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<p>Zooplankton in the Southern Ocean represent unique microhabitats for microbial communities that contribute significantly to polar biogeochemical cycles. In this study, we performed a polyphasic and genomic characterization of two Gram-negative, psychrotolerant bacterial strains, HL-MZ7<sup>T</sup> and HL-MZ19, isolated from Antarctic zooplankton. Phylogenetic and phylogenomic analyses clearly placed these isolates within the genus <i>Pseudocolwellia</i>, forming a sister clade to <i>Pseudocolwellia agarivorans</i> QM50<sup>T</sup>. The complete genomes of HL-MZ7<sup>T</sup> (4.5 Mbp) and HL-MZ19 (4.6 Mbp) exhibited DNA G + C contents of 36.0% and 35.9%, respectively. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values confirmed that both strains represent a novel genomic species, distinct from <i>P. agarivorans</i> QM50<sup>T</sup> (79.5% ANI and 24.0% dDDH). Comparative genomic analysis revealed a rich repertoire of genes associated with cold environmental adaptation and host-microbe interactions. Notably, we identified biosynthetic gene clusters of aryl polyenes and homoserine lactones, alongside genes involved in surface adhesion and nutrient acquisition, suggesting a specialized symbiotic potential within the zooplankton micro-niche. Phenotypically, the strains are characterized as strictly aerobic, with optimal growth at 15–20&#xa0;°C and 3.0% (w/v) sea salts. These findings expand the genomic and ecological understanding of zooplankton-associated bacteria in polar marine ecosystems, and support the proposal of <i>Pseudocolwellia antarctica</i> sp. nov.</p>

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Genomic and phenotypic insights into Pseudocolwellia antarctica sp. nov., a novel psychrotolerant bacterium with symbiotic potential from Antarctic zooplankton

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月3日

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  • Min Kyo Kim,
  • Seung Ju Oh,
  • Bo Min Lee,
  • Jun Lee,
  • Chung Yeon Hwang

摘要

Zooplankton in the Southern Ocean represent unique microhabitats for microbial communities that contribute significantly to polar biogeochemical cycles. In this study, we performed a polyphasic and genomic characterization of two Gram-negative, psychrotolerant bacterial strains, HL-MZ7T and HL-MZ19, isolated from Antarctic zooplankton. Phylogenetic and phylogenomic analyses clearly placed these isolates within the genus Pseudocolwellia, forming a sister clade to Pseudocolwellia agarivorans QM50T. The complete genomes of HL-MZ7T (4.5 Mbp) and HL-MZ19 (4.6 Mbp) exhibited DNA G + C contents of 36.0% and 35.9%, respectively. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values confirmed that both strains represent a novel genomic species, distinct from P. agarivorans QM50T (79.5% ANI and 24.0% dDDH). Comparative genomic analysis revealed a rich repertoire of genes associated with cold environmental adaptation and host-microbe interactions. Notably, we identified biosynthetic gene clusters of aryl polyenes and homoserine lactones, alongside genes involved in surface adhesion and nutrient acquisition, suggesting a specialized symbiotic potential within the zooplankton micro-niche. Phenotypically, the strains are characterized as strictly aerobic, with optimal growth at 15–20 °C and 3.0% (w/v) sea salts. These findings expand the genomic and ecological understanding of zooplankton-associated bacteria in polar marine ecosystems, and support the proposal of Pseudocolwellia antarctica sp. nov.