Poseidonibacter parvus sp. nov., isolated from a squid

Area of Science:

• Marine Microbiology
• Bacterial Taxonomy
• Genomics

Background:

• Marine environments harbor diverse microbial life, including bacteria associated with marine invertebrates.
• Accurate taxonomic classification of newly isolated bacteria is crucial for understanding microbial diversity and ecological roles.
• The genus *Poseidonibacter* comprises marine bacteria with incompletely defined species boundaries.

Purpose of the Study:

• To characterize a novel bacterium, strain LPB0137^T, isolated from a squid.
• To determine the phylogenetic and genomic relationship of strain LPB0137^T to known *Poseidonibacter* species.
• To formally propose a new species within the genus *Poseidonibacter* based on comprehensive analyses.

Main Methods:

• Isolation and cultivation of strain LPB0137^T on marine agar with 2,3,5-triphenyl tetrazolium chloride (TTC).
• Phenotypic characterization including Gram staining, motility, and colony color.
• Genomic analysis involving chromosome size, DNA G+C content, gene count, rRNA operons, 16S rRNA gene sequencing, average nucleotide identity (ANI), and in silico DNA-DNA hybridization (dDDH).

Main Results:

• Strain LPB0137^T is a Gram-negative, aerobic, short rod-shaped, motile, brownish bacterium.
• Phylogenetic analysis showed 98.3% 16S rRNA gene sequence similarity to *Poseidonibacter antarcticus* SM1702^T.
• Low ANI (83.9%) and dDDH (28.1%) values, along with distinct enzymatic characteristics, distinguished strain LPB0137^T from related species, supporting its novelty.

Conclusions:

• Strain LPB0137^T represents a new species within the genus *Poseidonibacter*, named *Poseidonibacter parvus* sp. nov.
• The type strain for this novel species is LPB0137^T (=KACC 18888^T=JCM 31548^T).
• This finding contributes to the taxonomic understanding of the genus *Poseidonibacter* and marine bacterial diversity.