Enzymology in perchlorate rich, multi-extreme environments

Abstract

The potential for life on Mars is one of the most interesting and yet elusive questions in modern science. The surface of Mars holds little prospect for biology due to the large daily temperature ranges, ionizing radiation, the presence of deleterious salts and the absence of liquid water, besides many other contributing factors. However, deep beneath the surface of Mars we may find environments which, while extreme in their own right, are free from some of the more destructive factors experienced on the Martian surface.

The deep subsurface of Mars may hold liquid water environments, which would experience high environmental pressures due to their subterranean nature, while also experiencing extremely low temperatures, perhaps as low as -70 °C. In order for such an aqueous environment to remain liquid at such low temperatures, it would require the presence of saturating concentrations of perchlorate salts which have the ability to lower the freezing of water to temperatures around -80 °C. Such an environment provides us with three parameters, perchlorates, pressure, and temperature, against which we can determine the potential for proteinaceous biochemistry to exist in such an extreme environment. How each of these individual factors affect proteinaceous biochemistry is relatively well understood, but we know practically nothing about how these factors interact in combination to ultimately affect biochemistry in such a multi-extreme environment. This is explored throughout this thesis by investigating the effects of perchlorate salts, high pressures, and low temperatures on the activity and stability of the model enzyme α-chymotrypsin. Additionally a meta-analysis of cold adapted enzymes was conducted in order to facilitate a better understanding of the fundamental adaptations which allows enzymes to become more active at low temperatures. Through this research, I found that while perchlorate salts lower the enzyme activity of α-chymotrypsin, high pressures can rescue this lost activity. Furthermore, the perchlorate induced loss of enzyme activity is found to be temperature dependent, as I have shown that perchlorate salts can increase the activity of α-chymotrypsin at low temperatures. These results suggest that while perchlorate rich environments are generally deleterious towards proteinaceous biochemistry and life, the high pressures of deep subsurface environments may counteract some of the negative perchlorate effects, and that the perchlorate salts themselves may actually facilitate increased biochemical potential at low environmental temperatures.

While this data does not suggest that perchlorate rich environments are necessarily habitable or inhabited, it does provide us with a mechanistic understanding of how biochemical adaptations could advantageously use physical parameters such as temperature and pressure in order to increase biomolecular perchlorate tolerance.