1. Pressure Adaptations

High pressure traps water molecules at a high density around charged molecules, interfering with critical binding events in cells involving proteins. Dr. Joe Siebenaller of L.S.U. and other researchers have found that many proteins in deep-sea fishes somehow compensate for this effect. However, not all deep-sea proteins are pressure resistant. Pressure also makes membranes more rigid, impairing transport functions, etc. Researchers have found that deep-sea organisms have unsaturated lipids in their membranes to "loosen" them up. Unsaturated lipids (an example is vegetable oil) have mixed C-C single bonds and C=C double-bonds that prevent the lipid chains from stacking tightly together, making the lipid or fat more liquidy. In contrast, saturated lipids have all C-C single bonds that stack together, making the lipid or fat more rigid (an example is butter).

In my laboratory, we have found that deep-sea fishes and some invertebrates have the highest known levels of trimethylamine oxide or TMAO (see below). This is a common compound in many marine animals, used to help maintain water balance against the high salinity of the sea. If your computer had "RealOdor" or "QuickSmell" technology, you'd recognize TMAO--it and its breakdown product, TMA, are what makes marine animals smell fishy. TMAO is also a stabilizer of proteins (helping these biological molecules remain functional when perturbed), and we have extensive evidence (see example below) that it may be very high in these animals in order to help pressure-sensitive proteins overcome pressure inhibition (perhaps by helping to remove dense water from charged molecules). See references by Gillett, Kelly, Yancey below, and New Scientist news story (1999).

Recently, we analyzed deep clams from cold seeps and found they have an unusual compound first reported by Alberic and Boulegue in 1990: serine-phosphoethanolamine-X (where X is an unknown). We discovered that this compound increases with depth in clams from 1100 to 6400m depth. It may help protect proteins from pressure effects (Fiess et al.).

2. Sulfide Adaptations

We are also investigating the roles of unusual sulfur osmolytes in animals from hydrothermal vents and gas seeps. Researchers in France (Alberic, Pranal, Pruski, Fiala-Medioni and others) found these animals to have large amounts of hypotaurine and thiotaurine, rare compounds related to the very common marine osmolyte taurine. [Taurine is also crucial for mammalian brain development and is a major ingredient in many sports/energy drinks.] These all contain sulfur, and may help in transporting sulfides to the bacterial symbiotes that these animals rely on (see Vents/Seeps page), or may protect the animals from toxic sulfide.

Recently we found that snails and limpets, as well as the heat-loving paralvinellid worms, from the Juan de Fuca Ridge vents contain hypotaurine and thiotaurine at high levels even though they don't have internal symbionts. We have also found that animals (with or without symbionts) exposed to the highest sulfide levels have highest levels of hypotaurine and thiotaurine (Rosenberg et al. 2006; Brand et al. 2007; Yancey et al. 2009).

We discovered the sulfur compound methyltaurine as a dominant osmolyte in Lamellibrachia seep tubeworms. Its function is unknown, but as a methylamine, it may help counteract pressure effects (Yin et al. 2000).

3. Protein Contents and Anatomy of Midwater (Mesopelagic) Fishes (1980s)

We discovered that the muscles of midwater fishes (such as viperfish) have extremely low protein contents: 5-10% protein, compared to 15-20% in a surface (epipelagic fish, such as a tuna). We also discovered that some of these deep fish have an unusual buoyant gelatinous layer around their spines or under their skins:

• Siebenaller, J.F., P.H. Yancey (1984). The protein composition of white skeletal muscle from mesopelagic fishes having different water and protein contents. Mar. Biol. 78: 129-137
• Yancey, P.H., R. Lawrence-Berrey, M. D. Douglas (1989). Adaptations in mesopelagic fishes. I. Buoyant glycosaminoglycan layers in species without diel vertical migrations. Mar. Biol. 103: 453-459
• Yancey, P.H., T. Kulongoski, M.D. Usibelli, R. Lawrence-Berrey, A. Pedersen (1992). Adaptations in mesopelagic fishes. II. Protein contents of various muscles and actomyosin contents and structure of swimming muscle. Comp. Biochem. Physiol. 103B: 691-6
  

See also Midwater page for pictures of the gelatinous layer and fishes.

References for this section.

Next:  The Oceans in Trouble   ....