Synthetic Biology and the Possibilities in Achieving a Plant …
127
Fig. 7 A denitrifying genetic P. denitrificans construct, in which with synthetic biological methods
genes from N. europaea are introduced. The system consists of a promotor at the beginning (black
arrow), the ribosomal binding sites (green) the amo-operon (AmoA, AmoB, AmoC), and the genes
Cc554, Ccm552 and HAO [52]
under anaerobic conditions [58]. Another promising candidate for future improving
SND is Thiosphaera pantotropha (T. pantotropha). T. pantotropha is able to perform
nitrification, denitrification and fix CO 2 with the special characteristic to be able to
grow on a wide range of substrates as sulfur compounds or hydrogen. According
to high growth rates, T. pantotropha is an attractive bacterium for efficient wastewater treatment [42]. Further characterization of the enzymes that are involved in the
metabolic pathway and redesigning the properties by means of synthetic biology
would make T. pantotropha the perfect chassis for SND (Fig. 7).
5 The Anammox Process
Certain planctomycetes were discovered in the early 1990s in wastewater sludge,
which can oxidize ammonium with NO
−
2 to dinitrogen gas [74]. This process is called
anaerobic ammonium oxidation (anammox), which led to the term anammox bacteria
for bacteria capable of performing this reaction. Some representatives of anammox
bacteria are “Candidatus Kuenenia”, “Candidatus Brocadia”, “Anammoxoglobus”,
“Candidatus Jettenia” [47, 102]. During the anammox reaction, nitrite serves as
electron acceptor and is reduced at first to nitric oxide. From the nitric oxide and
ammonium as electron donor, the biosynthesis of hydrazine occurs, which is then
further converted into dinitrogen gas via dehydration [56, 76]. The process thereby
takes place in the so called anammoxosome, a membrane-bound intracytoplasmic
cellular compartment [103]. Due to the ability to oxidize ammonium with nitrate or
nitrite anaerobically, the anammox bacteria supplement the common nitrate cycle.
These potentials also qualify the bacteria as promising candidates for improving
wastewater treatment. In aerated wastewater treatment reactors or in aerated soils,
fertilized with nitrate, anammox bacteria in combination with heterotrophic denitrifying bacteria and archaea can help reducing the biological oxygen demand (BOD)
and enhancing organic carbon degradation [48]. Thereby, synthetic biology may
further improve the procedure. For instance, Nitrosomonas europaea, a prevailing
ammonia oxidizing bacterium, could be converted to a planctomycete lineage that
grows well in synthetic medium with bicarbonate as only carbon source or in wastewater treatment reactors [88, 94, 101]. In general, anammox planctomycetes occur in a
high number in freshwater samples and molecular biologically analysed wastewaters
127
Fig. 7 A denitrifying genetic P. denitrificans construct, in which with synthetic biological methods
genes from N. europaea are introduced. The system consists of a promotor at the beginning (black
arrow), the ribosomal binding sites (green) the amo-operon (AmoA, AmoB, AmoC), and the genes
Cc554, Ccm552 and HAO [52]
under anaerobic conditions [58]. Another promising candidate for future improving
SND is Thiosphaera pantotropha (T. pantotropha). T. pantotropha is able to perform
nitrification, denitrification and fix CO 2 with the special characteristic to be able to
grow on a wide range of substrates as sulfur compounds or hydrogen. According
to high growth rates, T. pantotropha is an attractive bacterium for efficient wastewater treatment [42]. Further characterization of the enzymes that are involved in the
metabolic pathway and redesigning the properties by means of synthetic biology
would make T. pantotropha the perfect chassis for SND (Fig. 7).
5 The Anammox Process
Certain planctomycetes were discovered in the early 1990s in wastewater sludge,
which can oxidize ammonium with NO
−
2 to dinitrogen gas [74]. This process is called
anaerobic ammonium oxidation (anammox), which led to the term anammox bacteria
for bacteria capable of performing this reaction. Some representatives of anammox
bacteria are “Candidatus Kuenenia”, “Candidatus Brocadia”, “Anammoxoglobus”,
“Candidatus Jettenia” [47, 102]. During the anammox reaction, nitrite serves as
electron acceptor and is reduced at first to nitric oxide. From the nitric oxide and
ammonium as electron donor, the biosynthesis of hydrazine occurs, which is then
further converted into dinitrogen gas via dehydration [56, 76]. The process thereby
takes place in the so called anammoxosome, a membrane-bound intracytoplasmic
cellular compartment [103]. Due to the ability to oxidize ammonium with nitrate or
nitrite anaerobically, the anammox bacteria supplement the common nitrate cycle.
These potentials also qualify the bacteria as promising candidates for improving
wastewater treatment. In aerated wastewater treatment reactors or in aerated soils,
fertilized with nitrate, anammox bacteria in combination with heterotrophic denitrifying bacteria and archaea can help reducing the biological oxygen demand (BOD)
and enhancing organic carbon degradation [48]. Thereby, synthetic biology may
further improve the procedure. For instance, Nitrosomonas europaea, a prevailing
ammonia oxidizing bacterium, could be converted to a planctomycete lineage that
grows well in synthetic medium with bicarbonate as only carbon source or in wastewater treatment reactors [88, 94, 101]. In general, anammox planctomycetes occur in a
high number in freshwater samples and molecular biologically analysed wastewaters