HYDROGEN-TRANSFER BETWEEN METHANOGENS AND FERMENTATIVE HETEROTROPHS IN HYPERTHERMOPHILIC COCULTURES

Interactions involving hydrogen transfer were studied in a coculture o f two hyperthermophilic microorganisms: Thermotoga maritima, an anaero bic heterotroph, and Methanococcus jannaschii, a hydrogenotrophic meth anogen. Cell densities of T. maritima increased 10-fold when coculture d with M. jannaschii at 85 degrees C, and the methanogen was able to g row in the absence of externally supplied H-2 and CO2. The coculture c ould not be established if the two organisms were physically separated by a dialysis membrane, suggesting the importance of spatial proximit y. The significance of spatial proximity was also supported by cell cy tometry, where the methanogen was only found in cell sorts at or above 4.5 mu m in samples of the coculture in exponential phase. An unstruc tured mathematical model was used to compare the influence of hydrogen transport and metabolic properties on mesophilic and hyperthermophili c cocultures. Calculations suggest the increases in methanogenesis rat es with temperature result from greater interactions between the metha nogenic and fermentative organisms, as evidenced by the sharp decline in H-2 concentration in the proximity of a hyperthermophilic methanoge n. The experimental and modeling results presented here illustrate the need to consider the interactions within hyperthermophilic consortia when choosing isolation strategies and evaluating biotransformations a t elevated temperatures. (C) 1997 John Wiley & Sons, Inc.