Do Bacteria Help Crustaceans Survive Inhabitable Conditions?

Bacteria were the first organisms to colonize earth. It is believed that the first life-forms appeared underwater close to deep-sea hydrothermal vents because the surface of the early Earth was inhabitable. Even today some bacteria are still adapted to live in extremely harsh conditions, like in the vicinity of hydrothermal vents, or even in places that are permanently cold, with temperatures below freezing. We call these organisms extremophiles.

We know that nowadays the big majority of the organic biomass is being produced by a process called photosynthesis, done by a large variety of organisms from phytoplankton to vascular plants. But this is not the first autotrophic process to appear in the history of life.

As we have discussed previously the first life forms that appeared on Earth were bacteria that lived near the deep-sea hydrothermal vents. These bacteria instead of using the energy of photons from the sun, break the chemical bonds of substances that don’t contain carbon in order to get their energy. Some of the inorganic chemicals chemoautotrophic bacteria use are hydrogen sulfide, ammonia, or other compounds such as iron (Dobrinski, 2005).

For example, the sulfur-oxidizing bacteria Thiothrix breaks down hydrogen sulfide to produce water and sulfur. The energy that is stored in the chemical bonds of the hydrogen sulfide molecule is released during the reaction. The bacteria use this energy along with carbon dioxide to make organic matter such as sugars and other carbohydrates. Some such bacteria can also be found in a few cave ecosystems. One such ecosystem can be found in Movile Cave, Romania (Chen et al., 2009).

Symbiosis is a vital relationship between two organisms, in which each one of them obtains benefits from the relationship. Symbiosis had a critical role in the apparition and development of Eukaryotes and is still one of the major driving forces of evolution to this day (Bauermeister et al., 2012).
Ectosymbioses between invertebrates and sulfur-oxidizing bacteria are widespread in sulfidic marine environments and have evolved independently in several invertebrate phyla. A few invertebrates that live in sulfur-rich habitats close to deep-sea hydrothermal vents, cold seeps, and in organic-rich coastal sediments, have sulfur-oxidizing bacteria on their body surfaces (Goffredi, 2010). Even though these animals live together with a multitude of free-living bacteria, and so they could be susceptible to colonization by some other opportunistic surface-dwellers, some have developed long-term relationships with only a few sulfur-oxidizing bacteria. Bacteria from the Thiovulgaceae and Thiotrichaceae families seem to have evolved an enhanced ability to establish ectosymbioses. Some examples of such ectosymbioses have been described both in marine and sulfur-rich cave waters in some species of crustaceans, especially in amphipods (Bauermeister et al., 2012).

In Frasassi Cave in Italy, there have been identified 3 species of amphipods of the genus Niphargus (N. ictus, N. frasassianus and N. montanarius) have ectosymbionts of the Thiothrix genus present on their body (Fig.1) (Bauermeister et al., 2012). Thick mats of sulfur-oxidizing bacteria cover some of the cave’s water bodies, but the ones that colonized the body surface of the amphipods are distinct from the natant Thiothrix bacteria (Dattagupta et al., 2009). This means that the ectosymbiotic bacteria have evolved together with the amphipods. Such a type of symbiosis was also described in Movile cave between Niphargus species and Thiothrix bacteria.

These species of amphipods from Frasassi and Southern Dobrogea are not closely related, however, their association with species of Thiothrix are remarkably alike. The similar Niphargus–Thiothrix associations in aquifers located 1200 km apart imply that these associations may be widespread in the groundwater ecosystems of Europe (Flot et al., 2014).
It is thought that a large variety of crustaceans that live in similar ecosystems have formed such symbiotic relationships, that are still out there to be observed and described. Scientists are still working to uncover the mysteries behind this relationship. Why do they form? What is the advantage the bacteria obtain from this relationship? When in the ontogeny of the crustaceans do these associations form and whatever these crustaceans can live in a sulfur-rich environment without the help of the bacteria.

References

1. Bauermeister J., Ramette A., Dattagupta S. (2012) Repeatedly Evolved Host-Specific Ectosymbioses between Sulfur-Oxidizing Bacteria and Amphipods Living in a Cave Ecosystem. PLoS ONE 7(11): e50254. doi:10.1371/journal.pone.0050254
2. Chen, Y., Wu, L., Boden, R., Hillebrand-Voiculescu, A. M., Kumaresan, D., Moussard, H., Baciu, M., Lu, Y., Murrell, J. C. (2009). Life without light: Microbial diversity and evidence of sulfur- and ammonium-based chemolithotrophy in Movile Cave. ISME J., 3(9): 1093-1104.
3. Dattagupta S., Schaperdoth I., Montanari A., Mariani S., Kita N, et al. (2009) A novel symbiosis between chemoautotrophic bacteria and a freshwater cave amphipod. ISME J., 3: 935–943.
4. Dobrinski, K. P. (2005). “The Carbon-Concentrating Mechanism of the Hydrothermal Vent Chemolithoautotroph Thiomicrospira crunogena”. J. Bacteriol., 187 (16): 5761–5766.
5. Flot, J.-F.; Bauermeister, J.; Brad, T.; Hillebrand-Voiculescu, A.; Sarbu, S.M.; Dattagupta, S. (2014) Niphargus-Thiothrix Associations May Be Widespread in Sulphidic Groundwater Ecosystems: Evidence from Southeastern Romania. Mol. Ecol., 23, 1405–1417.
6. Goffredi S (2010) Indigenous ectosymbiotic bacteria associated with diverse hydrothermal vent invertebrates. Environ. Microbiol. Rep 2: 479–488.