Heterotrophic denitrifiers

The system operates anaerobically and at near neutral pH, employing anaerobic Thiobacil-lus cultures in consortium with heterotrophic denitrifying cultures. The denitrifying population... 

The heterotrophic nitrifier mentioned earlier, P. pantatrophus, carries out at least part of both processes under aerobic conditions. P. pantatrophus was originally isolated from wastewater and its ability to denitrify aerobically, as well as this abifity in several other conventional heterotrophic denitrifiers, has been confirmed (Robertson et al, 1995). 

Nearly all heterotrophic denitrifiers are facultative anaerobes (Tiedje, 1988). Although various workers defined suboxia differently, the upper limit of oxygen concentration for the occurrence of denitrification is probably 5 pM, with quantitatively most denitrification in the marine environment taking place below about 2 pM (Cline and Richards, 1972 Codispoti et al., 2005 Devol, 1978 Murray et al., 1995). The ability to denitrify is not limited to the bacteria, archea and even some fungi are capable of denitrification (Knowles, 1996 Zumft and Korner, 1997). 

Thiobacillus denitrificans is well known as a lithoautotrophic denitrifier it oxidizes anaerobically thiosulfate (S2032 ) with nitrate (N03 ) to biosynthesize ATP although it also aerobically oxidizes thiosulfate (Aminuddin and Nicholas, 1973, 1974a) (Fig. 1.9). The anaerobic oxidation system of thiosulfate is similar to those of other thiobacilli (though these are aerobic bacteria), and the denitrifying processes in the bacterium are similar to those in the heterotrophic denitrifiers. The complete genome of the bacterium has recently been sequenced (Beller et al., 2006). 

Some prokaryotes are anaerobic heterotrophs. These include the denitrifiers, sulfate reducers, and fermenters, as well as the bacteria capable of reducing metals, such as Fe(lll) to Fe(II) and Mn(lV) to Mn(II). Because the oxidized metals are present as solids, e.g., FeOOH(s), Fe203(s), and Mn02(s), these bacteria must be in direct contact with the mineral surface and have a mechanism for transferring electrons across their cell membranes. One bacterium that appears to have such a mechanism is the facultative anaerobe Shewanella oneidensis, which produces a specific protein on its outer membrane only under anaerobic conditions when it is in direct contact with a suitable... 

After the nitrogen has been nitrified, the second unit process of denitrification is then applied. The denitrifying bacteria, which are actually heterotrophs, convert the nitrates into nitrogen gas, thus ridding the wastewater of nitrogen. Denitrification is an anaerobic process. 

It has been argued that heterotrophic nitrification involves enzyme systems that are quite different from those of the autotrophs (Wehrfritz et al, 1993) and that heterotrophic nitrification cannot serve as an energy generating mechanism (Castignetti, 1990), as the autotrophic process does. In the aerobic denitrifiers, which are also capable of nitrification, the initial enzyme, AMO, appears to be quite similar to the enzyme in autotrophic nitrifiers. However, HAO differs significantly and in the heterotrophs, is a smaller, simpler enzyme that performs a two electron transfer (instead of the four electron transfer of the autotrophic HAO) and... 

Thermophilic heterotrophic nitrifiers, capable of oxidizing NH3 to N02, were isolated from several hydrothermal vent habitats (Mevel and Prieur, 1998). Most of the isolates were N03 reducers or denitrifiers and exhibited a wide diversity related to the genera Thermus and Bacillus. Because they are able to ammonify, nitrify and reduce N03, they would seem to possess most of the physiologies of importance in the N cycle. Such organisms may be common in mesophilic aquatic habitats, but have not been quantitatively investigated. 

Castignetti, D. (1990). Bioenergetic examination of the heterotrophic nitrifier-denitrifier Thiosphaera pantotropha. Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology 58, 283-289. 

In the Baltic-North Sea transition smdy of Thamdrup and Dalsgaard (2002), anammox contributed 33-67% of total N2 production at continental shelf sites, but just 2% of total N2 production at the site in a coastal bay (Figure 16). The difference between the bay site and the closest continental shelf site was due primarily to an increase in the denitrification rate, rather than a decrease in anaerobic oxidation. Denitrification declined in parallel with declining sediment organic carbon content from the coastal bay seaward. Absolute rates of anaerobic NH4 oxidation were in the range 30-99 p.M d and were lowest at the site where the percent contribution was highest. This pattern is consistent with evidence that anammox organisms are autotrophic, whereas denitrifiers are heterotrophic. 

Populations of heterotrophs (both aerobic and anaerobic) were determined by a cultivation method on the nutrient agar with 7 day incubation at 26 C. The ammonifying, nitrifying and denitrifying bacteria, as well as those oxidizing hydrocarbons were determined on liquid media as a most probable number. The ammonifying bacteria were determined on nutrient broth by employing the... 

Castelfranco PA, Walker CJ, Weinstein JD (1994) Biosynthetic studies on chlorophylls from protoporphyrin IX to protochlorophyllide. In The biosynthesis of the tetrapyrrole pigments (Ciba Foundation Symposium 180). Wiley, Chichester, pp 194-204 Castignetti D, Hollocher TC (1982) Nitrogen redox metabolism of a heterotrophic, nitrifying-denitrifying Alcaligenes sp. from soil. Appl Environ Microbiol 44 923-928... 

Heterotroph (=chemoonganotroph) Oxidation of organic compounds Org. C (max. 30% CO2) Org. C Anaerobic Denitrifying bacteria Mn- or Fe-reducing bacteria Sulfate reducing bacteria Fermenting bacteria... 

The heterotrophic soil bacteria include nitrogen-fixing bacteria and the denitrifying bacteria that will be discussed later. 

The denitrifying bacteria deserve special mention because of their practical importance. They are chiefly mesophilic heterotrophs that commonly grow aerobically on various carbon sources but can also grow anaerobically if supplied with nitrate that serves as a hydrogen acceptor in place of oxygen. In the process of utilization of the nitrate they... 

From the previously reviewed literature, it can be concluded that the sequence of e-acceptor use found in sediments is also present in biofilms. This was almost comprehensively demonstrated with microsensors in wastewater biofilms (De Beer 1999). First, O2 is used by heterotrophic and autotrophic processes (nitrification and sulfide oxidation). Then NO2 and NOs, formed by nitrification or originating from the water phase, are consumed in the zone directly adjacent to the oxic layer. Denitrification can be coupled to sulfide oxidation. Sulfate reduction is found below the denitrifying zone. Methanogenesis is also spatially separated from sulfate reduction and occurs in the deepest zones of the hiofihns. 

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