화학공학소재연구정보센터
Biotechnology and Bioengineering, Vol.69, No.5, 537-547, 2000
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 features 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 maritime (T-opt of 80 degrees to 85 degrees C). Under nutritionally optimal conditions, these two hyperthermophiles had similar growth yields on maltose and similar cell formula weights based on elemental analysis: CH1.7O0.7N0.2S0.006 for T. litoralis and CH1.6O0.6N0.2S0.005 for T. maritima. However, they differed with respect to nitrogen source, fermentation product patterns, and propensity to form exopolysaccharides (EPS). T. litoralis could be cultured in the absence or presence of maltose on an amino acid-containing defined medium in which amino acids served as the sole nitrogen source. T. maritima, on the other hand, did not utilize amino acids as carbon, energy, or nitrogen sources, and could be grown in a similar defined medium only when supplemented with maltose and ammonium chloride. Not only was T. litoralis unable to utilize NH4Cl as a nitrogen source; its growth was inhibited at certain levels. At 1 g/L (-20 mM) NH4Cl, the maximum growth yield (Y-X/Smax) for 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 NH4Cl was carried out in an 80% H-2 atmosphere. In T. maritima cultures, which 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 production rose sharply at high dilution rates for both organisms, such that maltose 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 illustrates the importance of effective cultivation methods for addressing physiological issues related to the growth of hyperthermophilic heterotrophs.