Zetaproteobacteria

[1][3] Molecular cloning techniques focusing on the small subunit ribosomal RNA gene have also been used to identify a more diverse majority of the Zetaproteobacteria that have as yet been unculturable.

[4] Regardless of culturing status, the Zetaproteobacteria show up worldwide in estuarine and marine habitats associated with opposing steep redox gradients of reduced (ferrous) iron and oxygen, either as a minor detectable component or as the dominant member of the microbial community.

[16] Subsequent isolation of two strains of M. ferrooxydans, PV-1 and JV-1,[3] along with the increasing realization that a phylogenetically distinct group of Pseudomonadota (the Zetaproteobacteria) could be found globally as dominant members of bacterial communities led to the suggestion for the creation of this new class of the Proteobacteria.

[3][20] Oxidized, or ferric, iron is insoluble at circumneutral pH, thus the microbe must have a way of dealing with the mineralized "waste" product.

[21][22][23] Some of the most common morphotypes include: amorphous particulate oxides, twisted or helical stalks (figure),[21] sheaths,[24] and y-shaped irregular filaments.

(twisted stalk) and Leptothrix ochracea (sheath) have only extremely rarely been found in the deep sea (not significant abundance).

In microbial ecology, the small subunit ribosomal RNA gene is generally used at a cut off of 97% similarity to define an OTU.

In recent years, researchers have made progress in suggesting possibilities for how the Zetaproteobacteria oxidize iron, primarily through comparative genomics.

Identifying the iron oxidation pathway in the Zetaproteobacteria began with the publication of the first described cultured representative, M. ferrooxydans strain PV-1.

[67] In a follow-up analysis of a metagenomic sample, Singer et al. (2013) concluded that this molybdopterin oxidoreductase gene cassette was likely involved in Fe oxidation.

[70] The phylogenetic distance between the Zetaproteobacteria and the Fe-oxidizing freshwater Betaproteobacteria suggests that Fe oxidation and the produced biominerals are the result of convergent evolution.

[24] Comparative genomics has been able to identify several genes that are shared between the two clades, however, suggesting that the trait of Fe oxidation could have been horizontally transferred, possibly virally mediated.