Physiological, metabolic and biotechnological features of extremely thermophilic microorganisms

Abstract

The current upper thermal limit for life as we know it is approximately 120°C. Microorganisms that grow optimally at temperatures of 75°C and above are usually referred to as ‘extreme thermophiles’ and include both bacteria and archaea. For over a century, there has been great scientific curiosity in the basic tenets that support life in thermal biotopes on earth and potentially on other solar bodies. Extreme thermophiles can be aerobes, anaerobes, autotrophs, heterotrophs, or chemolithotrophs, and are found in diverse environments including shallow marine fissures, deep sea hydrothermal vents, terrestrial hot springs – basically, anywhere there is hot water. Initial efforts to study extreme thermophiles faced challenges with their isolation from difficult to access locales, problems with their cultivation in laboratories, and lack of molecular tools. Fortunately, because of their relatively small genomes, many extreme thermophiles were among the first organisms to be sequenced, thereby opening up the application of systems biology-based methods to probe their unique physiological, metabolic and biotechnological features. The bacterial genera Caldicellulosiruptor, Thermotoga and Thermus, and the archaea belonging to the orders Thermococcales and Sulfolobales, are among the most studied extreme thermophiles to date. The recent emergence of genetic tools for many of these organisms provides the opportunity to move beyond basic discovery and manipulation to biotechnologically relevant applications of metabolic engineering.

Correlating enzyme annotations with a large set of microbial growth temperatures reveals metabolic adaptations to growth at diverse temperatures

“…Metabolism varies widely among thermophiles and general trends are hard to discern as it is extremely difficult to distinguish between the effect of speciation versus adjustment to extreme environments. For example, three main glycolytic pathways are used by bacteria in general: the traditional Embden-Meyerhof (EM) glycolysis, the Entner-Doudoroff pathway, and the pentose phosphate pathway; all three can also be found in different thermophilic bacteria [ 20 – 23 ]. In archaea, however, only modified variants of classical sugar degradation pathways were identified [ 23 , 24 ].…”

Correlating enzyme annotations with a large set of microbial growth temperatures reveals metabolic adaptations to growth at diverse temperatures

“…Metabolism varies widely among thermophiles and general trends are hard to discern as it is extremely difficult to distinguish between the effect of speciation versus adjustment to extreme environments. For example, three main glycolytic pathways are used by bacteria in general: the traditional Embden-Meyerhof (EM) glycolysis, the Entner-Doudoroff pathway, and the pentose phosphate pathway; all three can also be found in different thermophilic bacteria (Counts et al 2017;Swarup et al 2014;Brumm et al 2015;Selig et al 1997) . In archaea, how ever, only modified variants of classical sugar degradation pathways were identified (Brasen et al 2014;Selig et al 1997) .…”

13C metabolic flux analysis of three divergent extremely thermophilic bacteria: Geobacillus sp. LC300, Thermus thermophilus HB8, and Rhodothermus marinus DSM 4252

“…Research on extremely thermophilic organisms has intensified in the past two decades, driven by technological advances in whole-genome sequencing, genetic tool development, and other breakthroughs in omics sciences (Counts et al, 2017). Given the unique physiological and metabolic features of thermophiles, they are increasingly investigated for their biotechnological potential in areas such as bioremediation (Feng et al, 2007), as a source of thermostable enzymes (Elleuche et al, 2014; Canakci et al, 2012; Ezeji and Bahl, 2006; Verma et al, 2013), and as novel platforms for the production of biofuels and chemicals from renewable feedstocks (Taylor et al, 2009; Chang and Yao, 2011).…”