Thermotoga maritima

Thermotoga maritima is a hyperthermophilic, anaerobic organism that is a member of the order Thermotogales. It employs [FeFe]-hydrogenases to produce hydrogen gas (H2) by fermenting many different types of carbohydrates.[1]

Thermotoga maritima
Outline of a Thermotoga maritima section showing the "toga"
Scientific classification
Domain:
Bacteria
Phylum:
Thermotogae
Class:
Thermotogae
Order:
Thermotogales
Family:
Thermotogaceae
Genus:
Thermotoga
Species:
T. maritima
Binomial name
Thermotoga maritima
Huber et al., 1986

History

First discovered in the sediment of a marine geothermal area near Vulcano, Italy, Thermotoga maritima resides in hot springs as well as hydrothermal vents.[2] The ideal environment for the organism is a water temperature of 80 °C (176 °F), though it is capable of growing in waters of 55–90 °C (131–194 °F).[3] Thermotoga maritima is the only bacterium known to grow at this high a temperature; the only other organisms known to live in environments this extreme are members of the domain Archaea. The hyperthermophilic abilities of T. maritima, along with its deep lineage, suggests that it is potentially a very ancient organism.[4]

Physical attributes

T. maritima is a non-sporulating, rod shaped, gram-negative bacterium.[5] When viewed under a microscope, it can be seen to be encased in a sheath-like envelope which resembles a toga, hence the "toga" in its name.[5]

Metabolism

As an anaerobic fermentative chemoorganotrophic organism, T. maritima catabolizes sugars and polymers and produces carbon dioxide (CO2) and hydrogen (H2) gas as by-products of fermentation.[5] T. maritima is also capable of metabolizing cellulose as well as xylan, yielding H2 that could potentially be utilized as an alternative energy source to fossil fuels.[6] Additionally, this species of bacteria is able to reduce Fe(III) to produce energy using anaerobic respiration. Various flavoproteins and iron-sulphur proteins have been identified as potential electron carriers for use during cellular respiration.[6] However, when growing with sulfur as the final electron acceptor, no ATP is produced. Instead, this process eliminates inhibitory H2 produced from fermentative growth.[6] Collectively, these attributes indicate that T. maritima has become resourceful and capable of metabolizing a host of substances in order to carry out its life processes.

Hydrogenase Activity

Hydrogenases are metalloenzymes that catalyze the reversible hydrogen conversion reaction: H2 ⇄ 2 H++ 2 e−. A Group C [FeFe]-hydrogenase from Thermotoga maritima (TmHydS) has showed modest hydrogen conversion activity and reduced sensitivity to the enzyme's inhibitor, CO, in comparison to Group A prototypical and bifurcating [FeFe]-hydrogenases.[7] The TmHydS has a hydrogenase domain with distinct amino acid modifications in the active site pocket, including the presence of a Per-Arnt-Sim (PAS) domain.

Genomic composition

The genome of T. maritima consists of a single circular 1.8 megabase chromosome encoding for 1877 proteins.[8] Within its genome it has several heat and cold shock proteins that are most likely involved in metabolic regulation and response to environmental temperature changes.[6] It shares 24% of its genome with members of the Archaea; the highest percentage overlap of any bacteria.[9] This similarity suggests horizontal gene transfer between Archaea and ancestors of T. maritima and could help to explain why T. maritima is capable of surviving in such extreme temperatures and conditions. The genome of T. maritima has been sequenced multiple times. Genome resequencing of T. maritima MSB8 genomovar DSM3109 [10][8] determined that the earlier sequenced genome was an evolved laboratory variant of T. maritima with an approximately 8-kb deletion. Moreover, a variety of duplicated genes and direct repeats in its genome suggest their role in intra-molecular homologous recombination leading to genes deletion. A strain with a 10-kb gene deletion has been developed using the experimental microbial evolution in T. maritima.[11]

Genetic system of T. maritima

T. maritima has a great potential in hydrogen synthesis because it can ferment a wide variety of sugars and has been reported to produce the highest amount of H2 (4 mol H2/ mol glucose).[3] Due to lack of a genetic system for the past 30 years majority of the studies have been either focused on heterologous gene expression in E. coli or predicting models since a gene knockout mutant of T. maritima remained unavailable.[12] Developing a genetic system for T. maritima has been a challenging task primarily because of a lack of a suitable heat-stable selectable marker. Recently, the most reliable genetic system based on pyrimidine biosynthesis has been established in T. maritima.[13] This newly developed genetic system relies upon a pyrE− mutant that was isolated after cultivating T. maritima on a pyrimidine biosynthesis inhibiting drug called 5-fluoroorotic acid (5-FOA). The pyrE− mutant is an auxotrophic mutant for uracil. The pyrE from a distantly related genus of T. maritima rescued the uracil auxotrophy of the pyrE− mutant of T. maritima and has been proven to be a suitable marker.

For the first time, the use of this marker allowed the development of an arabinose (araA) mutant of T. maritima. This mutant explored the role of the pentose phosphate pathway of T. maritima in hydrogen synthesis.[13] The genome of T. maritima possesses direct repeats that have developed into paralogs.[11] Due to lack of a genetic system the true function of these paralogs has remained unknown. Recently developed genetic system in T. maritima has been very useful to determine the function of the ATPase protein (MalK) of the maltose transporter that is present in a multi-copy (three copies) fashion. The gene disruptions of all three putative ATPase encoding subunit (malK) and phenotype have concluded that only one of the three copies serves as an ATPase function of the maltose transporter.[14] It is interesting to know that T. maritima has several paralogs of many genes and the true function of these genes is now dependent upon the use of the recently developed system. The newly developed genetic system in T. maritima has a great potential to make T. maritima as a host for hyperthermophilic bacterial gene expression studies. Protein expression in this model organism is promising to synthesize fully functional protein without any treatment.

Evolution

T. maritima contains homologues of several competence genes, suggesting that it has an inherent system of internalizing exogenous genetic material, possibly facilitating genetic exchange between this bacterium and free DNA.[6] Based on phylogenetic analysis of the small sub-unit of its ribosomal RNA, it has been recognized as having one of the deepest lineages of Bacteria. Furthermore, its lipids have a unique structure that differs from all other bacteria.[3]

References
  1. Merrill, Alfred H.; Lingrell, Susanne; Wang, Elaine; Nikolova-Karakashian, Mariana; Vales, Teresa R.; Vance, Dennis E. (1995-06-09). "Sphingolipid Biosynthesisde Novoby Rat Hepatocytes in Culture". Journal of Biological Chemistry. 270 (23): 13834–13841. doi:10.1074/jbc.270.23.13834. ISSN 0021-9258. PMID 7775441.
  2. "Hyperthermophilic organism that shows extensive horizontal gene transfer from archaea". BioProject. National Center for Biotechnology Information. 2003. Retrieved January 14, 2012.
  3. Robert Huber; Thomas A. Langworthy; Helmut König; Michael Thomm; Carl R. Woese; Uwe B. Sleytr & Karl O. Stetter (1986). "Thermotoga maritima sp. nov. represents a new genus of unique extremely thermophilic eubacteria growing up to 90°C". Archives of Microbiology. 144 (4): 324–333. doi:10.1007/BF00409880. S2CID 12709437.
  4. Jenny M. Blamey & Michael W. W. Adams (1994). "Characterization of an ancestral type of pyruvate ferredoxin oxireductase from the hyerpthermophilic bacterium, Thermotoga maritima". Biochemistry. 33 (4): 1000–1007. doi:10.1021/bi00170a019. PMID 8305426.
  5. "Geothermal organisms". Montana State University. Retrieved January 14, 2012.
  6. Karen E. Nelson; Rebecca A. Clayton; Steven R. Gill; Michelle L. Gwinn; Robert J. Dodson; et al. (1999). "Evidence for lateral gene transfer between Archaea and Bacteria from genome sequence of Thermotoga maritima" (PDF). Nature. 399 (6734): 323–329. Bibcode:1999Natur.399..323N. doi:10.1038/20601. PMID 10360571. S2CID 4420157.
  7. "Unique Spectroscopic Properties of the HCluster in a Putative Sensory [FeFe] Hydrogenase". dx.doi.org. doi:10.1021/jacs.7b11287.s001. Retrieved 2020-10-09.
  8. Latif, H; Lerman, J. A.; Portnoy, V. A.; Tarasova, Y; Nagarajan, H; Schrimpe-Rutledge, A. C.; Smith, R. D.; Adkins, J. N.; Lee, D. H.; Qiu, Y; Zengler, K (2013). "The genome organization of Thermotoga maritima reflects its lifestyle". PLOS Genetics. 9 (4): e1003485. doi:10.1371/journal.pgen.1003485. PMC 3636130. PMID 23637642.
  9. Camilla L. Nesbo; Stéphane l'Haridon; Karl O. Stetter & W. Ford Doolittle (2001). "Phylogenetic analyses of two "archaeal" genes in Thermotoga maritima reveal multiple transfers between Archaea and Bacteria". Molecular Biology and Evolution. 18 (3): 362–375. doi:10.1093/oxfordjournals.molbev.a003812. PMID 11230537.
  10. Boucher, Nathalie; Noll, Kenneth M. (September 2011). "Ligands of Thermophilic ABC Transporters Encoded in a Newly Sequenced Genomic Region of Thermotoga maritima MSB8 Screened by Differential Scanning Fluorimetry". Applied and Environmental Microbiology. 77 (18): 6395–6399. doi:10.1128/AEM.05418-11. ISSN 0099-2240. PMC 3187129. PMID 21764944.
  11. Singh, Raghuveer; Gradnigo, Julien; White, Derrick; Lipzen, Anna; Martin, Joel; Schackwitz, Wendy; Moriyama, Etsuko; Blum, Paul (2015-05-28). "Complete Genome Sequence of an Evolved Thermotoga maritima Isolate". Genome Announcements. 3 (3): e00557–15. doi:10.1128/genomeA.00557-15. ISSN 2169-8287. PMC 4447916. PMID 26021931.
  12. Conners, Shannon B.; Montero, Clemente I.; Comfort, Donald A.; Shockley, Keith R.; Johnson, Matthew R.; Chhabra, Swapnil R.; Kelly, Robert M. (2005-11-01). "An Expression-Driven Approach to the Prediction of Carbohydrate Transport and Utilization Regulons in the Hyperthermophilic Bacterium Thermotoga maritima". Journal of Bacteriology. 187 (21): 7267–7282. doi:10.1128/jb.187.21.7267-7282.2005. ISSN 0021-9193. PMC 1272978. PMID 16237010.
  13. White, Derrick; Singh, Raghuveer; Rudrappa, Deepak; Mateo, Jackie; Kramer, Levi; Freese, Laura; Blum, Paul (2017-02-15). "Contribution of Pentose Catabolism to Molecular Hydrogen Formation by Targeted Disruption of Arabinose Isomerase (araA) in the Hyperthermophilic Bacterium Thermotoga maritima". Applied and Environmental Microbiology. 83 (4): e02631–16. doi:10.1128/aem.02631-16. ISSN 0099-2240. PMC 5288831. PMID 27940539.
  14. Singh, Raghuveer; White, Derrick; Blum, Paul (2017-09-15). "Identification of the ATPase Subunit of the Primary Maltose Transporter in the Hyperthermophilic Anaerobe Thermotoga maritima". Applied and Environmental Microbiology. 83 (18): e00930–17. doi:10.1128/aem.00930-17. ISSN 0099-2240. PMC 5583491. PMID 28687653.
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