Some like it hot - our May/June issue cover story on thermophiles as biotechnological targets

Thermophiles grow best at temperatures higher than 45°C and hyperthermophiles at over 90°C. Thermophilic microorganisms are limited to bacteria and archaea and inhabit a wide range of environments and niches from hydrothermal vents, hot water tanks, compost, volcanic sites and coal refuse to name a few.

Since thermophiles survive on minerals, metals and gases their metabolic processes and enzymes hold promise for industrial, biochemical, biotechnological and other applications.

Thermophiles range from spore forming bacteria such as Bacillus, Clostridia and Moorella species to photosynthetic bacteria including cyanobacteria and green- and purple-sulphur microbes like Chromatium. There are also sulphur oxidisers such as Thiobacillus, sulphate reducers like Desulfovibrio and acidophiles such as Sulfolobus, Metallosphaera and there is Aciduliprofundum boonei which is found in hydrothermal vents featured on TV documentary programmes.

Studying thermophiles using genomic analysis

Image: Castle Geyser erupts with hot water and steam with pools of thermophilic bacteria and it's a cone geyser in the Upper Geyser Basin of Yellowstone National Park, Wyoming, United States. Credit: Benny Marty

What is perhaps most interesting about thermophiles is their physiology and the extreme biochemistry that enables them to tolerate and thrive is such extreme environments. Genomic analysis has been enabled by high-throughput sequencing to analyse these environments and their microbial composition. Only by studying their physiology and growth dynamics can we elucidate their fascinating potential.

Understanding thermophilic growth is key to studying the genomics, biochemistry and physiology of thermophiles.

The molecular mechanisms that enable them to metabolise, grow and tolerate such extreme conditions can help unlock advanced industrial, biochemical and chemical treatments and even in the mining and processing of metals. Their enzymes have been described as potential engineering platforms for the production of fuels and industrial chemicals because of their ability to catalyse industrially significant reactions at high temperatures. Thermostable enzymes produced by thermophiles make promising candidates for advanced industrial, biochemical and biotechnological treatments. Their potential catalytic robustness in extreme conditions is attractive for industrial applications.

Molecular elasticity is a function of catalytic efficiency

Angelo Fontana et al. in Progress in Biotechnology, as far back as 1998 identified that “thermophilic enzymes are usually poor catalysts at room temperature”. Counter-intuitively they found that thermostable enzymes are not rigid molecules at room temperature and this molecular elasticity is a function of catalytic efficiency. According to the paper, an “inverse correlation between enzyme activity and thermostability has been demonstrated in several cases” due to mobility and catalytic potency.

Harnessing and unlocking thermophilic molecular mechanisms can help create recombinant mesophilic hosts for producing those thermophilic enzymes. Since thermophiles survive on minerals, metals and gases their metabolic processes and enzymes hold promise for industrial, biochemical, biotechnological and other applications. We only need to remember the Taq polymerase enzyme used in PCR reactions for example.

Identifying microbes to unlock thermophilic biochemistry

The key to unlocking the benefits of thermophiles and their amazing biochemistry is identifying microbes, characterising them and understanding their relevance.

Having the tools to allow us to isolate and grow these microbial species and communities is key to the beneficial exploitation of microbes. On this journey, a key challenge is identifying methodologies and appropriate devices to grow them and to identify, characterise and understand their physiology. By combining a range of available tools microbes can be identified and characterised, such as with staining, morphology, flow cytometry, and genome sequencing. However, few tools are available for identifying and characterising microbial physiology and measuring their growth and responses to environmental changes and stimuli. This is particularly the case with thermophiles, since their heat loving preferences are not easily compatible with electronic devices!

Growth dynamics data can be a challenge

Obtaining data on growth dynamics allows the characterisation of thermophilic physiology and the optimisation of biotechnological applications. Studying anaerobic physiology, especially of thermophilic anaerobes, is very challenging experimentally. There are not many devices capable of measuring anaerobic and thermophilic growth rates over extended periods with high-resolution data and non-disruptive sampling techniques reproducibly and repeatably.

Growth measurement devices need to provide comparable measurements, reproducibly, obtain high-resolution data and permit standardised methods across devices. Data must be obtained with a high enough resolution to allow for mathematical modelling and statistical analysis. Data must also be obtained over long periods of time for slow growing cultures. Devices need to support different conditions over the growth period and record physiologically significant events at consistently high temperatures. Overall, these are very demanding criteria, and few devices have these capabilities.

Existing laboratory equipment can be used to measure microbial growth, such as spectrophotometers and plate readers, but they have important limitations that make long-term measurement difficult if not impossible under certain conditions. There are, however, dedicated and innovative devices - such as the solution from Humane Technologies - that measure microbial growth for many days at a time. For example, the company’s new device measures continuous thermophilic growth at up to 85?C.

Understanding microbial growth dynamics

Understanding microbial growth dynamics allows the characterisation of microbial physiology and the optimisation of the applications of these microbes and their molecular mechanisms. Studying thermophilic physiology, especially of thermophilic anaerobes, is very challenging experimentally. Using devices capable of measuring thermophilic growth rates over extended periods with high resolution at temperature extremes, that challenge electrical equipment to their limits, is key to studying their physiology.

Evolution has provided rich microbial diversity over millennia. Understanding thermophilic growth is key to studying the genomics, biochemistry and physiology of thermophiles. Only then will it be possible to harvest this microbial diversity and exploit them for new biotechnological, medical, agricultural and other applications.

Author: Tom Graham is Commercial Finance Director for Humane Technologies, a commercial spin-out from the University of Warwick co-founded by Prof Soyer and Dr Sasidharan; humanetechnologies.co.uk