Desulfuromonadales

The Desulfuromonadales form an order within the Deltaproteobacteria. Like all Proteobacteria, they are gram - negative. Use by anaerobic respiration of elemental sulfur, manganese or iron to produce energy in metabolism. One speaks of the Fe ( III) -, sulfur or Mn ( IV ) reduction. Also, nitrate and trichloroacetic acid, as well as other metals such as technetium or cobalt can be reduced by some of these bacteria and thus used in energy metabolism.

The species of this order are mostly rod -shaped. Most of them are mobile Pelobacter and Malonomonas by a scourge but only in the early stages of growth of the colonies, others are motionless.

Properties

The members of this order are mostly obligate anaerobic, meaning they can only in the complete absence of oxygen to live, but there are some micro-aerobic species. For example tolerated Malonomonas low oxygen concentrations. Desulfuromusa kysingii is also slightly oxygen- tolerant, but does not grow under the influence of oxygen. Most Desulfuromonadales are mesophilic, ie their growth optimum is at intermediate temperatures. Geopsychrobacter is psychrophilic ( cold- loving), it grows at temperatures 4-30 ° C, the optimum is at 22 ° C. Geothermobacter ehrlichii is thermophilic and was found in a hydrothermal source of the Juan de Fuca Ridge. It grows at temperatures between 35 and 65 ° C.

Desulfuromonadales were anoxic Habiten in fresh water, sea water and brackish water isolated. Malonomonas occurs in anoxic marine sediments, in fresh water, this genus has not been found. Geobacter seem floors to play the predominant role in the Fe ( III) - reducing bacteria.

Ecology

Some types of Desulfuromonas can live in the presence of acetate in a mutualistic association with species of phototrophic sulfur bacteria forming the green sulfur bacteria ( Chlorobiaceae ). In this Syntrophismus of energy metabolism and thus the growth of both partners through the exchange of certain metabolites is promoted each other. For example, the green sulfur bacterium forms Prosthecochloris aestuarii of hydrogen sulfide elemental sulfur ( S0) from which Desulfuromonas again, as long as acetate is present, formed by sulfate reduction sulfide ( H2S). Thus, a condensed sulfur cycle forms.

By the reduction of trivalent iron ions (Fe3 ) to the divalent ( Fe2 ) or elemental sulfur to hydrogen sulfide Desulfuromonadales play an important role in the sulfur cycle and iron circuit of the earth. Further iron - reducing bacteria be of interest in relation to evolution. It is believed that the Fe (III ) reduction in addition to the sulfur reduction is one of the first of the anaerobic respiration of bacteria. One finds this form of metabolism, especially in the early branching lineages of bacteria and archaea.

Some Geobacter strains are significant due to their ability to degrade aromatic compounds such as toluene, for cleaning of contaminated soils and groundwater.

Geobacter metallireducens may be used as the electron acceptor also uranium: the form of the uranyl ion ( UO22 ), water-soluble hexavalent uranium U ( VI), in this case by the bacterial transfer of two electrons to tetravalent uranium U ( IV ) is reduced, which in turn, as the water-insoluble uranium dioxide (UO2, the mineral uraninite ) fails. Thus, this bacterium for the cleanup of contaminated water with uranium is applicable.

Metabolism

Energy sources of these bacteria are anaerobic respiration and fermentation order. In the anaerobic respiration of Desulfuromonadales elemental sulfur (S0), polysulphides or trivalent iron (Fe3 ) instead of oxygen (such as in the aerobic respiration) in the respiratory chain are used as electron acceptors, thereby reducing. As electron donors are simple organic compounds such as B acetate. The energy released is used for ATP formation. The organic electron donors are usually completely oxidized via the citric acid cycle to CO2. In the sulfur reduction ( sulfur respiration ) of sulfur is reduced to hydrogen sulfide (H2S ) in the reduction of iron (iron breathing) trivalent iron ions (Fe3 ) to the divalent ( Fe 2 ). Other materials can be reduced, for example, manganese (IV), cobalt, technetium, nitrate and trichloroacetic acid.

The phylogenetic relationship of the iron ( III) - and manganese ( IV) - reducing bacteria is diverse. Many of these bacteria, which in this case completely oxidize acetate, can be found in the Geobacteraceae. Others with this property are such as species of Shewanella ( Gammaproteobacteria ), Acidithiobacillus ferrooxidans ( Betaproteobacteria ) and Deferribacter themophilus ( Deferribacteres ).

Manganese ( IV) -, iron ( III) - and sulfate reduction are used exclusively for energy production, not the change in building materials, such as for the construction of amino acids, so are not assimilationist, the end products, Mn ( II ), Fe (II ) or. hydrogen sulfide are excreted immediately.

Sulfur reduction

All species of Geobacter sulfurreducens and Desulfuromonadaceae, Geobacter humireducens and Pelobacter carbinolicus among the Schwefelatmern. At Pelobacter carbinolicus sulfur as well as the iron reduction was detected. Simple organic compounds such as acetate are used as electron donors in energy metabolism and as a building material sources. More usable for various kinds substances include: glutamate, fumarate, alanine, oxaloacetate and pyruvate. Desulfuromonas palmitatis oxidized inter alia, long-chain fatty acids. Besides, it can also use elemental, molecular hydrogen H2 in energy metabolism as an electron donor.

Desulfuromonas acetoxidans reduced elemental sulfur to hydrogen sulfide and uses acetate as an electron donor, which is oxidized via the citric acid completely to carbon dioxide (CO2):

In English, we also speak of the "sulfur reducing bacteria". The prefix desulfur - in systematics stands for sulfur reduction. In the sulfur respiration of these bacteria sulfate, thiosulfate and sulfite are not used as electron acceptors. This differs from the Sulfatatmern ( sulfate-reducing bacteria). Some sulfate reducers ( Sulfatatmer ), however, are also able to use elemental sulfur as an electron acceptor.

Some other known bacteria that reduce elemental sulfur are: Desulfovibrio gigas types of Desulfomicrobium, and Wolinella succinogenes Desulfurella acetivorans. Sulfur -reducing archaea are: ambivalens Sulfolobus, Pyrobaculum islandicum, Stygiolobus azoricus and Thermodiscus maritimus.

Iron reduction and other electron acceptors

Iron is widely distributed in nature and is an important metabolic element that was used early in the course of evolution for the energy metabolism. Many species of the order Desulfuromonadales reduce Fe3 to Fe2 . The iron ( III) ions can be removed from various iron compounds, some examples are: iron ( III) chloride, iron ( III) oxide and iron ( III ) citrate. Geobacter metallireducens reducing Fe (III) to Fe ( II) acetate with, for example, as the electron donor:

All kinds of Geobacter, Geothermobacter and Geopsychrobacter and Pelobacter carbinolicus, P. and P. acetylenicus venetianus use ferric iron (Fe3 ) as an electron acceptor. Many types of Desulfuromonadaceae use except sulfur and iron as an electron acceptor.

In Desulfuromusa kysingii and in some species of Geobacter (eg Geobacter metallireducens and Geobacter humireducens ) and nitrate can serve as an electron acceptor. Nitrate is reduced to ammonia, and not elemental, molecular nitrogen, N2, as is the case with the denitrification.

Manganese is also of some species, such as: palmitatise Desulfuromonas, Geobacter metallireducens and Desulfuromonas acetexigens, reduced and used as an electron acceptor. Mn ( IV) is in this case reduced to Mn (II). Trichlorobacter ( Geobacteraceae ) uses trichloroacetic acid as an electron acceptor and reduce it to dichloroacetic acid and hydrogen chloride (HCl). There is a relatively large variety of metals, which are reduced by some species in energy metabolism, such as cobalt Co ( III) and technetium Tc ( VII) from Geobacter sulfurreducens. Tc ( VII) is also used by Geobacter metallireducens as an electron acceptor. Whether the Tc (VII ) reduction in this case also allows the growth of these species, however, is unclear. Even uranium U ( VI) can be used by Geobacter metallireducens as the sole electron acceptor and is reduced to U ( IV). This bacterium grows when U (VI) is present as a single electron. Shewanella putrefaciens Also, a bacterial species of Gammaproteobacteria, shows that ability. In other Fe (III) - and manganese ( IV) as well as in many Atmern sulfate - reducing bacteria (for example, Desulfovibrio ) also has been demonstrated the ability to reduce U (VI), but growth is not observed.

Fermentation

Some members of the Desulfuromonadales are also capable of fermentation ( to distinguish the term fermentation qv). As a rule, acetate is the end product. All kinds of Desulfuromusa can use this energy metabolism in addition to anaerobic respiration. Also, all members of the Pelobacteraceae are capable of fermentation. Here also, in addition to ethanol acetate formed ( Pelobacter acetylenicus, P. and P. carbinolicus venetianus ) propionicus in P. also propionate. P. acidigallici forms acetate and CO2. Malonomonas can be cultured on an agar medium with malonate as sole energy and carbon source, formed here from malonate acetate as a final product, malate and fumarate may also be used of this type, the final products are then succinate and CO2.

History

The sulfur reduction, acts as an electron donor in the acetate, was not discovered until 1976 by ​​the bacterium Desulfuromonas acetoxidans. Geobacter metallireducens was isolated in 1987 by Lovley and colleagues from sediments of the Potomac River and is referred to as bacterial strain GS -15. 1988 be energy metabolism was with complete oxidation of acetate (and other carbon compounds ), associated with Fe (III ) reduction detected and 1993, the bacterium was identified as Geobacter metallireducens.

Geobacter metallireducens is an intensely investigated Eisenreduzierer and is, inter alia, of particular interest to the Geomicrobiology and especially the study of the metabolic pathway of iron reduction.

System

The order Desulfuromonadales consists of the following families and genera:

• Desulfuromonadaceae Corrig. Küver et al. 2006 Desulfuromonas Pfennig & Biebl 1977
• Desulfuromusa Liesack & Finster 1994

• Geobacteraceae Holmes et al. 2004 Geoalkalibacter Zavarzina et al. 2007
• Geobacter Lovley et al. 1995 Geobacter sulfurreducens Caccavo et al. 1994

• Pelobacteraceae Malonomonas Dehning & Schink 1990
• Pelobacter Schink & Pfennig 1983

A further, older but still used system consists of only two families:

• Desulfuromonadaceae Desulfuromonas
• Desulfuromusa
• Malonomonas
• Pelobacter

• Geobacteraceae Geoalkalibacter Zavarzina et al. 2007
• Geobacter
• Geopsychrobacter
• Geothermobacter
• Trichlorobacter

Swell