Issues in the culture of the extremely thermophilic methanogen, methanothermus fervidus

Basic issues in the culture of the extremely thermophilic archaeon, Methanothermus fervidus, have been investigated, including culture medium formulation, substrate yield and product yield coefficient, growth rate and stoichiometry, and H 2 uptake kinetics. The pH optimum for growth of this organism was estimated at 6.9. Growth medium buffered with PIPES instead of bicarbonate supported both increased growth rate and maximum biomass concentration. Substitution of titanium(III) citrate for the reducing agent sodium sulfide improved culture performance as well. However, independent adjustment of iron and nickel concentrations from 11 to 111 μM, respectively, and carbon dioxide partial pressure from 5 to 20 psia did not impact the culture of M. fervidus significantly. An elemental balance approach was utilized to aid in design of a defined medium to support growth to a target maximum biomass concentration of at least 1.0 g dry wt/L. The growth of this organism was limited by H 2 availability in this reformulated culture medium. The maximum growth rate and biomass concentration achieved in anaerobic vials with the defined medium was 0.16 h −1 and 0.74 g dry wt/L, respectively. This maximum biomass concentration was a 72% improvement over that obtained with a literature‐based defined medium. The Monod parameter, K s , with H 2 as limiting substrate, was estimated at 1.1 ± 0.4 psia (55 ± 20 μM in the broth), based on a H 2 consumption study. Representative values for the substrate yield, Y   X/CO   2, and product yield coefficient, Y   CH   4 /X , were determined experimentally to be 1.78 ± 0.04 g dry wt/mol CO 2 , and 0.52 ± 0.01 mol CH 4 /g dry wt, respectively. A bench‐scale fermentation system suitable for the culture of extremely thermophilic anaerobes was designed and constructed and proved effective for the culture of M. fervidus . © 1993 Wiley & Sons, Inc.