Biotechnological Applications of Extremophilic Microorganisms

Natuschka M. Lee, Natuschka M. Lee

• Verlag: De Gruyter
• Jahr: 2020
• ISBN:
  9783110424362
• Auflage: 1
• Thema: Scienze biologiche
• Thema: Ecologia

This book provides a broad overview how extremophiles can be used in biotechnology, including for the production and degradation of compounds. It reviews various recent discoveries and applications related to a large variety of extremophiles, considering both prokaryotes as well as eukaryotes.

1 Extremophiles: a promising source of novel natural products

Hatti-Kaul Rajni

Abouhmad Adel

1.1 Tapping the potential of extremophiles for diverse bioactive compounds

Extremophiles, the microorganisms inhabiting different extreme environments characterized by high or low temperature, high or low pH, high salt concentration, high pressure, high radiation, etc. or combinations thereof, have developed unique strategies for adapting and thriving in such environments. Studies on extremophiles have been pursued with great interest to determine the mechanisms of adaptation and also as an important source of useful products including enzymes, polymers, compatible solutes, etc. During the last 20–30 years, attention has been directed toward search for novel bioactive compounds produced by extremophiles, which most likely are playing a role in controlling microbial population in the respective ecological niches and are also promising candidates for applications in foods and healthcare. Secondary metabolites produced by microbes have long been a major source of natural products for drug development. Toward the end of the last century, however, high rates of rediscovery of bioactive products from nature prompted a shift to high-throughput screening programs based on molecular targets and combinatorial chemistry, which has unfortunately not led to major discoveries of novel products, and the trend is now to build focused libraries around the chemical scaffolds of natural products. An urgent need for new molecules that could potentially replace the present-day antibiotics, which are becoming ineffective due to the resistance developed by the pathogens, has served as an important driver for the increasing efforts on mining the unexplored ecological niches for bioactive compounds.

The importance of extremophiles, the “non-mesophilic” microorganisms from diverse environments, as a unique source of novel antibacterial, antifungal, and antitumor molecules cannot be overlooked, as evidenced by the increasing number of publications, including reviews and books, especially during the past decade [1–4] and also the number of drugs already developed or under development (primarily from marine sources) [3, 5]. The traditional route of discovering novel products from extremophiles by isolation of microbes and screening for the desired bioactivity has its limitations. Besides missing a major fraction of the unculturable organisms, cultivation of extremophiles under laboratory conditions can be slow and cumbersome due to their extremely slow growth and limited quantities of the active molecules produced for further evaluation. Moreover, the need for extreme environmental conditions required for their growth may require special design or material of the equipment suitable for cultivation. These challenges are now being addressed by the possibility to sequence whole genomes of organisms and metagenomes in an environmental sample as well as bioinformatics and analytical technologies.

The aim of this chapter is to provide a glimpse of the diversity of bioactive molecules produced by extremophilic microorganisms in different environments and also the impact of the latest technological advances on speeding up the discovery process. Environments with extremes of temperature, pH, and salinity are represented in this chapter. The marine habitats are dealt with separately, as they are a combination of high salinity with extreme temperatures and variable acidity and pressure and most importantly have been a source of a larger number of unique metabolites with novel bioactivity than that obtained from terrestrial microorganisms [3].

1.2 Thermophiles

Thermophiles, the microbes inhabiting hot environments, are the group that caught the initial interest of the research community and triggered the exploration of the fascinating area of extremophiles. Thermophilic (growing at temperatures of 50–79°C) and hyperthermophilic (growing at 80°C and above) microbes have been isolated from diverse high-temperature environments around the world like hot springs, volcanoes, deep oil wells, deep sea hydrothermal vents, compost heaps, etc. Eubacteria and Archaea are the common microorganisms found, while fungal and algal species are limited in number in such environments. Thermophiles differ from other microorganisms in having novel structures, such as thermostable enzymes, polysaccharides with repeating branched oligosaccharide units, lipids with isoprenoid chains (with 15, 20, 25, or 40 carbons rather than straight chain) and with ether linked glycerol or polyols, modified polar glyco- and phospholipids, isoprenoid quinones, polyamines and modified nucleosides that play a role in stabilizing DNA, and osmolytes (e.g. mannosylglycerate) for protection of biological macromolecules and cells [1, 6–8]. The primary application of thermophiles in industrial biotechnology has been as an important source of enzymes that could be used in reactions and processes requiring high temperatures, e.g. for DNA amplification in polymerase chain reaction, biomass pretreatment for production of biofuels and chemicals, and biocatalysis for chemical transformations for pharmaceutical and fine chemical industries ...