Effect of carbon and nitrogen sources on growth dynamics and exopolysaccharide production for the hyperthermophilic archaeon Thermococcus litoralis and bacterium Thermotoga maritima

Batch and continuous cultures were used to compare specific physiological f eatures of the hyperthermophilic archaeon, Thermococcus litoralis (T-opt of 85 degrees to 88 degrees C), to another fermentative hyperthermophile that reduces S degrees facultatively, that is, the bacterium Thermotoga maritim e (T-opt of 80 degrees to 85 degrees C). Under nutritionally optimal condit ions, these two hyperthermophiles had similar growth yields on maltose and similar cell formula weights based on elemental analysis: CH1.7O0.7N0.2S0.0 06 for T. litoralis and CH1.6O0.6N0.2S0.005 for T. maritima. However, they differed with respect to nitrogen source, fermentation product patterns, an d propensity to form exopolysaccharides (EPS). T. litoralis could be cultur ed in the absence or presence of maltose on an amino acid-containing define d medium in which amino acids served as the sole nitrogen source. T. mariti ma, on the other hand, did not utilize amino acids as carbon, energy, or ni trogen sources, and could be grown in a similar defined medium only when su pplemented with maltose and ammonium chloride. Not only was T. litoralis un able to utilize NH4Cl as a nitrogen source; its growth was inhibited at cer tain levels. At 1 g/L (-20 mM) NH4Cl, the maximum growth yield (Y-X/Smax) f or T. litoralis was reduced to 13 g cells dry weight (CDW)/mol glucose from 40 g CDW/mol glucose in media lacking NH4Cl. Alanine production increased with increasing NH4Cl concentrations and was most pronounced if growth on N H4Cl was carried out in an 80% H-2 atmosphere. In T. maritima cultures, whi ch would not grow in an 80% H, atmosphere, alanine and EPS were produced at much lower levels, which did not change with NH4Cl concentration. EPS prod uction rose sharply at high dilution rates for both organisms, such that ma ltose utilization plots were biphasic. Wall growth effects were also noted, because cultures failed to wash out at dilution rates significantly above maximum growth rates determined from batch growth experiments. This study i llustrates the importance of effective cultivation methods for addressing p hysiological issues related to the growth of hyperthermophilic heterotrophs . (C) 2000 John Wiley & Sons, Inc.