Comparative genomics in "Candidatus Kuenenia stuttgartiensis" reveal high genomic plasticity in the overall genome structure, CRISPR loci and surface proteins.

BACKGROUND

Anaerobic ammonium oxidizing bacteria (anammox bacteria) are contributing significantly to the nitrogen cycle and are successfully used in wastewater treatment. Due to the lack of complete genomes in the databases, little is known about the stability and variability of their genomes and how the genomes evolve in response to changing environments.

RESULTS

Here we report the complete genome of the anammox bacterium "Candidatus Kuenenia stuttgartiensis" strain CSTR1 which was enriched planktonically in a semi-continuous stirred-tank reactor. A comparison of the genome of strain CSTR1 with the genome of "Ca. Kuenenia stuttgartiensis" MBR1 and the draft genome of KUST showed > 99% average nucleotide identity among all. Rearrangements of large genomic regions were observed, most of which were associated with transposase genes. Phylogenetic analysis suggests that strain MBR1 is more distantly related to the other two strains. Proteomic analysis of actively growing cells of strain CSTR1 (growth rate ~ 0.33 d) failed to detect the annotated cytochrome cd-type nitrite reductase (NirS) although in total 1189 proteins were found in the proteome. Yet, this NirS was expressed when strain CSTR1 was under stress or starvation (growth rate < 0.06 d). We also observed large sequence shifts in the strongly expressed S-layer protein compared to other "Ca. Kuenenia" strains, indicating the formation of hybrids of genes encoding the surface proteins.

CONCLUSIONS

"Ca. Kuenenia" strains appear to be relatively stable in their basic physiological traits, but show high variability in overall genome structure and surface proteins.