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Safari File Edit View History Bookmarks Window Help session.masteringmicrobiology.com Microbiology Now: New Discoveries Have Redefined the Global Nitrogen Cycle 1 of 17> Nitrification, the aerobic oxidation of ammonia to nitrate, is a critical component of the global nitrogen cycle and is mediated exclusively by microorganisms. The Russian microbiologist Sergei Winogradsky was the first to descnbe the microbial basis of nitrification when he isolated chemolithotrophic bacteria that the process of nitrification has been considered a two-step p chemolithotrophs: (1) microbes that oxidizing Bacteria and Archaea typically associate closely with n nitrification absolutely required the coordinated activities of both of these functional groups. That is, only by working together could these microbes catalyze the overall nitrification process. oxidized ammonia to nitrite over a century ago. Since then, rocess that requires two physiological classes of oxidize ammonia to nitrite, and (2) microbes that oxidize nitrite to nitrate. Ammonia- trite-oxidizing Bacteria, and it has long been thought that continue to redefine our understanding of the nitrogen cycle, and sometimes these discoveries come rowing in an oil well. This biofilm was used to inoculate an from unexpected sources, such as a microbial biofilm found g enrichment culture designed to grow nitrifying bacteria. Over time the culture was found to oxidize ammonia all the way to nitrate, but the microbes in this culture did not match any known nitrifying organisms. Since the bacteria could not be gr in isolation, metagenomic sequencing was used to reconstruct the genomes of the species present. One of the dominant genomes belonged to the phylum Nitrospira (the photo shows clusters of fluorescently stained Nitrospira cells 3D reconstruction of a biofilm observed by contocal laser microscopy). Bacteria from this phylum were already known to oxidize nitrite to nitrate (the second step of nitrification), but this microbe was different. It also contained the genes required for ammonia oxidation, most notably the gene encoding the key enzyme ammonia monooxygenase. [yellow) in a This novel bacterium, named Candidatus Nitrospira inopinata, is the first microbe shown to perform both steps of nitrification. n identified, unique gene sequences from these complete ammonia-oxidizing bacteria-nicknamed comammox' bacteria for their dual metabolic activities-have been found in freshwater, soil, and engineered environments worldwide. The discovery of comammox bacteria once again emphasizes the fact that new microbial metabolisms are typically just "one culture away

Explanation / Answer

Part A

Most oxidized to Most reduced

(SO4)2- > (S2O3)2- > (S0) > H2S

The oxidation number of sulfur in (SO4)2- is +6

The oxidation number of sulfur in (S2O3)2- is +2

The oxidation number of sulfur in (S0) is 0

The oxidation number of sulfur in H2S is -1

Part B

Nitrification: Involves the steps involved in the oxidation of ammonia to nitrate

The second step of nitrification: Involves the oxidation of NO2- to NO3-

Commommox: describes bacteria with the enzymes for both steps of nitrification

The first step of nitrification: Involves the oxidation of ammonia to nitrate

Denitrification: Involves the steps involved in the reduction of nitrate to ammonia

Ammonia monooxygenase is responsible for the enzyme catalyzing the reaction that converts NH3 to hydroxylamine.

Part C

Nitrogen fixation - Obligate anaerobes

Nitrification: Chemolithotrophs, Chemoorganotrophs, microbes that oxidize inorganic nitrogen compounds

Denitrification: Facultative anerobes, obligate aerobes

Part D

Monooxygenase adds oxygen to the substrate and causes oxidation. So, methane monooxygenase causes oxidation of methane by adding oxygen.

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