Biosynthesis of the 7-mercaptoheptanoic acid subunit of component B [(7-mercaptoheptanoyl)threonine phosphate] of methanogenic bacteria

Abstract It is generally recognized that reductive processes are more important than oxidative ones in transforming, degrading and mineralizing many environmental contaminants. One process of particular importance is reductive dehalogenation, i.e., the replacement of a halogen atom (most commonly a chlorine atom) by a hydrogen atom. A number of different mechanisms are involved in these reactions. Photochemical reactions probably play a role in some instances. Aliphatic compounds such as chloroethanes, partly aliphatic compounds such as DDT, and alicyclic compounds such as hexachlorocyclohexane are readily dechlorinated in the laboratory by reaction with reduced iron porphyrins such as hematin. Many of these are also dechlorinated by cultures of certain microorganisms, probably by the same mechanism. Such compounds, with a few exceptions, have been found to undergo reductive dechlorination in the environment. Aromatic compounds such as halobenzenes, halophenols and halobenzoic acids appear not to react with reduced iron porphyrins. Some of these however undergo reductive dechlorination both in the environment and in the laboratory. The reaction is generally associated with methanogenic bacteria. There is evidence for the existence of a number of different dechlorinating enzymes specific for different isomers. Recently it has been found that many components of polychlorinated biphenyls (PCBs), long considered to be virtually totally resistant to environmental degradation, may be reductively dechlorinated both in the laboratory and in nature. These findings suggest that many environmental contaminants may prove to be less persistent than was previously feared.

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Role of filter media in an anaerobic fixed-bed reactor

Water Science & Technology ◽

10.2166/wst.1995.0353 ◽

1995 ◽

Vol 31 (9) ◽

pp. 137-144 ◽

Cited By ~ 3

Author(s):

T. Miyahara ◽

M. Takano ◽

T. Noike

Keyword(s):

Anaerobic Bacteria ◽

Fixed Bed ◽

Methanogenic Bacteria ◽

The Other ◽

Fixed Bed Reactor ◽

Filter Media ◽

Fixed Bed Reactors ◽

Attached Bacteria ◽

The Relationship

The relationship between the filter media and the behaviour of anaerobic bacteria was studied using anaerobic fixed-bed reactors. At an HRT of 48 hours, the number of suspended acidogenic bacteria was higher than those attached to the filter media. On the other hand, the number of attached methanogenic bacteria was more than ten times as higher than that of suspended ones. The numbers of suspended and deposited acidogenic and methanogenic bacteria in the reactor operated at an HRT of 3 hours were almost the same as those in the reactor operated at an HRT of 48 hours. Accumulation of attached bacteria was promoted by decreasing the HRT of the reactor. The number of acidogenic bacteria in the reactor packed sparsely with the filter media was higher than that in the closely packed reactor. The number of methanogenic bacteria in the sparsely packed reactor was lower than that in the closely packed reactor.

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The bacterial numeration and an observation of a new syntrophic association for granular sludge

Water Science & Technology ◽

10.2166/wst.1997.0584 ◽

1997 ◽

Vol 36 (6-7) ◽

pp. 133-140 ◽

Cited By ~ 3

Author(s):

Zhu Jianrong ◽

Hu Jicui ◽

Gu Xiasheng

Keyword(s):

Anaerobic Bacteria ◽

Granular Sludge ◽

Methanogenic Bacteria ◽

Uasb Reactor ◽

Two Phase ◽

Methanogenic Activity ◽

Syntrophic Association ◽

Group I ◽

Acetogenic Bacteria ◽

Fermentative Bacteria

The bacterial numeration and microbial observation were made on granular sludge from laboratory single and two-phase UASB reactors. It was shown that the fermentative bacteria (group I), H2-producing acetogenic bacteria (group II) and methanogenic bacteria (group III) of granular sludge in single UASB reactor were 9.3 × 108−4.3 × 109, 4.3 × 107−4.3 × 108, 2.0−4.3 × 108, respectively, during the granulation process. The sludge of methanogenic reactor exhibited the similar results. That indicates there is no big difference between suspended and granular sludge, and bacterial population for three groups of anaerobic bacteria are similar. The formation of granular sludge depends mainly on the organization and arrangement of bacteria. An observation of granular sludge using electron microscope revealed that the fermentative bacteria and hydrogenotrophic methanogens existed on outer surface of granules, and aceticlastic methanogens and H2-producing acetogenic bacteria occupied the inner layer. A new syntrophic association between Methanosaeta sp. and Syntrophomonas sp. (even plus Methanobrevibacter sp.) was observed. Because Methanosaeta can effectively convert the acetate (the end product of propionate and butyrate) to methane, such a new syntrophic association is supposed to support the degradation of short fatty acids and high methanogenic activity of granular sludge. Based on structural pattern, a hypothesis on mechanism of granulation called “crystallized nuclei formation” is proposed.

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Effect of Short-Term Temperature Increase on the Performance of a Mesophilic UASB Reactor

Water Science & Technology ◽

10.2166/wst.1990.0081 ◽

1990 ◽

Vol 22 (9) ◽

pp. 183-190 ◽

Cited By ~ 17

Author(s):

J. B. van Lier ◽

J. Rintala ◽

J. L. Sanz Martin ◽

G. Lettinga

Keyword(s):

Sharp Decrease ◽

Methanogenic Bacteria ◽

Decay Rates ◽

Uasb Reactor ◽

Short Term ◽

Retention Capacity ◽

Temperature Shock ◽

Biomass Retention ◽

Propionate Oxidation ◽

Ph Decrease

A study was carried out to assess the effects of short-term temperature increments on the treatment efficiency and methane production of UASB reactors at a working temperature of 37-39°C. Two different substrates were used to determine the effects on the several bacterial groups involved in the digestion process. One reactor was fed with defined synthetic acidified wastewater the other with unacidified wastewaler from a distillery process. Shocks of 5-24 hrs were applied at temperatures in the range of 45 to 61°C. Up to 45°C no detrimental effects were noticeable. Higher temperatures led to a sharp decrease of the activity of the different microbial populations as a result of elevated decay rates. Propionate oxidation turned out to be the most sensitive for temperature increments, whereas the acidogenic bacteria were least affected. Temperature shocks of 55 and 61°C led to a decrease of 50% of the overall efficiency after 10 and 3 hrs, respectively. By means of batch experiments decay rates of 0.44 and > 10 hr −1 of the methanogenic bacteria were estimated at 55 and 65°C respectively. As temporary inactivation of the mesophilic bacteria during a temperature shock was found to be unlikely, reactor recovery is dependent on the bacterial growth and the biomass retention capacity of the reactor. When unacidified wastewater is treated, a pH decrease has to be considered during a temperature shock.

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