Liu, H.

Xiao, X.

Zhao, W.

Open Marine Archive

- 48 - 
 
 
Poly-extreme adaptation of early life in deep ocean: Minimum 
amino acid requirement for hyperthermophilic archaea, 
Thermococcus eurythermalis, under pH boundaries 
Liu Xiaoxia
1
, Zhao Weishu
2
 and Xiao Xiang
2 
1 
Faculty of Bioscience Engineering, Ghent University Coupure Links 653, 9000 Ghent, Belgium 
E-mail: xxliu2@gmail.com 
2 
State Key Laboratory of Microbial Metabolism, Shanghai Jiao Tong University, Dongchuan Road 800, 
Shanghai, China 
 
Thermococcus eurythermalis, a hyperthermophilic archaea isolated deep-sea hydrothermal vents at 
Guaymas basin, has exhibited tolerance to a broad range of different environmental stresses such as 
pH, temperature, salinity, and pressure. The poly-extreme adaptation of the species can potentially 
explain its dominance at its initial habitats, which is characterized by ephemeral and drastic gradient 
change of various chemo-physical factors. While the specific molecular mechanisms of the extreme 
adaptation remained unclear after intensive studies, physiological studies can provide crucial insight of 
the regulation of metabolic pathways under different extreme conditions. Here, we firstly examined the 
minimum amino acid requirement of the archaea under neutral and pH boundary conditions. For the 
experiment, cells were incubated in a defined medium, TRM basal plus each combination of 19 (out of 
20) amino acids, with pH 4.5, pH 7.0, and pH 8.5, respectively. The amino acid was considered 
essential when the lacking of it could significantly affect the cell growth, and the essentiality was 
confirmed by incubation that only had selected amino acids added. Amino acids were used as the only 
carbon and nitrogen source in the medium. The result showed that there are 8 essential amino acids 
(trp, tyr, phe, his, thr, asp, arg, met) for pH 7, and the 12 essential amino acids  (trp, tyr, phe, his, thr, 
asp, arg, lys, val, ile, leu) for both pH 4.5 and pH 8.5 include all the 8 amino acids for optimal 
condition plus four extra ones, three branch-chained (val, ile, leu) and one positively charged (lys). All 
the aromatic amino acids are essential in all the conditions, which might be explained by the easy 
availability of aromatic substances at the oil-immersed habitats. Comparison between these minimum 
amino acid requirements with Miller’s amino acids provided important insight for the Heterotrophic 
Hypothesis regarding the origin of life. 
 
Keywords: extremophiles; deep-ocean; hydrothermal vents; pH; adaptation  


Poly-extreme adaptation of early life in deep ocean: minimum amino acid requirement for hyperthermophilic archaea, <i>Thermococcus eurythermalis</i>, under pH boundaries

Poly-extreme adaptation of early life in deep ocean: minimum amino acid requirement for hyperthermophilic archaea, <i>Thermococcus eurythermalis</i>, under pH boundaries

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