With an average depth of approximately 3850 m of the deep-sea biosphere, the organisms living in the benthic domain are subjected to an average pressure of ca. 390 atmospheres. It is therefore important to test the effect of pressure on some specic variables. Microbial communities in the deep-sea sediments may include both autochthonous species adapted to in situ temperature and pressure, and allochthonous taxa attached to settling particles. The activity of allochthonous microbes can also change with depth (Turley et al. 1995; Tamburini et al. 2006) as a result of highpressure conditions. Thus, microbial activity measured at both atmospheric and in situ deep-sea conditions may reect different components of the microbial physiological status (Eardly et al. 2001; Tamburini 2006; Deming 2007).