Thiomicrospira crunogena

A Microbial Biorealm page on the genus Thiomicrospira crunogena

Classification

Higher order taxa

Bacteria(Domain); Proteobacteria(Phylum); Gammaproteobacteria(Class); Thiotrichales(Order); Piscirickettsiaceae(Family)

Genus & Species

NCBI: Taxonomy

Thiomicrospira (Genus) crunogena (Species)

Description and significance

Thiomicrospira crunogena is a colorless sulfur-oxidizing bacterium isolated from deep-sea hydrothermal vents. It is a member of the genus Thiomicrospira, which are marine, spiral-shaped sulfur oxidizing bacteria. Much like photosynthetic bacteria and plants use the sun’s energy to fix carbon, T. crunogena uses the oxidation of reduced sulfur compounds (sulfide, thiosulfate, and elemental sulfur) as an energy source for carbon fixation and cellular maintenance. Its major source of carbon is the CO2 released from the hydrothermal vents. (1) Hydrothermal vents release hydrothermal fluid through fissures along the volcanically active mid-ocean ridge. These carbon dioxide and sulfide rich hot fluids periodically mix with cold, oxygenated bottom water, forcing T. crunogena to adapt to the dramatic fluctuations in the environmental conditions. One way T. crunogena copes with these oscillations is by using carbon concentrating mechanisms (see Cell Structure and Metabolism Section) that allow the cell’s growth to continue when carbon dioxide levels drop.(2)

Thiomicrospira crunogena was originally isolated from the hydrothermal vents of East Pacific Rise. (1) It is the first deep-sea autotrophic hydrothermal vent bacterium to have its genome completely sequenced and annotate.(3) With the first complete genome of a cosmopolitan autotrophic hydrothermal vent bacterium, researchers can further explore the genetic and physiological mechanisms that allow life to thrive in hostile environments at the bottom of the sea. And by comparing the T. crunogena’s genome to the genomes of autotrophic bacteria living in other extreme environments around the world, they can begin to piece together the evolutionary history of these extreme organisms.

Genome structure

The T. crunogena genome is confined to a single circular chromosome consisting of 2.43 megabase pairs, with a GC content of 43.1% and a high coding density which codes for 2196 proteins and 55 RNAs. The chromosome is densely packed with genes involved in electron transport (used to gain energy from sulfur compounds), energy and carbon metabolism, along with those required for nucleotide and amino acid synthesis and other cellular processes. The genome included a relative abundance of coding sequences encoding regulatory proteins: some proteins are used to control the expression of genes encoding carboxysomes, some are used to regular multiple dissolved inorganic nitrogen and phosphate transporters, as well as a phosphonate operon, which provide this species with a variety of options for acquiring these substrates from the environment. It is a perfect illustration of many of adaptations that T. crunogena have adapted to thrive at the hydrothermal vents around the globe. (4) All the components of the Sox system, a sulfur-oxidizing pathway, were found in the T. crunogena’s genome. Together, these Sox genes completely oxidize, or strip electrons, from a variety of reduced sulfur-related compounds (producing sulfate). The microbe also harbors an enzyme that stops short of complete oxidation to sulfate (producing elemental sulfur instead), which adds to the regulation and control of the system. T. crunogena has proportionally more regulatory and signaling molecules than a free-living planktonic species. This enhanced repertoire reflects the different demands of life in extreme, volatile conditions—which requires rapid, flexible cellular responses—compared with the relatively stable existence of plankton floating on the open ocean.(4) A putative prophage genome was found in the T. crunogena chromosome while no plasmid was found. The putative prophage is 38,090 base pairs long and contains 54 coding sequences. The prophage genome begins with a tyrosine integrase and contains a cI-like repressor gene. (4) The genome sequence provides a reference point for uncultivated chemoautotrophic sulfur-oxidizing bacteria.

Cell structure and metabolism

T. crunogena is a gram negative, spiral shaped cell with 2 membranes. It utilizes flagella for movement and Type IV pilus for attachment.(5) Although they are found from deep-sea thermal vents, the optimum temperature for its growth is at 28-32°C, which makes it a mesophile. (10)

To provide the energy necessary for carbon fixation and cell maintenance, T. crunogena is capable of using hydrogen sulfide, thiosulfate, elemental sulfur, and sulfide minerals as electron donors; the only electron acceptor it can use is oxygen.The system that oxidizes sulfur is called Sox system, this system involves a periplasmic multienzyme complex that is capable of oxidizing various reduced sulfur compounds completely to sulfate. With the oxidation of sulfide to elemental sulfur, there are usually depositions of sulfur outside the cells. (4)

The chemical and physical characteristics of the bacteria’s environment are dictated largely by the interaction of hydrothermal fluid and bottom seawater. When warm CO2 rich hydrothermal fluid is emitted from crust, it mixes with cold, oxygen rich bottom seawater. As a consequence, at areas where dilute hydrothermal fluid and seawater mix, T. crunogena‘s habitat is erratic, oscillating from seconds to hours between dominance by hydrothermal fluid and bottom water. Given its volatile environment, T. crunogena has a carbon concentrating mechanism that enables it to grow in the presence of low concentrations of CO2 by generating an elevated concentration of intracellular dissolved inorganic carbon. This species is capable of rapid growth in the presence of low concentrations of dissolved inorganic carbon, due to an increase in cellular affinity for both HCO3− and CO2 under low CO2 conditions.(6) The ability to grow under low CO2 conditions is an advantage when the habitat is dominated by relatively low CO2 seawater.(7)

Ecology

T. crunogena can be found world wide. Originally isolated from the East Pacific Rise, it was subsequently cultivated or detected with molecular methods from deep-sea vents in both the Pacific and Atlantic. Also, closely related species have been found at shallow-water hydrothermal vents. (4) Because of its sulfur oxidizing ability, T. crunogena can play a prominent role in biogeochemical sulfur cycling. It is important to marine habitats, because a huge population of these bacteria can reduce the O2 concentration in the seawater by releasing the oxidized sulfur compound. (8) Also, the release of the sulfur compound can affect the pH of the environment. Like many sulfur-oxidizing chemoautotrophs, T. crunogena acidifies its environment as it grows, due to the accumulation of sulfuric acid produced as a result of sulfur oxidation.(9) No symbiotic relationship was found between T. crunogena and any other organisms.

Pathology

There is no known disease that is caused by this organism. It has not been found to be pathogenic.

Current Research

The physiological studies of carbon concentrating mechanism in T. crunogena are being conducted by the researchers. Researchers are trying to find out whether other bacteria can adapt the carbon concentrating mechanism and live at low inorganic carbon environment. By using chemostats, the researchers can determine the response of growth rate to the concentration of inorganic carbon present in the growth medium. No conclusion has been drawn. (9)

Field studies have been done at Lake Fryxell to examine the affect of these sulfur oxidizing bacteria on the environment. These bacteria have already made a part of the lake anoxic, and researchers found that the proliferation of these bacteria is mainly caused by the high sulfide content in the lake water. (8)

Experiments that include radio labeled inorganic carbon as the carbon source for T. crunogena are being conducted. From these experiments, researcher attempts to find the properties of the bicarbonate transporters, and how does it drive the intracellular inorganic carbon concentrations. Hopefully these experiments can shed light on the exact physiological pathway for the inorganic carbons in these bacteria. No conclusion has been drawn. (9)

References

1. Jannasch H, Wirsen C, Nelson D, Robertson L. Thiomicrospira crunogena sp. nov., a colorless, sulfur-oxidizing bacterium from a deep-sea hydrothermal vent. Int J Syst Bacteriol. 1985;35:422–424.

2. Scott KM, Bright M, Fisher CR. The burden of independence: Inorganic carbon utilization strategies of the sulphur chemoautotrophic hydrothermal vent isolate Thiomicrospira crunogena and the symbionts of hydrothermal vent and cold seep vestimentiferans. Cah Biol Mar. 1998;39:379–381.

3. Dufresne A, Salanoubat M, Partensky F, Artiguenave F, Axmann I, et al. Genome sequence of the cyanobacterium Prochlorococcus marinus SS120, a nearly minimal oxyphototrophic genome. Proc Natl Acad Sci U S A. 2003;100:10020–10025. http://www.ncbi.nlm.nih.gov/sites/entrez?db=PubMed&cmd=Retrieve&list_uids=12917486

4. Scott KM, Sievert SM, Abril FN, Ball LA, Barrett CJ, Blake RA, Boller AJ, Chain PS, Clark JA, Davis CR, et al. PLoS Biol. 2006;4:e383. http://www.ncbi.nlm.nih.gov/sites/entrez?db=PubMed&cmd=Retrieve&list_uids=17105352

5. HAMAP: Thiomicrospira crunogena (strain XCL-2) complete proteome ExPASy Home page http://expasy.org/sprot/hamap/THICR.html

6. Dobrinski KP, Longo DL, Scott KM. A hydrothermal vent chemolithoautotroph with a carbon concentrating mechanism. J Bacteriol. 2005;187:5761–5766. http://www.ncbi.nlm.nih.gov/sites/entrez?db=PubMed&cmd=Retrieve&list_uids=16077123

7. Wirsen CO, Brinkhoff T, Kuever J, Muyzer G, Molyneaux S, et al. Comparison of a new Thiomicrospira strain from the Mid-Atlantic Ridge with known hydrothermal vent isolates. Appl Environ Microbiol. 1998;64:4057–4059.

8. Sattley, W. M., and M. T. Madigan. 2006. Isolation, characterization, and ecology of cold-active, chemolithotrophic, sulfur-oxidizing bacteria from perennially ice-covered Lake Fryxell, Antarctica. Appl. Environ. Microbiol. 72:5562-5568. http://aem.asm.org/cgi/content/full/72/8/5562

9. KATHLEEN M. SCOTT, Ph.D. USF Research Webpage http://uweb.cas.usf.edu/~kscott/details.htm

10. NCBI Genome Project, Thiomicrospira crunogena XCL-2 project at DOE Joint Genome Institute http://www.ncbi.nlm.nih.gov/sites/entrez?db=genomeprj&cmd=Retrieve&dopt=Overview&list_uids=13018

Edited by Xiang Zhang of Rachel Larsen