Pressure adaptation is linked to thermal adaptation in salt-saturated marine habitats

The present study provides a deeper view of protein

functionality as a function of temperature, salt and

pressure in deep-sea habitats. A set of eight different

enzymes from five distinct deep-sea (3040–4908 m

depth), moderately warm (14.0–16.5°C) biotopes,

characterized by a wide range of salinities (39–348

practical salinity units), were investigated for this

purpose. An enzyme from a ‘superficial’ marine

hydrothermal habitat (65°C) was isolated and charac-

terized for comparative purposes. We report here the

first experimental evidence suggesting that in salt-

saturated deep-sea habitats, the adaptation to high

pressure is linked to high thermal resistance (

P

value

=

0.0036). Salinity might therefore increase the

temperature window for enzyme activity, and possibly

microbial growth, in deep-sea habitats. As an

example, Lake

Medee

, the largest hypersaline deep-

sea anoxic lake of the Eastern Mediterranean Sea,

where the water temperature is never higher than

16°C, was shown to contain halopiezophilic-like

enzymes that are most active at 70°C and with dena-

turing temperatures of 71.4°C. The determination of

the crystal structures of five proteins revealed

unknown molecular mechanisms involved in protein

adaptation to poly-extremes as well as distinct active

site architectures and substrate preferences relative

to other structurally characterized enzymes