Genomic Insights into Two Novel Fe(II)-Oxidizing Zetaproteobacteria Isolates Reveal Lifestyle Adaption to Coastal Marine Sediments

摘要

The discovery of the novel Zetaproteobacteria class greatly expanded our understanding of neutrophilic, microaerophilic microbial Fe(II) oxidation in marine environments. Despite molecular techniques demonstrating their global distribution, relatively few isolates exist, especially from low-Fe(II) environments. Furthermore, the Fe(II) oxidation pathways used by Zetaproteobacteria remain poorly understood. Here, we present the genomes (>99 genome completeness) of two Zetaproteobacteria, which are the only cultivated isolates originating from typical low-Fe porewater Fe(II), 70 to 100 mu M coastal marine sediments. The two strains share <90 average nucleotide identity (ANI) with each other and <80 ANI with any other Zetaproteobacteria genome. The closest relatives were Mariprofundus aestuariurn strain CP-5 and Mariprofundus ferrinatatus strain CP-8 (96 to 98 16S rRNA gene sequence similarity). Fe(II) oxidation of strains KV and NF is most likely mediated by the putative Fe(II) oxidase Cyc2. Interestingly, the genome of strain KV also encodes a putative multicopper oxidase, PcoAB, which could play a role in Feat) oxidation, a pathway found only in two other Zetaproteobacteria genomes (Ghiorsea bivora TAG-1 and SCGC AB-602-C20). The strains show potential adaptations to fluctuating O-2 concentrations, indicated by the presence of both cbb(3)- and aa(3),-type cytochrome c oxidases, which are adapted to low and high O-2 concentrations, respectively. This is further supported by the presence of several oxidative-stress-related genes. In summary, our results reveal the potential Fe(II) oxidation pathways employed by these two novel chemolithoautotrophic Fe(II)-oxidizing species and the lifestyle adaptations which enable the Zetaproteobacteria to survive in coastal environments with low Fe(II) and regular redox fluctuations.