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== Genetic information ==
== Genetic information ==
Based on the 16S rRNA sequences''''',''''' ''Thioploca'' and ''[[Beggiatoa]]'' form a monophyletic, high diversified cluster belonging to [[Gammaproteobacteria]]''.'' However, the distinction between ''Thioploca'' and ''Beggiatoa'' does not follow phylogenetic lines but follows the formation of the sheath around the filament bundle, a morphological characteristic. The 16S rRNA data supports the fact that ''T. araucae'' and ''T. chileae'' are two different species. Moreover, ''Thioploca'' species show some phenotypic similarities with some [[cyanobacteria]] (for example ''Microcoleus),'' because both have the formation of sheaths around bundles of filaments. Nonetheless, the phylogenetic data shows that there isn't any kind of relationship between sulphide-oxidizing bacteria and cyanobacteria, and are therefore defined as separate monophyletic bacterial groups. <ref>{{Cite journal|last=Høgslund|first=Signe|last2=Revsbech|first2=Niels Peter|last3=Kuenen|first3=J. Gijs|last4=Jørgensen|first4=Bo Barker|last5=Gallardo|first5=Victor Ariel|last6=Vossenberg|first6=Jack van de|last7=Nielsen|first7=Jeppe Lund|last8=Holmkvist|first8=Lars|last9=Arning|first9=Esther T.|last10=Nielsen|first10=Lars Peter|date=2009-06|title=Physiology and behaviour of marine Thioploca|url=https://www.nature.com/articles/ismej200917|journal=The ISME Journal|language=en|volume=3|issue=6|pages=647–657|doi=10.1038/ismej.2009.17|issn=1751-7370}}</ref><ref>{{Cite journal|last=Larkin|first=John M.|last2=Strohl|first2=William R.|date=1983-10|title=BEGGIATOA , THIOTHRIX , AND THIOPLOCA|url=https://www.annualreviews.org/doi/10.1146/annurev.mi.37.100183.002013|journal=Annual Review of Microbiology|language=en|volume=37|issue=1|pages=341–367|doi=10.1146/annurev.mi.37.100183.002013|issn=0066-4227}}</ref><ref>{{Cite web|title=Download Limit Exceeded|url=https://citeseerx.ist.psu.edu/messages/downloadsexceeded.html|access-date=2021-12-24|website=citeseerx.ist.psu.edu}}</ref>
Based on the 16S rRNA sequences''''',''''' ''Thioploca'' and ''[[Beggiatoa]]'' form a monophyletic, high diversified cluster belonging to [[Gammaproteobacteria]]''.'' However, the distinction between ''Thioploca'' and ''Beggiatoa'' does not follow phylogenetic lines but follows the formation of the sheath around the filament bundle, a morphological characteristic. The 16S rRNA data supports the fact that ''T. araucae'' and ''T. chileae'' are two different species. Moreover, ''Thioploca'' species show some phenotypic similarities with some [[cyanobacteria]] (for example ''Microcoleus),'' because both have the formation of sheaths around bundles of filaments. Nonetheless, the phylogenetic data shows that there isn't any kind of relationship between sulphide-oxidizing bacteria and cyanobacteria, and are therefore defined as separate monophyletic bacterial groups. <ref>{{Cite journal|last=Høgslund|first=Signe|last2=Revsbech|first2=Niels Peter|last3=Kuenen|first3=J. Gijs|last4=Jørgensen|first4=Bo Barker|last5=Gallardo|first5=Victor Ariel|last6=Vossenberg|first6=Jack van de|last7=Nielsen|first7=Jeppe Lund|last8=Holmkvist|first8=Lars|last9=Arning|first9=Esther T.|last10=Nielsen|first10=Lars Peter|date=2009-06|title=Physiology and behaviour of marine Thioploca|url=https://www.nature.com/articles/ismej200917|journal=The ISME Journal|language=en|volume=3|issue=6|pages=647–657|doi=10.1038/ismej.2009.17|issn=1751-7370}}</ref><ref>{{Cite journal|last=Larkin|first=John M.|last2=Strohl|first2=William R.|date=1983-10|title=BEGGIATOA , THIOTHRIX , AND THIOPLOCA|url=https://www.annualreviews.org/doi/10.1146/annurev.mi.37.100183.002013|journal=Annual Review of Microbiology|language=en|volume=37|issue=1|pages=341–367|doi=10.1146/annurev.mi.37.100183.002013|issn=0066-4227}}</ref><ref>{{Cite web|title=Download Limit Exceeded|url=https://citeseerx.ist.psu.edu/messages/downloadsexceeded.html|access-date=2021-12-24|website=citeseerx.ist.psu.edu}}</ref>

== <big>Habitat</big> ==
The filamentous sulfur oxidizers ''Thioploca'' grows at oxic/anoxic interactions on freshwater, brackish and marine sediments where sulfide of biological and geothermal origin combines with oxygen or nitrate in the overlying water column.

Extensive rugs of ''Thioploca'' can be found on the Chilean and Peruvian continental shelf, where it grows on sediments that form the basis of deoxygenated water masses of the Peru-Chile countercurrent <ref>{{Cite journal|last=Huber|first=Anton|last2=Barriga|first2=Pablo|last3=Trecaman|first3=Ramiro|date=1998|title=Efecto de la densidad de plantaciones de Eucalyptus nitens sobre el balance hídrico en la zona de Collipulli, IX Región (Chile)|url=http://dx.doi.org/10.4206/bosque.1998.v19n1-07|journal=Bosque|volume=19|issue=1|pages=61–69|doi=10.4206/bosque.1998.v19n1-07|issn=0304-8799}}</ref>''. Thioploca'' has been found in coastal regions with analogous upwelling regimes, where high organic productivity creates significant oxygen depletion at the bottom waters that covers organic-rich sediments with high sulfate reduction rates. Examples include the coast of Oman <ref>{{Cite journal|last=Schmaljohann|first=R|last2=Drews|first2=M|last3=Walter|first3=S|last4=Linke|first4=P|last5=von Rad|first5=U|last6=Imhoff|first6=JF|date=2001|title=Oxygen-minimum zone sediments in the northeastern Arabian Sea off Pakistan: a habitat for the bacterium Thioploca|url=http://dx.doi.org/10.3354/meps211027|journal=Marine Ecology Progress Series|volume=211|pages=27–42|doi=10.3354/meps211027|issn=0171-8630}}</ref>, and the Benguela current ecosystem off Namibia <ref>{{Cite journal|last=Gallardo|first=V.A.|last2=Klingelhoeffer|first2=E.|last3=Arntz|first3=W.|last4=Graco|first4=M.|date=1998-08|title=First Report of the BacteriumThioplocain the Benguela Ecosystem off Namibia|url=http://dx.doi.org/10.1017/s0025315400044945|journal=Journal of the Marine Biological Association of the United Kingdom|volume=78|issue=3|pages=1007–1010|doi=10.1017/s0025315400044945|issn=0025-3154}}</ref>. Other reported marine habitats include the monsoon-driven upwelling area of the northwestern Arabian Sea <ref>{{Cite journal|last=Lamont|first=Peter A|last2=Gage|first2=John D|date=2000-01|title=Morphological responses of macrobenthic polychaetes to low oxygen on the Oman continental slope, NW Arabian Sea|url=http://dx.doi.org/10.1016/s0967-0645(99)00102-2|journal=Deep Sea Research Part II: Topical Studies in Oceanography|volume=47|issue=1-2|pages=9–24|doi=10.1016/s0967-0645(99)00102-2|issn=0967-0645}}</ref> and hydrothermal vent sites in the eastern Mediterranean Sea <ref>{{Cite journal|date=1996-11|title=Directional coronary atherectomy survey summary|url=http://dx.doi.org/10.1016/s1063-4282(96)90013-1|journal=Interventional Cardiology Newsletter|volume=4|issue=6|pages=45–47|doi=10.1016/s1063-4282(96)90013-1|issn=1063-4282}}</ref>.

Classical localities of the freshwater species are lakes in central and northern Europe<ref>{{Cite journal|last=Westheide|first=Wilfried|date=1965-07|title=Parapodrilus psammophilus nov. gen. nov. spec., eine neue Polychaeten-Gattung aus dem Mesopsammal der Nordsee|url=http://dx.doi.org/10.1007/bf01612099|journal=Helgoländer Wissenschaftliche Meeresuntersuchungen|volume=12|issue=1-2|pages=207–213|doi=10.1007/bf01612099|issn=0017-9957}}</ref> <ref>{{Cite journal|last=MAIER|first=S.|date=1984-07-01|title=Description of Thioploca ingrica sp. nov., nom. rev.|url=http://dx.doi.org/10.1099/00207713-34-3-344|journal=International Journal of Systematic Bacteriology|volume=34|issue=3|pages=344–345|doi=10.1099/00207713-34-3-344|issn=0020-7713}}</ref> <ref>{{Cite journal|last=Koppe-Kiel|first=Fr.|date=1922-01|title=Die Schlammflora ostholsteinischer Seen und des Bodensees|url=http://dx.doi.org/10.1080/03680770.1923.11896452|journal=SIL Proceedings, 1922-2010|volume=1|issue=1|pages=94–97|doi=10.1080/03680770.1923.11896452|issn=0368-0770}}</ref> <ref>{{Cite journal|date=1922-04|title=Ein neues Diaphanoskop|url=http://dx.doi.org/10.1007/bf01565756|journal=Die Naturwissenschaften|volume=10|issue=14|pages=336–336|doi=10.1007/bf01565756|issn=0028-1042}}</ref>, but they are also present in large lakes in North America, central Russia, and Japan <ref>{{Cite journal|last=Maier|first=S.|last2=Preissner|first2=W. C.|date=1979-06|title=Occurrence ofThioploca in Lake Constance and Lower Saxony, Germany|url=http://dx.doi.org/10.1007/bf02010502|journal=Microbial Ecology|volume=5|issue=2|pages=117–119|doi=10.1007/bf02010502|issn=0095-3628}}</ref> <ref>{{Cite journal|last=Dagurova|first=O. P.|last2=Namsaraev|first2=B. B.|last3=Kozyreva|first3=L. P.|last4=Zemskaya|first4=T. I.|last5=Dulov|first5=L. E.|date=2004-03|title=Bacterial Processes of the Methane Cycle in Bottom Sediments of Lake Baikal|url=http://dx.doi.org/10.1023/b:mici.0000023990.71983.c1|journal=Microbiology|volume=73|issue=2|pages=202–210|doi=10.1023/b:mici.0000023990.71983.c1|issn=0026-2617}}</ref> <ref>{{Cite journal|last=Nishino|first=Machiko|last2=Fukui|first2=Manabu|last3=Nakajima|first3=Takuo|date=1998-03|title=Dense mats of thioploca, gliding filamentous sulfur-oxidizing bacteria in lake Biwa, central Japan|url=http://dx.doi.org/10.1016/s0043-1354(97)00227-3|journal=Water Research|volume=32|issue=3|pages=953–957|doi=10.1016/s0043-1354(97)00227-3|issn=0043-1354}}</ref>.

== Ecological niche ==
By transporting nitrate intracellularly deep down into the anoxic seafloor, Thioploca appears to effectively eliminate the competition from other sulfide oxidizing bacteria, which are unable to store an electron acceptor for extended periods but need simultaneous access to both electron acceptor and donor in their immediate microenvironment. A similar storage of oxygen in the vacuoles would not be possible since the lipid membranes enclosing cells and vacuoles are permeable to gases. The thioplocas thus move up and down, recharging with nitrate at the surface and oxidizing sulfide at depth, therefore  storing elemental sulfur globules as an energy reserve <ref>{{Cite journal|last=Jørgensen|first=Bo B.|last2=Revsbech|first2=Niels P.|date=1983-04|title=Colorless Sulfur Bacteria,
Beggiatoa
spp. and
Thiovulum
spp., in O
2
and H
2
S Microgradients|url=http://dx.doi.org/10.1128/aem.45.4.1261-1270.1983|journal=Applied and Environmental Microbiology|volume=45|issue=4|pages=1261–1270|doi=10.1128/aem.45.4.1261-1270.1983|issn=0099-2240}}</ref> <ref>{{Cite journal|last=Nelson|first=Douglas C.|last2=Jørgensen|first2=Bo Barker|last3=Revsbech|first3=Niels Peter|date=1986-08|title=Growth Pattern and Yield of a Chemoautotrophic
Beggiatoa
sp. in Oxygen-Sulfide Microgradients|url=http://dx.doi.org/10.1128/aem.52.2.225-233.1986|journal=Applied and Environmental Microbiology|volume=52|issue=2|pages=225–233|doi=10.1128/aem.52.2.225-233.1986|issn=0099-2240}}</ref>.

== Thioploca and Beggiatoa ==
Although the thioplocas typically live in sheaths in bundles ranging from a few up to a hundred filaments per sheath, many were found at the sediment surface apparently without a sheath. At the Bay of Concepcion on the Chilean coast, there was a transition between an apparently pure Beggiatoa community inside the bay to a mixed community of both genera at the entrance of the bay to pure Thioploca outside. In the mixed community it was not possible to discriminate beggiatoas from thioplocas by simple microscopy but only by analyzing statistically their diameter distributions. The tapered ends of filaments, characteristic of Thioploca but absent in Beggiatoa, was not a consistent character of the thioplocas <ref>{{Cite journal|last=Schulz|first=H N|last2=Jorgensen|first2=B B|last3=Fossing|first3=H A|last4=Ramsing|first4=N B|date=1996-06|title=Community Structure of Filamentous, Sheath-Building Sulfur Bacteria, Thioploca spp., off the Coast of Chile|url=http://dx.doi.org/10.1128/aem.62.6.1855-1862.1996|journal=Applied and Environmental Microbiology|volume=62|issue=6|pages=1855–1862|doi=10.1128/aem.62.6.1855-1862.1996|issn=0099-2240}}</ref>.

Future changes in classification of Thioploca and Beggiatoa are likely. The range of strains over which the genus designation Beggiatoa is used is overly broad. More importantly, the differentiation between Thioploca and Beggiatoa is currently based on the formation of a common sheath surrounding filament bundles, a characteristic that might vary in response to environmental conditions. In the absence of pure cultures, it may be impossible to prove or disprove whether any natural population of vacuolated Beggiatoa will form sheath bundles in some specific environment. The clade comprised of three Thioploca strains, two Beggiatoa strains, and a Thiomargarita strain is united by the possession of a large central vacuole. This feature currently appears to be the best morphological candidate to replace sheath formation as a marker in a revised taxonomy of the group Beggiatoa–Thioploca. This marker, in addition to being consistent with 16S rRNA phylogeny, appears to be universally connected to intracellular nitrate accumulation, presumably in the vacuole, for nitrate respiration enabling sustained anaerobic metabolism. A future revision of the genus Thioploca, based on the vacuolated, nitrate-respiring phenotype and corresponding 16S rRNA clade, might include these gliding filaments regardless of whether they occur in sheathed bundles <ref>{{Cite book|url=https://onlinelibrary.wiley.com/doi/book/10.1002/9781118960608|title=Bergey's Manual of Systematics of Archaea and Bacteria|date=2015-04-17|publisher=Wiley|isbn=978-1-118-96060-8|editor-last=Whitman|editor-first=William B|edition=1|language=en|doi=10.1002/9781118960608.gbm01227|editor-last2=Rainey|editor-first2=Fred|editor-last3=Kämpfer|editor-first3=Peter|editor-last4=Trujillo|editor-first4=Martha|editor-last5=Chun|editor-first5=Jonsik|editor-last6=DeVos|editor-first6=Paul|editor-last7=Hedlund|editor-first7=Brian|editor-last8=Dedysh|editor-first8=Svetlana}}</ref>.


==References==
==References==

Revision as of 16:18, 29 December 2021

Thioploca
Scientific classification
Kingdom:
Bacteria
Phylum:
Proteobacteria
Class:
Gammaproteobacteria
Order:
Thiotrichales
Family:
Thiotrichaceae[1]
Genus:
Thioploca

Thioploca is a genus of filamentous sulfur bacteria which occurs along 3,000 kilometres (1,900 mi) of coast off the west of South America. A large vacuole occupies more than 80% of their cell volume and contains sulfide and nitrate which they use to make energy for their metabolism by oxidising sulfide with nitrate. The concentration of nitrate in the vacuole is extremely high (500 mM) even though the sediments in which they live are relatively very low in nitrogen (25 μM).[3] Because they use both sulfur and nitrogen compounds they may provide an important link between the nitrogen and sulfur cycles. They secrete a sheath of mucus which they use as a tunnel to travel between the sulfide containing sediment and the nitrate containing sea water.[4]

Metabolism

This particular genus shows interesting and not completely clarified metabolic pathways. This not well-known situation is due to the absence of no pure culture, but they seem to be mixotrophic sulphide oxidizers. Data in our hands are mainly recovered by several experiments conducted on entire communities or bundles of filaments.[5] The hypothesis suggested by research of the possible nature of methylotrophs organisms was rejected, mainly because the areas in which they were found are not very rich in methane.[6] Therefore, the small amount of methane concentration allows rejecting the possibilities of use of it for metabolic activity of a large population of these microorganisms.[7] More specific research has shown that, through the use of 14C-labeled, they do not incorporate this specific compound or methanol. On the other hand, they showed incorporation capacity CO2 and different substrates (acetate, amino acids, bicarbonate, glucose, glycine, etc). For this reason, these microorganisms are considered a very good example of mixotrophic bacteria.[8] [9]Their basic strategy is based on the presence of trichomes, aggregates in bundles surrounded by a sheath, even if sometimes they are found as free-living trichomes.  They are basically defined as sulphur bacteria, capable of oxidizing mainly H2S (Hydrogen sulphide, etc.) and accumulating NO3 (Nitrate) in a specific vacuole in their cells.[5] [9]In the vacuole the concentrations of nitrate can increase up to 0.5 M. [10]They have also shown the capacity to accumulate S0 (elemental sulphur) in the cells under the forms of drops, as a result of oxidation of hydrogen sulphide. These bacteria have developed this system (with morphological, physiological, and metabolic adaptation) to maintain a metabolism based on a different source of electron donor and acceptor, which are situated in a different zone in the water column and characterized by a different gradient. [9]

Oxygen uptake and resistance

These genera show a behavior typical of microaerophilic microorganisms. Data based on behavior and oxygen uptake experiment has confirmed their nature. They show an uptake rate of oxygen of 1760 µmol dm-3 h-1.[9] Even if they show an uptake rate similar to Thiomargarita spp., they do not have the same capacities to resist for a longer time in presence of oxygen.[11] For this reason, they populate OMZs (Oxygen Minimum Zone). [9]

Sulphur metabolism

Thioploca spp. has shown two types of response to sulphide based on its concentrations of it. They have a positive response to low sulphide (<100 µM) concentrations and negative to high concentrations.[6] [5]They show a maximum uptake rate at 200 µM.[9] This coupled with taxis towards nitrate, regulates the behavior of this genus. Also involved in it is the gradient of O2 affecting it in a minor way. For this reason, these microorganisms are defined as microaerophilic. Hypothetically they could be in competition with other sulphide oxidizing bacteria, but with the ability to accumulate nitrate they create a perfect strategy to access both electron donor and acceptor at the same moment. [12][6]

Based on some research, we know that oxidized iron is important in process of scavenging H2S (hydrogen sulphide), although the precise mechanism is unknown. [13]At the same time, the inhabited sheaths of Thioploca can be covered by filamentous sulphate-reducing bacteria. These sulphate-reducing bacteria, pertaining to the genus Desulfonema, could explain the high rate of recycling of H2S and its availability also in sulphide-pore environments. [6]

Furthermore, the elemental sulphur accumulated in the cells as drops is involved in sulphur metabolism. This reaction is also involved oxygen which oxidates the elemental sulphur:

2S0+3O2+ 2H2O → 4SO42-+ 4H+

Another reaction, involving nitrate, is part of the oxidation:

4S0+3NO3-+ 7H2O → 4SO42-+ 3NH4++2H+

These two reactions occur at similar rates. A difference is situated in the uptake rate of sulphide that is 5-6 times faster with respect to the oxidation rate of elemental sulphur stored in the drops. Based on this we know that sulphide uptake is not coupled with carbon fixation.[9]

Nitrogen metabolism

Thioploca genus has shown also the capacity to accumulate nitrate and use the Dissimilatory nitrate reduction to ammonium (DNRA) pathway.[14][9][5][6] To obtain nitrate they perform a vertical migration. Sheats of Thioploca spp. are considered a compatible niche for the growth of anammox bacteria, due to the ability of Thioploca spp. to perform Dissimilative nitrate reduction to ammonium. [9]They are able to perform nitrite reduction and show positive taxis towards nitrite. [14]The dissimilatory nitrate reduction is involved also in the oxidation of sulphide that leads to a higher accumulation of elemental sulphur. A higher presence and reduction of nitrate increase drastically the fixation of carbon dioxide (CO2). In any case, nitrate uptake can occur also in low environmental concentrations. [9]

Species

Thioploca contains four species:[15]

Morphology

Thioploca spp. can occur in both marine and freshwater environments, the difference between the two types being in the cell structure since the freshwater species are smaller.

These gram-negative bacteria can be described as flexible, univariate, colorless filaments made up of numerous cells and enclosed by a common gelatinous sheath[16]. Their cell shape can vary in relation to the organism size. In small-sized organisms the cells are usually disk-shaped, while in bigger ones it is more common to find cylindrical or barrel-shaped cells.

The cells are famous for the presence of sulfur inclusions within the cytoplasm and their arrangement in the structure of the organism is characterized by the presence of separation cross-walls among them. Cells of large marine Thioploca look hollow because of the presence of the vacuole full of stored nitrate.

In marine species, the diameter of the trichome (filament) reaches lengths from 15-40 μm to many cm; according to their diameter they can be divided into different species. Nevertheless, only two are considered valid today: the 12-20 μm wide Thioploca Chileae and the 30-43 μm wide Thioploca araucae.

Thioploca typically grow in bundles surrounded by a common sheath and the number of filaments for sheath varies from a rage of ten to hundred. This sheath changes its shape during the growth. In young organisms it is thin and tough, while in adults it becomes wide and loose.

Each filament consists of a single row of cylindrical or barrel-shaped cells separated by a septum[17]. In the latter ones, sulfur globules can be found and the cell wall has a complex, four-layered structure, of which the innermost layer and the cytoplasmic membrane go across the septum. Intracytoplasmic membranes and several cell inclusions form complex structures and their work is related to transport and storage.

Thioploca are organisms able to deposit sulfur granules, the most abundant being globules of when sulphide is present. They are located externally of the cytoplasmic membrane, in particular in invaginations of it, and are therefore considered extracytoplasmic. This location has two important consequences:

  • the diffusion of sulphide, that may not necessarily diffuse across the membrane to the cytoplasmic side. There it could undergo a disrupt metabolism, avoiding the toxic effects of sulphide ion
  • the oxidation of sulphide on the external surface of the cytoplasmic membrane, creating the proton gradient for the synthesis of ATP.

Genetic information

Based on the 16S rRNA sequences, Thioploca and Beggiatoa form a monophyletic, high diversified cluster belonging to Gammaproteobacteria. However, the distinction between Thioploca and Beggiatoa does not follow phylogenetic lines but follows the formation of the sheath around the filament bundle, a morphological characteristic. The 16S rRNA data supports the fact that T. araucae and T. chileae are two different species. Moreover, Thioploca species show some phenotypic similarities with some cyanobacteria (for example Microcoleus), because both have the formation of sheaths around bundles of filaments. Nonetheless, the phylogenetic data shows that there isn't any kind of relationship between sulphide-oxidizing bacteria and cyanobacteria, and are therefore defined as separate monophyletic bacterial groups. [18][19][20]

Habitat

The filamentous sulfur oxidizers Thioploca grows at oxic/anoxic interactions on freshwater, brackish and marine sediments where sulfide of biological and geothermal origin combines with oxygen or nitrate in the overlying water column.

Extensive rugs of Thioploca can be found on the Chilean and Peruvian continental shelf, where it grows on sediments that form the basis of deoxygenated water masses of the Peru-Chile countercurrent [21]. Thioploca has been found in coastal regions with analogous upwelling regimes, where high organic productivity creates significant oxygen depletion at the bottom waters that covers organic-rich sediments with high sulfate reduction rates. Examples include the coast of Oman [22], and the Benguela current ecosystem off Namibia [23]. Other reported marine habitats include the monsoon-driven upwelling area of the northwestern Arabian Sea [24] and hydrothermal vent sites in the eastern Mediterranean Sea [25].

Classical localities of the freshwater species are lakes in central and northern Europe[26] [27] [28] [29], but they are also present in large lakes in North America, central Russia, and Japan [30] [31] [32].

Ecological niche

By transporting nitrate intracellularly deep down into the anoxic seafloor, Thioploca appears to effectively eliminate the competition from other sulfide oxidizing bacteria, which are unable to store an electron acceptor for extended periods but need simultaneous access to both electron acceptor and donor in their immediate microenvironment. A similar storage of oxygen in the vacuoles would not be possible since the lipid membranes enclosing cells and vacuoles are permeable to gases. The thioplocas thus move up and down, recharging with nitrate at the surface and oxidizing sulfide at depth, therefore  storing elemental sulfur globules as an energy reserve [33] [34].

Thioploca and Beggiatoa

Although the thioplocas typically live in sheaths in bundles ranging from a few up to a hundred filaments per sheath, many were found at the sediment surface apparently without a sheath. At the Bay of Concepcion on the Chilean coast, there was a transition between an apparently pure Beggiatoa community inside the bay to a mixed community of both genera at the entrance of the bay to pure Thioploca outside. In the mixed community it was not possible to discriminate beggiatoas from thioplocas by simple microscopy but only by analyzing statistically their diameter distributions. The tapered ends of filaments, characteristic of Thioploca but absent in Beggiatoa, was not a consistent character of the thioplocas [35].

Future changes in classification of Thioploca and Beggiatoa are likely. The range of strains over which the genus designation Beggiatoa is used is overly broad. More importantly, the differentiation between Thioploca and Beggiatoa is currently based on the formation of a common sheath surrounding filament bundles, a characteristic that might vary in response to environmental conditions. In the absence of pure cultures, it may be impossible to prove or disprove whether any natural population of vacuolated Beggiatoa will form sheath bundles in some specific environment. The clade comprised of three Thioploca strains, two Beggiatoa strains, and a Thiomargarita strain is united by the possession of a large central vacuole. This feature currently appears to be the best morphological candidate to replace sheath formation as a marker in a revised taxonomy of the group Beggiatoa–Thioploca. This marker, in addition to being consistent with 16S rRNA phylogeny, appears to be universally connected to intracellular nitrate accumulation, presumably in the vacuole, for nitrate respiration enabling sustained anaerobic metabolism. A future revision of the genus Thioploca, based on the vacuolated, nitrate-respiring phenotype and corresponding 16S rRNA clade, might include these gliding filaments regardless of whether they occur in sheathed bundles [36].

References

  1. ^ eol
  2. ^ Jørgensen, B. B.; Gallardo, V. A. (1999). "Thioploca spp.: Filamentous sulfur bacteria with nitrate vacuoles". FEMS Microbiology Ecology. 28 (4): 301. doi:10.1111/j.1574-6941.1999.tb00585.x.
  3. ^ H. Fossing; V. A. Gallardo; B. B. Jørgensen; M. Hüttel; L. P. Nielsen; H. Schulz; D. E. Canfield; S. Forster; R. N. Glud; J. K. Gundersen; J. Küver; N. B. Ramsing; A. Teske; B. Thamdrup & O. Ulloa (2002). "Concentration and transport of nitrate by the mat-forming sulphur bacterium Thioploca". Nature. 374 (6524): 713–715. doi:10.1038/374713a0.
  4. ^ Gabe Paal (April 16, 1999). "Biggest bacteria ever found". EurekAlert!.
  5. ^ a b c d Jørgensen, Bo Barker; Teske, Andreas; Ahmad, Azeem (2015), "Thioploca", Bergey's Manual of Systematics of Archaea and Bacteria, John Wiley & Sons, Ltd, pp. 1–12, doi:10.1002/9781118960608.gbm01227, ISBN 978-1-118-96060-8, retrieved 2021-12-23
  6. ^ a b c d e Jørgensen, Bo Barker; Gallardo, Victor A (1999-04-01). "Thioploca spp.: filamentous sulfur bacteria with nitrate vacuoles". FEMS Microbiology Ecology. 28 (4): 301–313. doi:10.1111/j.1574-6941.1999.tb00585.x. ISSN 0168-6496.
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  36. ^ Whitman, William B; Rainey, Fred; Kämpfer, Peter; Trujillo, Martha; Chun, Jonsik; DeVos, Paul; Hedlund, Brian; Dedysh, Svetlana, eds. (2015-04-17). Bergey's Manual of Systematics of Archaea and Bacteria (1 ed.). Wiley. doi:10.1002/9781118960608.gbm01227. ISBN 978-1-118-96060-8.


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