Year-end Sale % OFF 
Abstract
Cyanobacteria are major primary producers in coastal microbial mats and provide biochemical energy, organic carbon, and bound nitrogen to the mat community through oxygenic photosynthesis and dinitrogen fixation. In order to anticipate the specific requirements to optimize their metabolism and growth during a day-and-night cycle, Cyanobacteria possess a unique molecular timing mechanism known as the circadian clock that is well-studied under laboratory conditions but little is known about its function in a natural complex community. Here, we investigated daily rhythmicity of gene expression in a coastal microbial mat community sampled at 6 time points during a 24-h period. In order to identify diel expressed genes, meta-transcriptome data was fitted to periodic functions. Out of 24,035 conserved gene transcript clusters, approximately 7% revealed a significant rhythmic expression pattern. These rhythmic genes were assigned to phototrophic micro-eukaryotes, Cyanobacteria but also to Proteobacteria and Bacteroidetes. Analysis of MG-RAST annotated genes and mRNA recruitment analysis of two cyanobacterial and three proteobacterial microbial mat members confirmed that homologs of the cyanobacterial circadian clock genes were also found in other bacterial members of the microbial mat community. These results suggest that various microbial mat members other than Cyanobacteria have their own molecular clock, which can be entrained by a cocktail of Zeitgebers such as light, temperature or metabolites from neighboring species. Hence, microbial mats can be compared to a complex organism consisting of multiple sub-systems that have to be entrained in a cooperative way such that the corpus functions optimally.
Highlights
Phototrophic microbial mats are highly complex and nearly selfsustaining laminated ecosystems that globally develop amongst others in coastal intertidal sandy sediments
Multiple indications of potential endogenous rhythmicity inducers/ timekeepers in bacterial and archaeal phyla[20,21,27,29] led us to the following fundamental research question: Is rhythmic gene expression in phototrophic microbial mats limited to Cyanobacteria and algae or do other bacteria exhibit a circadian-like, daily rhythmicity? We used meta-transcriptomics and qPCR to analyze diel rhythmicity in gene expression in six microbial mat samples that were taken at regular time points during a 24-h period
Apart from the domain Eukarya, it was thought that only Cyanobacteria possess a circadian clock
Summary
Phototrophic microbial mats are highly complex and nearly selfsustaining laminated ecosystems that globally develop amongst others in coastal intertidal sandy sediments. The presence of kaiBC in both of these Alphaproteobacteria led to higher growth rates and increased fitness under a 24-h light-dark cycle but not under continuous light or dark conditions This KaiBC based system has been proposed to be part of a ‘proto-circadian’ oscillator that does not persist under constant conditions[20] and does not contain other defining circadian characteristics, such as temperature compensation and entrainment.[22] This suggests that organisms possessing only kaiB and/or kaiC are limited to hourglass timekeeping (determination of intervals).[23,24] Potential temperature compensated, endogeneous circadian rhythms in gene expression have been observed in the human gut bacterium Enterobacter aerogenes[25] and may be entrained by its host’s clockdriven signal. The central timekeeper of this circadian oscillator is, hitherto unknown, but it is assumed to be a basic and most ancient circadian timer in all organisms.[27,28] Multiple indications of potential endogenous rhythmicity inducers/ timekeepers in bacterial and archaeal phyla[20,21,27,29] led us to the following fundamental research question: Is rhythmic gene expression in phototrophic microbial mats limited to Cyanobacteria and algae or do other bacteria exhibit a circadian-like, daily rhythmicity? We used meta-transcriptomics and qPCR to analyze diel rhythmicity in gene expression in six microbial mat samples that were taken at regular time points during a 24-h period
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
