1-18: Draft genome sequence reveals insights into the H2 metabolism of Caloramator celere

Caloramator celere (former Thermobrachium celere) is an anaerobic alkalithermophilic bacterium able to covert sugars to H₂, CO₂, acetate, ethanol and formate. Thanks to its ability to rapidly grow in an extremely selective environment (doubling time=10 min; T_opt=67°C; pH_{67°C opt}=8.2) it might be a promising candidate for biohydrogen production in open (non-sterile) systems.

The whole genome of C. celere was recently sequenced generating a draft genome sequence consisting of 43 scaffolds with a total assembly size of 2.32 Mb (G+C content of 31%) and containing 2260 coding sequences.

Bioinformatic analyses revealed genes encoding key enzymes involved in pyruvate catabolism pathways. At pyruvate node one putative pyruvate:formate lysase (potentally activated by three putative pyruvate:formate

lyase activating enzymes) and two putative pyruvate:ferredoxin oxidoreductases catalyze the conversion of pyruvate to acetyl-CoA. Two putative NADH-dependent FeFe-hydrogenases and one putative ferredoxin-dependent membrane bound NiFe-hydrogenase are involved in the regeneration of NAD⁺ and oxidized ferredoxin through proton reduction with consequent H₂ synthesis.  Alternatively, regeneration of NAD⁺ can be carried out by conversion of acetyl-CoA to ethanol by two putative alcohol dehydrogenases.

Experimental results showed that carbon and electron flow distributions were affected by the feedback inhibition caused by H₂ accumulation. When the P_H2 was kept under 23 kPa by nitrogen sparging of culture headspace H₂ production by C. celere yielded 3.53 mol-H₂/mol-glucose with a remarkable maximum H₂ production rate of 41.5 mmol-H₂/l/h.

Genetic information, together with experimental data, outlined the possible metabolic scenario for H₂ synthesis, highlighting potential process improvements to enhance H₂ production from C. celere.