 nucleotides [nt] and 238 nt) were identified for mtaA1 and mtaC1B1 mRNAs, while only a 27-nt 5' UTR was present in the pta-ackA transcript. Removal of the 5' UTRs significantly reduced the in vitro half-lives of mtaA1 and mtaC1B1 mRNAs. Remarkably, fusion of the mtaA1 or mtaC1B1 5' UTRs to pta-ackA mRNA increased its in vitro half-life at both 30°C and 15°C. These results demonstrate that the large 5' UTRs significantly enhance the stability of the mRNAs involved in methanol-derived methanogenesis in the cold-adaptive M. mazei zm-15.