The distribution of amino acids in seafloor hydrothermal systems was investigated through the determination of the concentrations of total hydrolysable amino acids (THAAs), dissolved free amino acids (DFAAs) and cell density in>200°C black and white smoker fluids sampled from the Mariana Trough. THAA concentrations of>10μM were detected in the black and white smoker fluids, which are higher than those of low temperature (< 53°C) fluids and ambient seawater (< 1μM). 1.4×104-8.6×105cell/ml of microbe was detected from low temperature hydrothermal fluids (< 100°C) and ambient seawater. The concentration of THAAs increased with increasing temperature, although the cell density decreased in high temperature fluid (> 150°C). The bioactivity would be restricted under the high temperature condition.Levels of DFAAs (< 0.7. μM) were very low, suggesting that the amino acids existed mainly as polymers in these hydrothermal fluids. The amino acid polymers plausibly derive from biological protein and dissolve during the reaction of hydrothermal fluids along flow paths around the hydrothermal vents.Amino acids are considered to be unstable under hydrothermal condition (> 200. °C). However, labile amino acids (e.g., Asp and Ser) were abundant in high temperature fluids. These amino acids would be protected by reaction with inorganic compounds. The behavior of the amino acids derived from organisms around hydrothermal vents would be constrained more by abiotic physico-chemical reactions than biological activities in hydrothermal systems.
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