Polyphasic approach identifies two new species of Desmonostoc (Nostocales, Cyanobacteria) in the coralloid roots of Cycas fairylakea (Cycadales)

ABSTRACT

Endogenously formed coralloid roots in living cycads are known to be infected and maintained by a mutual partnership with photosynthetic cyanobacteria. In this study, two strains of filamentous, nitrogen-fixing endosymbiotic cyanobacteria from the green zone of the coralloid roots of Cycas fairylakea were isolated and grown in culture. The phylogenetic placement based on the 16S rRNA gene region and the secondary structures of the ITS between the 16S and 23S rRNA gene, in addition to traditional morphological characterization, were used to analyse the two strains. Results showed that the 16S rRNA gene sequences of the two strains, CF01 and CF06, displayed ≥97% similarity to the genus Desmonostoc. The phylogeny inferred by maximum likelihood, bayesian inference and neighbour-joining placed the two strains on a separate node away from other species of Desmonostoc. Hormogonial filaments were evident in the two symbiotic species. In addition, a few unique morphological structures in the CF01 and CF06 strains were observed. The D1-D1ʹ, Box-B and V3 helices generated from the ITS of 16S–23S sequences did not fit those of any described species of Desmonostoc, and this led to proposing the two strains as novel species. In compliance with the International Code of Nomenclature for algae, fungi, and plants, the two species are named Desmonostoc lechangense sp. nov. and Desmonostoc aggregatum sp. nov.

KEYWORDS:

• Desmonostoc aggregatum
• Desmonostoc lechangense
• Endosymbiotic cyanobacteria
• ITS secondary structure
• 16S rRNA gene

ACKNOWLEDGEMENTS

MHP thanks the CAS-TWAS President’s Fellowship for the doctoral scholarship and Mary Ann C. Bautista for her assistance in the construction of the phylogenetic tree. Thanks are also due to David E. Boufford for helping improve the manuscript.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

SUPPLEMENTARY MATERIAL

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Additional information

Funding

This research was supported by the National Forestry and Grassland Administration for Rescues and Breeding of Wild Rare and Endangered Species (Li N. 2017, 2018, 2019); Shenzhen Fairy Lake Botanical Garden for Metagenomics Studies on Microbial Diversity in the Coralloid Roots in Cycadales (Li N. FLSF-2020-02); Shenzhen Urban Management Bureau (Li N. 201411); Shenzhen Key Laboratory of Subtropical Plant Diversity, Fairy Lake Botanical Garden, Chinese Academy of Sciences (Chen T. 2017–2021).