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Thioploca was discovered in 1907 by R. Lauterborn and is a genus of sulphur-oxidizing bacteria, belonging to the order Thiotrichales, part of the Gammaproteobacteria. They inhabit as well marine as freshwater environments, with vast communities present off the Pacific coast of South America and other areas with a high organic matter sedimentation and bottom waters rich in nitrate and poor in oxygen. [1][2]A large vacuole occupies more than 80% of their cellular volume and is used as a storage for nitrate. This nitrate is used for the sulphur oxidation, an important characteristic of the genus.[1]Due to their unique size in diameters, ranging from 15-40 µm, they are considered part of the largest bacteria known.[2]Because they use both sulfur and nitrogen compounds they may provide an important link between the nitrogen and sulphur cycles. [3]
Taxonomy and Identification
The genus Thioploca was first described by German botanist R. Lauterborn in 1907, who discovered them in Lake Constance, Germany.[4] Since this discovery, according to the NCBI database, a total of four species of Thioploca have been validly published: two freshwater species (Thioploca ingrica and Thioploca schmidlei) and two marine species (Thioploca araucae and Thioploca chileae).[5]
The defining characteristic of Thioploca species is a filamentous morphology, aggregating into bundles enclosed within a polysaccharide sheath, with an either parallel or braided appearance.[6] [7] These bundles can reach several cm, making them easy to recognise.[8] Occasionally they are also found as free-living trichomes, making them morphologically similar to the genus Beggiatoa. As Thioploca species also show a close phylogenetic affiliation to this genus and similar metabolic strategies, they are often mistaken as a species of Beggiatoa.[9]
The four species are differentiated on the basis of their trichome diameters. The two marine species are unique in having diameters up to 43 µm (T. araucae 30-43 µm; T. chileae 12-20 µm), placing them amongst some of the largest prokaryotic structures. [7] [9] The freshwater species T. ingrica and T. schmidlei morphologically resemble the well characterised marine Thioploca species, but show a smaller trichome diameter. Although some morphological and phylogenetic differences have been found between marine and non-marine species, knowledge about freshwater and brackish Thioploca is still limited, as its ecology is poorly studied so far. [10] [11]
Cultivation
The pure cultivation of Thioploca has so far not been successful. Natural populations can be kept alive for several months near the in-situ temperature of 13°C in anoxic seawater with added nitrate, but their need for a delicate balance of sulphide, nitrate and oxygen concentrations make an enrichment very difficult. Biochemical and physiological studies with harvested Thioploca filaments need to be handled carefully in order to avoid enzymatic activities due to air exposure. [6]
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- ^ ISSN 0168-6496.
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- EurekAlert!.
- ^ Lauterborn, R. (1907). "A new genus of sulfur bacteria". Ber. Dtsch. Bot. Ges.: 25, 238^242.
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- ^ a b Teske, Andreas; Nelson, Douglas C. (2006), "The Genera Beggiatoa and Thioploca", The Prokaryotes, New York, NY: Springer New York, pp. 784–810, retrieved 2021-12-10
- ^ )
- ISSN 0168-6496.
- ^ ISSN 1751-7362.
- ^ Hogslund, S. (2010). "Distribution, ecology and molecular identification of Thioploca from Danish brackish water sediments". FEMS Microbial Ecology. 73: 110–120.
- ^ Nemoto, F. (2011). "Diversity of freshwater Thioploca species and their specific association with filamentous bacteria of the phylum Chloroflexi". FEMS Microbial Ecology. 62: 753–764.