Genomic Analysis of CZ1 Reveals Efficient Carbon Fixation Modules.

Cyanobacteria, one of the most widespread photoautotrophic microorganisms on Earth, have evolved an inorganic CO-concentrating mechanism (CCM) to adapt to a variety of habitats, especially in CO-limited environments. , a filamentous cyanobacterium, is widespread in a variety of environments and is well adapted to low-inorganic-carbon environments. However, little is currently known about the CCM of , in particular its efficient carbon fixation module. In this study, we isolated and purified the cyanobacterium CZ1 from the Xin'anjiang River basin and identified it as by 16S rRNA sequencing. Genome analysis revealed that CZ1 contains β-carboxysome shell proteins and form 1B of Rubisco, which is classify it as belonging to the β-cyanobacteria. Further analysis revealed that CZ1 employs a fine CCM involving two CO uptake systems NDH-1 and NDH-1, three HCO transporters (SbtA, BicA, and BCT1), and two carboxysomal carbonic anhydrases. Notably, we found that NDH-1 and NDH-1 are located close to each other in the CZ1 genome and are back-to-back with the operon, which is a novel gene arrangement. In addition, CZ1 encodes two high-affinity Na/HCO symporters (SbtA1 and SbtA2), three low-affinity Na-dependent HCO transporters (BicA1, BicA2, and BicA3), and a BCT1; it is rare for a single strain to encode all three bicarbonate transporters in such large numbers. Interestingly, CZ1 also uniquely encodes two active carbonic anhydrases, CcaA1 and CcaA2, which are also rare. Taken together, all these results indicated that CZ1 is more efficient at CO fixation. Moreover, compared with the reported CCM gene arrangement of cyanobacteria, the CCM-related gene distribution pattern of CZ1 was completely different, indicating a novel gene organization structure. These results can enrich our understanding of the CCM-related gene arrangement of cyanobacteria, and provide data support for the subsequent improvement and increase in biomass through cyanobacterial photosynthesis.