Flavobacterium difficile sp. nov., isolated from a freshwater waterfall

Area of Science:

• Microbiology
• Bacterial Taxonomy
• Environmental Microbiology

Background:

• The genus Flavobacterium comprises diverse Gram-negative bacteria found in various environments.
• Accurate taxonomic classification is crucial for understanding bacterial roles and interactions in ecosystems.
• Isolation and characterization of novel strains contribute to the comprehensive knowledge of microbial biodiversity.

Purpose of the Study:

• To taxonomically characterize a novel bacterial strain, KDG-16 T, isolated from a freshwater environment.
• To determine the phylogenetic position and distinctiveness of strain KDG-16 T within the genus Flavobacterium.
• To propose a new species designation based on polyphasic taxonomic data.

Main Methods:

• Isolation and cultivation of bacterial strain KDG-16 T from a freshwater waterfall in Taiwan.
• Morphological, physiological, and biochemical characterization of the isolate.
• Phylogenetic analysis using 16S rRNA gene sequences and bacterial core genes.
• Genomic analysis including average nucleotide identity (ANI), average amino acid identity (AAI), and digital DNA-DNA hybridization (dDDH).
• Analysis of major fatty acids, polar lipids, polyamines, and isoprenoid quinones.

Main Results:

• Strain KDG-16 T is a Gram-negative, strictly aerobic, motile, rod-shaped bacterium forming light yellow colonies.
• Optimal growth conditions include 20-25 °C, pH 6-7, and 0% NaCl.
• Phylogenetic analyses placed strain KDG-16 T within the genus Flavobacterium, with highest 16S rRNA similarity to *Flavobacterium terrigena* DSM 17934 T (97.7%).
• ANI, AAI, and dDDH values were below species demarcation thresholds, confirming its novelty.
• Key chemotaxonomic features included specific predominant fatty acids, polar lipids, homospermidine as the major polyamine, and MK-6 as the major isoprenoid quinone.
• The G+C content of the genomic DNA was 31.6%.

Conclusions:

• Based on comprehensive polyphasic taxonomic data, strain KDG-16 T represents a novel species within the genus Flavobacterium.
• The proposed name for this new species is *Flavobacterium difficile* sp. nov.
• The type strain is KDG-16 T (= BCRC 81194 T = LMG 31332 T).