Genotypic and molecular characterization of a moderately thermophilic cyanobacterium, Gloeocapsa sp. strain BRSZ

Abstract

A unicellular-colonial cyanobacterium, designated “BRSZ,” was isolated from a neutral-alkaline hot spring in Thailand. Morphological characterization revealed distinctive features consistent with those of the genus Gloeocapsa. Physiological assessments demonstrated that BRSZ is a moderately thermophilic and halotolerant cyanobacterium with the potential for chemoheterotrophic growth in dark conditions. Molecular phylogenetic analysis based on 16S ribosomal RNA (rRNA) gene sequences placed BRSZ within a well-defined Gloeocapsa clade, a finding corroborated by 16S-23S internal transcribed spacer (ITS) rRNA secondary structure analyses. Genome comparisons, including average nucleotide identity (ANI), genome-to-genome distance (GGD), and digital DNA-DNA hybridization (dDDH), between strain BRSZ and closely related taxa showed an ANI value of 95.45 %, near the lower boundary of the species delineation threshold (95-96 %). A GGD of 0.0374 (>0.0258) and dDDH of 69 % (<70 %) further supported genomic differentiation. Genome-based analysis revealed a mycosporine-like amino acid biosynthetic gene cluster likely involved in sunscreen compound production. Cultivation-based production of a UV-absorbing compound confirmed the functional relevance of this gene cluster. These findings expand the described diversity within the Gloeocapsa complex and enhance our understanding of the taxonomy of this group. In addition, they underscored the importance of hot spring environments as sources of novel extremophiles.

Keywords

Polyphasic taxonomy / Unicellular cyanobacteria / Gloeocapsa / Extremophile / Thermophile / Heterotrophy / Hot spring

Data Availability Statement

The data supporting the findings of this study are included in this published article as well as in the Supplementary Materials available online.

Declaration of Competing Interes

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement

Sasiprapa Samsri: Writing - original draft, Formal analysis. Tanwalee Deprom: Investigation. Chananwat Kortheerakul: Investigation. Sophon Sirisattha: Investigation. Stephen B. Pointing: Writing - review & editing, Funding acquisition, Conceptualization. Hakuto Kageyama: Writing - review & editing, Funding acquisition, Conceptualization. Rungaroon Waditee-Sirisattha: Writing - review & editing, Funding acquisition, Conceptualization.

Acknowledgments

We thank our lab members for their technical support. This work was supported in part by the following research grants: Thailand Science research and Innovation fund Chulalongkorn University (FOOD_FF_68_121_2300_022) (to RWS), the Singapore Ministry of Education MOE-T2EP30123-0007 (to RWS & SBP), the Research Institute of Meijo University (to HK), and Postdoctoral Fellowship, the Second Century Fund (C2F), Chulalongkorn University (to SS).

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