Abstract
Parageobacillus thermoglucosidasius is a metabolically versatile, facultatively anaerobic thermophile belonging to the family Bacillaceae. Previous studies have shown that this bacterium harbours co-localised genes coding for a carbon monoxide (CO) dehydrogenase (CODH) and Ni-Fe hydrogenase (Phc) complex and oxidises CO and produces hydrogen (H2) gas via the water-gas shift (WGS) reaction. To elucidate the genetic events culminating in the WGS reaction, P. thermoglucosidasius DSM 6285 was cultivated under an initial gas atmosphere of 50% CO and 50% air and total RNA was extracted at ~8 (aerobic phase), 20 (anaerobic phase), 27 and 44 (early and late hydrogenogenic phases) hours post inoculation. The rRNA-depleted fraction was sequenced using Illumina NextSeq, v2.5, 1x75bp chemistry. Differential expression revealed that at 8 vs.. 20, 20 vs.. 27 and 27 vs.. 44 h post inoculation, 2190, 2118 and 231 transcripts were differentially (FDR < 0.05) expressed. Cluster analysis revealed 26 distinct gene expression trajectories across the four time points. Of these, two similar clusters, showing overexpression at 20 relative to 8 h and depletion at 27 and 44 h, harboured the CODH and Phc transcripts, suggesting possible regulation by O2. The transition between aerobic respiration and anaerobic growth was marked by initial metabolic deterioration, as reflected by up-regulation of transcripts linked to sporulation and down-regulation of transcripts linked to flagellar assembly and metabolism. However, the transcriptome and growth profiles revealed the reversal of this trend during the hydrogenogenic phase.
Highlights
Hydrogen gas (H2) has the highest energy per unit mass of all fuels [1]
These results suggest that the transcriptome datasets are sufficiently robust to validly assess transcript dynamics across the studied conditions
RNA-seq based transcriptome profiling of the facultative anaerobe P. thermoglucosidasius DSM 6285 growing under an initial gas atmosphere of 50% air and 50% carbon monoxide (CO) revealed a metabolic flexibility reflective of its ability to switch between aerobic growth, anaerobic survival, and anaerobic growth to recovery via the Water Gas Shift (WGS) reaction
Summary
Hydrogen gas (H2) has the highest energy per unit mass of all fuels (heating value of 141.9 MJ/kg) [1]. In contrast to traditional fuels, H2 is a zero-emission fuel when undergoing complete combustion in the presence of oxygen (2 H2 + O2 → 2 H2O) [2] As such H2 has become prominent as a clean and sustainable alternative energy source [3]. Biohydrogen is principally generated via biophotolysis of water by algae, and bacterial photo-fermentation and dark fermentation of organic substances [6]. These methods are constrained by both economic and technological limitations, including high costs of production and low yields [5]. A broad range of taxa including mesophilic anaerobes such as Rhodospirillum rubrum and Rhodopseudomonas palustris [7], thermophilic anaerobes such as Carboxydothermus hydrogenoformans, C. pertinax and Thermosinus carboxydivorans [8,9], and thermophilic archaea such as Thermococcus onnurineus [10] have been shown to tolerate high concentration of CO and oxidise this substrate via the WGS reaction [8,11]
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