Trimethylamine N-Oxide (TMAO) and Trimethylamine (TMA) Determinations of Two Hadal Amphipods

Abstract

Hadal trenches are a unique habitat with high hydrostatic pressure, low temperature and scarce food supplies. Amphipods are the dominant scavenging metazoan species in this ecosystem. Trimethylamine (TMA) and trimethylamine oxide (TMAO) have been shown to play important roles in regulating osmotic pressure in mammals, hadal dwellers and even microbes. However, the distributions of TMAO and TMA concentrations of hadal animals among different tissues have not been reported so far. Here, the TMAO and TMA contents of eight tissues of two hadal amphipods, Hirondellea gigas and Alicella gigantea from the Mariana Trench and the New Britain Trench, were detected by using the ultrahigh performance liquid chromatography–mass spectrometry (UPLC-MS/MS) method. Compared with the shallow water Decapoda, Penaeus vannamei, the hadal amphipods possessed significantly higher TMAO concentrations and a similar level of TMA in all the detected tissues. A higher level of TMAO was detected in the external organs (such as the eye and exoskeleton) for both of the two hadal amphipods, which indicated that the TMAO concentration was not evenly distributed, although the same hydrostatic pressure existed in the outer and internal organs. Moreover, a strong positive correlation was found between the concentrations of TMAO and TMA in the two hadal amphipods. In addition, evolutionary analysis regarding FMO3, the enzyme to convert TMA into TMAO, was also conducted. Three positive selected sites in the conserved region and two specific mutation sites in two conserved motifs were found in the A. gigantea FMO3 gene. Combined together, this study supports the important role of TMAO for the environmental adaptability of hadal amphipods and speculates on the molecular evolution and protein structure of FMO3 in hadal species.

Morphological and molecular evolution of hadal amphipod’s eggs provides insights into embryogenesis under high hydrostatic pressure

“…The TMAO content was much higher in the eggs of A. gigantea than crustaceans inhabiting shallow waters, while there was no significant difference in TMA contents ( Figure 5 ). These results are similar to those of previous studies that TMAO concentrations are significantly higher in hadal amphipods with similar levels of TMA among different tissues ( Liu et al, 2022 ). TMAO is produced by the oxidation of TMA under the action of the flavin monooxygenases (FMOs) ( Canyelles et al, 2018 ), while TMA is mainly formed by the consumption of carnitine choline by gut microorganisms ( Wang et al, 2011 ).…”

“…Previous studies have reported that TMAO concentrations are significantly higher in the tissues of hadal species than shallow-water species ( Gillett et al, 1997 ; Samerotte et al, 2007 ; Liu et al, 2022 ). Likewise, the results of the present study revealed that TMAO contents were significantly higher in the eggs of hadal amphipods than those of shallow-water crustaceans, while TMA concentrations were similar ( Figure 5 ).…”

“…TMAO plays important roles in the regulation of osmotic pressure in mammals, hadal zone dwellers, and even microbes ( Yancey et al, 2014 ; Qin et al, 2021 ; Liu et al, 2022 ). The TMAO content was much higher in the eggs of A. gigantea than crustaceans inhabiting shallow waters, while there was no significant difference in TMA contents ( Figure 5 ).…”

“…The egg suspension was ultrasonicated three times in an ice bath, then chilled to −20°C for 20 min and centrifuged at 13,000 rpm and 4°C for 10 min. The supernatant was collected, diluted by 20 fold, and 400-ml aliquots were stored at 4°C until analysis of the TMAO and TMA concentrations by ultra-performance liquid chromatography–tandem mass spectrometry (Waters Corporation, Milford, MA, United States), as described by Liu et al (2022) .…”

“…For example, trimethylamine oxide (TMAO) is an important osmotic regulator produced by oxidation of trimethylamine (TMA) via flavin-dependent monooxygenases (FMOs) ( Canyelles et al, 2018 ). The concentration of TMAO is reported to gradually increase with depth, suggesting an important function for organisms occupying hadal zones ( Yancey et al, 2014 ; Qin et al, 2021 ; Liu et al, 2022 ). The ability of amphipods to thrive in such extreme habitats and embryogenesis of hadal-dwelling amphipods have attracted much interest.…”