Characterization of the mitochondrial genome of Chlorolobion braunii ITBB-AG6, an azolla-associated green alga isolated from sanitary sewage

Abstract

Sphaeropleales have the characteristics of rapid growth, high oil content, and efficient removal rates of nitrogen and phosphorus in sewage waters, and is potentially valuable in biodiesel production and environmental remediation. In this study, we isolated a strain of Sphaeropleales, Chlorolobion braunii strain ITBB-AG6 from an azolla community in a sewage pond. Its mitochondrial genome contains 110,124 bp and harbors at least 40 genes, including 15 protein-coding genes, 20 tRNA genes, and three rRNA genes. The protein-coding genes include two for ATP synthases, seven for NAD(P)H-quinone oxidoreductases (nad), three for cytochrome c oxidase subunits (coxs), and one for cytochrome b (cob). Transfer RNA genes for 18 amino acids were identified, in which the tRNA genes for leucine and serine are doubled, but the tRNA genes for threonine and valine are not annotated. Phylogenetic analysis using the mitochondrial genomes of seven families of Sphaeropleales indicated that ITBB-AG6 is closely related to Monoraphidium neglectum, and falls in the family Selenastraceae with 100% bootstrap support. Two species in the family Neochloridaceae are separated by a species in Hydrodictyaceae, indicating a polyphyletic nature. These findings revealed the complicated phylogenetic relationships of the Sphaeropleales and the necessity of genome sequences in the taxonomy of microalgae.

Keywords:

• Chlorolobion braunii
• mitochondrial genome
• phylogenetic analysis
• organelle genome

Author contributions

He Yiliang performed genome assembly and annotation, Qiaoqiao Yang isolated the strain; Ma Shuai performed phylogenetic analysis, Jiaming Zhang analyzed the genome and wrote the draft, and Lai Hanggui took part in the identification of the strain and revision of the manuscript, and partially provided the funds for genome sequencing. All authors revised the manuscript and approved the final version of the manuscript.

Ethical approval

The study involved only a green alga, and was exempt from ethical approval.

Disclosure statement

The authors report there are no competing interests to declare.

Data availability statement

The genome sequence data that support the findings of this study are openly available in GenBank of the NCBI at https://www.ncbi.nlm.nih.gov under the accession no. OP778184. Raw reads generated by the authors to assemble this mitochondrial genome are available under GenBank BioProject no. PRJNA931121, BioSample no. SAMN33050851, and SRA no. SRR23329251.

Additional information

Funding

The work was supported by the Central Public-interest Scientific Institution Basal Research Fund for Chinese Academy of Tropical Agricultural Sciences [Grant No. 1630052020022].