2.2.3 Illumina sequencing
Specific primers with the barcode or fusion primers with dislocation of the bases were synthesized according to the designated sequencing regions. The primers for cbbL , cbbM and nifH were 595F/1387R, 490F/974R and PolF/PolR, respectively. A TransGen AP221-02: TransStart FastPfu DNA polymerase 20 μL reaction system was used (Alfreider, Vogt, Hoffmann & Babel 2003; Tourova, Kovaleva, Sorokin & Muyzer, 2010; Shao et al., 2019; Xu et al., 2020; Yue et al., 2020).
Data availability: The complete sequencing data sets have been deposited in the NCBI Sequence Read Archive (SRA) database under the accession number PRJNA555455.