PHYSIOLOGY OF THERMOPHILES AND HYPERTHERMOPHILES

Hyperthermophiles?

Hyperthermophiles are microorganisms with the ability to grow optimally at temperatures higher than 80ºC. These amazing creatures inhabit volcanic environments like solfataras, hot springs, deep-sea vents, and geysers.

Some of these microorganisms are able to grow at 113ºC! This is the case of the archaeon Pyrolobus fumarii, the present record holder of thermophily.

Why hyperthermophiles?

The discovery of these exotic beings radically changed our views on biodiversity and posed intriguing questions about structure stability, opening new avenues for research in several areas.

Nearly all hyperthermophiles isolated so far belong to the Domain Archaea, close to the root of the tree of Life, and are believed to represent the most ancient phylogenetic lineages. The elucidation of metabolic strategies in these ancestors of Life on Earth is expected to provide insight into the evolution of metabolic pathways and mechanisms of thermoadaptation.

In order to protect cellular structures from thermal inactivation, hyperthermophiles must have developed strategies of thermostabilisation that, once understood, may be used in many industrial processes such as enzyme-catalysed conversions, often carried out in extreme environmental conditions.

Current research lines

Several years ago our group launched a research project to elucidate biochemical strategies for adaptation of life at high temperature.
Although many enzymes derived from hyperthermophiles are intrinsically heat-stable, this is not a general feature and suggests the presence of extrinsic stabilisation factors, like compatible solutes. In this view, one of these research lines set out to investigate the occurrence and role of compatible solutes in hyperthermophiles.

As a result of this effort, several novel organic solutes have been identified and characterised, and for some of these solutes, like mannosylglycerate (MG) and diglycerolphosphate (DGP), their efficiency as protein protectors was clearly demonstrated, giving rise to two European patents.

These findings made us move into three directions: one is the understanding of the stabilisation phenomenon, using model proteins (like staphylococcal nuclease and D. gigas rubredoxin) to reveal both at the thermodynamic as well as at the molecular level the mechanisms that lead to increased stability. Another aim is the design of new solutes that may have an even greater stabilising ability (solute engineering). This synthesis work is carried out in collaboration with Prof. C. Maycock at ITQB.

The third direction points to the production of these solutes in commercial amounts for industrial applications either by chemical synthesis or using engineered strains.

This goal implies the elucidation of biosynthetic pathways, isolation and characterisation of key-enzymes, optimisation of excretion systems, and development of molecular biology tools for hyperthermophiles.

Another research line aims at the expansion of knowledge of metabolic strategies used in hyperthermophiles with the final goal of exploiting biodiversity for human benefit. In this context, the glycolytic pathways used for sugar metabolism were studied in representative species of hyperthermophilic organisms. As a result novel glycolytic pathways and enzyme activities were discovered in these hyperthermophiles.