Spirochaeta

Figure 1.A:Colorful microbial mats in Octopus Spring in Yellowstone National Park, B:Cross-section of microbial mat, C:Unrooted neighbor-joining tree of protein sequences for type 1 reaction centers from Cyanobacteria, Chlorobi, Heliobacteria, and PscA-like sequence in Cab. thermophilum, Reproduced with permission of Dr. D. A. Bryant [1]

Classification

Domain Bacteria;

Phylum Spirochetes;

Class Spirochetes;

Order Spirochaetales;

Family Spirochaetaceae

[Others may be used. Use NCBI link to find]

Species

NCBI: Taxonomy

Genus species

1. Spirochaeta africana
2. Spirochaeta alkalica
3. Spirochaeta americana
4. Spirochaeta asiatica
5. Spirochaeta aurantia
6. Spirochaeta bajacaliforniensis
7. Spirochaeta caldaria
8. Spirochaeta coccoides
9. Spirochaeta halophila
10. Spirochaeta isovalerica
11. Spirochaeta litoralis
12. Spirochaeta smaragdinae
13. Spirochaeta stenostrepta
14. Spirochaeta taiwanensis
15. Spirochaeta thermophila
16. Spirochaeta xylanolyticus
17. Spirochaeta zuelzerae

Description and Significance

The genus Spirochaeta represents a group of free-living, saccharolytic non-pathogenic, obligate or facultative anaerobic helical shaped bacteria. Isolated strains have been obtained from a variety of freshwaters and marine waters (Table 1). In addition, culture-independent studies revealed the presence of Spirochaeta species in other environments such as anaerobic bioreactors (Ariesyada et al., 2007), and the digestive tract of termites (Noda et al., 2003). A number of members of the genus Spirochaeta inhabit extreme environments with respect to temperature, salinity, and pressure (e.g., Hoover et al., 2003; Aksenova et al., 1992). These microorganisms may hence harbor enzymes with potential biotechnological applications.

Genome Structure

At present, a fully closed genome sequence of a member of Spirochaeta genus is not available. However, the genome size of three species of Spirochaeta are known.

      1) Spirochaeta asiatica: 2.1 Mb
      2) Spirochaeta alkalica: 2.7 Mb
      3) Spirochaeta africana: 2.5 Mb (intro with description)

Using HPLC(High Performance Liquid Chromatography), it was found that the DNA of Spirochaeta species have G+C contents ranging from 51-65 mol%. (no genome)

Figure 4.A: Photomicrograph of a 5 day old culture of Cab. thermophilum and Anoxybacillus sp. grown in the light, B: Fluorescence micrograph of the same culture. Reproduced with permission of Dr. D. A. Bryant [1]

Figure 4.A: Photomicrograph of a 5 day old culture of Cab. thermophilum and Anoxybacillus sp. grown in the light, B: Fluorescence micrograph of the same culture. Reproduced with permission of Dr. D. A. Bryant [1]

Cell Structure, Metabolism and Life Cycle

The morphology and cellular structure of Spirochaeta spp. (and most other Spirochetes) is unique among prokaryotes. The cells are helical in shape and consist of an outer membrane, axial filaments (ultrastructurally similar to bacterial flagella), and a protoplasmic cylinder. The outer membrane or the outer sheath surrounds all of the structures including the axial filaments and the protoplasmic cylinder. The protoplasmic cylinder is the cell body of the organism. It is coiled and is composed of the cytoplasm, the nuclear region and the peptidoglycan-cytoplasmic membrane complex. The axial filaments are usually called the periplasmic flagella but are also known as periplasmic fibrils, axial fibrils and endoflagella. The cell normally has two periplasmic flagella with each one running most of the length of the cell so there is region where the two flagella overlap and gives an arrangement of “1-2-1” meaning that looking at the cell from right to left, there is one flagella at first then two flagella at the region where they overlap and then one again when only the second flagella is present. Points where these flagella attach can be found at the ends of the cell. Figure 13A shows an illustration of a Spirocheata cell showing the outer sheath, the protoplasmic cylinder and the periplasmic flagella. The periplasmic fibrils are found in between the outer membrane and the protoplasmic cylinder (Figure 13B). As mentioned earlier, all species of Spirochaeta have two periplasmic flagella with only one exception, Spirochaeta plicatilis. This species is a large member of Spirochaeta and has 18 to 20 periplasmic flagella inserted near each end of the protoplasmic cylinder. Also, the periplasmic flagella of the spirochete is permanently wound around the cell body and is endocellular. This gives these bacteria a very unique system for motility unlike other flagellated bacteria where their flagella are extracellular and are in direct contact with the environment.

The axial filaments reside under the outer membrane and are responsible for the unique mobility behavior of Spirochetes, a trait which has been linked to the pathogenicity of certain genera. Although the helical shape is typical for members of the Spirochetes phylum, a coccoid shaped Spirochaeta spp. was recently isolated from a termite gut by Droge et al. (2006).

The cell cycle of Caulobacter showing the two daughter cells, one with a stalk and one with a flagellum, that are different in function and structure. From Jacobs-Wagner

The Spirochaeta genus contains a group a saccharolytic and dissipotrophic bacteria, responsible for decomposition of (poly)carbohydrates in many aquatic environments. All species of the Spirochaeta genus ferment carbohydrates with formation of acetate, ethanol, CO2, and H2 as major end products. In addition, Spirochaeta isovalerica ferments a number of amino-acids in addition to carbohydrates. All isolated Spirochaeta species utilize the Embden-Meyerhof pathway for glucose catabolization with formation of pyruvate.

Ecology and Applications

Species of the Spirochaeta genus are common inhabitants of a variety of aquatic environments, such as the water, sediments and muds of ponds, marshes, lakes, rivers and oceans. In these environments, Spirochaeta are capable of competing with other microorganisms for available nutrients by exhibiting various types of mobility behaviors. The unique mobility of Spirochetes is due to the helical shape of the cells and the polar positioning of the axial filaments.

It has also been known that one of its species, Spirocheata caldaria, probably forms symbiotic relationships with the bacteria, Clostridium thermocellum. Spirochaeta caldaria is a thermophilic spirochete taken from a freshwater hot spring. A study conducted by Pohlschroeder et al. showed that cellulose degradation is enhanced in Clostridium thermocellum when the spirochete is present within its environment.

Also, experiements have shown that some species of Spirochaeta could possibly be used in the direct bioconversion of cellulose-containing wastes to fuel such as ethanol or hydrogen gas.

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Author

Page authored by Dieter Maurice Tourlousse and Godfrey Josef Torres, students of Prof. Jay Lennon at Michigan State University.