G. Bretler et Iw. Marison, A MEDIUM OPTIMIZATION STRATEGY FOR IMPROVEMENT OF GROWTH AND METHANE PRODUCTION BY METHANOBACTERIUM-THERMOAUTOTROPHICUM, Journal of biotechnology, 50(2-3), 1996, pp. 201-212
Methanobacterium thermoautotrophicum, strain Hveragerdi, has been cult
ivated in a completely defined mineral salts medium, under strictly an
aerobic conditions with CO2 and H-2 as sole carbon and energy source,
respectively. During optimization of the medium an iron limitation was
identified that could not be overcome by the simple addition of iron-
-or iron complexed with nitrilotriacetate (NTA)--to the medium, due to
the formation of insoluble FeS complexes. In order to define a medium
optimization strategy, and to avoid laborious empirical optimization
procedures, a theoretical model has been developed in order to describ
e the solubility of iron and other mineral species in the medium as a
function of the concentration of sulfur and NTA. This model may be app
lied for the optimization of any medium component. With this informati
on sulfide has been replaced by a combination of cysteine and thiosulp
hate in conjunction with a non-toxic reducing agent (titanium (III) ci
trate). Using this defined medium precipitation was avoided and an iro
n limitation was overcome resulting in a 5-fold improvement of the fin
al biomass concentration from 2-3 g l(-1) to 11.2 g l(-1) together wit
h a 2-fold increase (from 45 to almost 100%) in the conversion of CO2
and H-2 to CH4, even at gas flow rates as high as 6 1 min(-1).