The C. symbiosum cells were collected when the optical density (OD600) reached 1.0 by centrifugation (10,000 × g for 10 min) and then immediately frozen in liquid nitrogen. Next, genomic DNA was extracted by using a DNA extraction kit (Shandong Sparkjade Biotechnology Co., Ltd., China).
Genome sequencing was carried out using the Pacific Biosciences (PacBio) RS II sequencing platform. In brief, genomic DNA was sheared into ∼10 kb fragments using a Covaris g-TUBE shearing device (Covaris, Woburn, Massachusetts, USA). DNA fragments were purified, end-repaired, and ligated to SMRTParkbell hairpin adapters using the PacBio SMRTbell library preparation kit (Pacific Biosciences, Menlo Park, China, USA). SMRTbell DNA libraries were constructed according to the manufacturer's protocol (Pacific Biosciences, Menlo Park, CA, USA). The library quality analysis and quantification were determined using the Qubit 2.0 Fluorometer (Bio-Medlab, China) and the Agilent 2100 Bioanalyzer system (Agilent Technologies, SantaClara, CA, USA). The SMRT sequencing was accomplished using the PacBioRSII system (Pacific Biosciences, Menlo Park, CA, USA) according to the standard protocol. The obtained continuous PacBio long-reads generated from SMRT sequencing runs were adopted for de novo assembly using the program Spades (version 3.14.1), yielding one circular chromosome.
Genome sequencing was carried out using the Pacific Biosciences (PacBio) RS II sequencing platform. In brief, genomic DNA was sheared into ∼10 kb fragments using a Covaris g-TUBE shearing device (Covaris, Woburn, Massachusetts, USA). DNA fragments were purified, end-repaired, and ligated to SMRTParkbell hairpin adapters using the PacBio SMRTbell library preparation kit (Pacific Biosciences, Menlo Park, China, USA). SMRTbell DNA libraries were constructed according to the manufacturer's protocol (Pacific Biosciences, Menlo Park, CA, USA). The library quality analysis and quantification were determined using the Qubit 2.0 Fluorometer (Bio-Medlab, China) and the Agilent 2100 Bioanalyzer system (Agilent Technologies, SantaClara, CA, USA). The SMRT sequencing was accomplished using the PacBioRSII system (Pacific Biosciences, Menlo Park, CA, USA) according to the standard protocol. The obtained continuous PacBio long-reads generated from SMRT sequencing runs were adopted for de novo assembly using the program Spades (version 3.14.1), yielding one circular chromosome.