Freshwater environments serve as crucial habitats for diverse microorganisms, playing essential roles alongside plants and animals within the ecosystem. Bacteria in these environments are particularly important for maintaining ecosystem functions. Among them, members of the phylum Pseudomonadota are known to be involved in processes such as nitrogen fixation, ammonia oxidation, and biofilm formation. Pseudomonadota comprises six classes: Acidithiobacillia, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Hydrogenophilia, and Zetaproteobacteria. This study reports 43 previously unrecorded species belonging to the phylum Pseudomonadota. They were isolated from various freshwater habitats in Republic of Korea. These strains were isolated and cultured using nine different standard media, with classification based on Gram staining, cell morphology, and biochemical characteristics. Species identity was determined using 16S rRNA gene sequencing, with a similarity threshold of 98.7% for designation as unreported species. Phylogenetic analysis revealed that these 43 strains were distributed across three classes, 13 orders, 28 families, and 39 genera. This research emphasizes microbial diversity in freshwater ecosystems and provides valuable insights into ecological roles and potential novel functions of unreported bacterial species in Korea.

As part of the 2024 research initiative, “Investigation and Discovery of Prokaryotes in Freshwater Systems,” samples were collected from diverse freshwater habitats, including both water and soil environments. Approximately 2,000 bacterial strains were isolated as single colonies and identified through 16S rRNA gene sequence analysis. Among these, 38 strains shared ≥98.7% 16S rRNA gene sequence similarities with those of known bacterial species not previously reported in Korea. These strains were thus categorized as newly recorded bacterial species in Korea. These 38 bacterial strains displayed significant phylogenetic diversities, spanning 2 phyla, 4 classes, 15 orders, 24 families, and 34 genera. These unrecorded species were classified into the following classes: Actinomycetia (with genera including Microcella, Conyzicola, Curtobacterium, Leucobacter, Microbacterium, Frigoribacterium, Lysinibacter, Streptomyces, Nonomuraea, Actinocorallia, Ruania, and Actinoplanes), Alphaproteobacteria (Paracoccus, Youngimonas, Loktanella, Corticibacterium, Neorhizobium, Onobrychidicola, Ferranicluibacter, Aureimonas, Asticcacaulis, and Novosphingobium), Betaproteobacteria (Rhodoferax, Rugamonas, and Cupriavidus), and Gammaproteobacteria (Rheinheimera, Shewanella, Kosakonia, Leclercia, Hafnia, Yersinia, Pseudomonas, Lysobacter, and Acinetobacter ). Further characterization included assessment of Gram reaction, colony and cell morphology, biochemical properties, and phylogenetic relationships. This report presents detailed phylogenetic and phenotypic characteristics of these bacterial species.

As part of the research program “Freshwater Prokaryotic Organisms Research and Discovery,” freshwater samples were collected from the Nakdonggang River. After plating the samples on several culture media and incubating aerobically, approximately 900 bacterial strains were isolated and identified using 16S rRNA gene sequences. Among the bacterial isolates showing higher than 98.7% 16S rRNA gene sequence similarity with those of already confirmed bacterial species previously unreported in Korea, 29 strains were selected. These strains were phylogenetically diverse and belonged to 3 phyla, 6 classes, 13 orders, and 21 genera. At the genus level, these previously unreported species were found to be affiliated with Novosphingobium, Sphingomonas, Polymorphobacter, Croceibacterium, Devosia, Endobacterium, Agaricicola, Bradyrhizobium, Paracoccus, and Pseudotabrizicola of the class Alphaproteobacteria; Undibacterium, Azonexus, and Dechloromonas of the class Betaproteobacteria; Acinetobacter and Budvicia of the class Gammaproteobacteria; Streptomyces, Nocardioides, Mycobacterium, and Cellulomonas of the phylum Actinomycetota; Flavobacterium and Pedobacter of the phylum Bacteroidota. These species were further characterized by examining their Gram reaction, colony and cell morphologies, biochemical properties, and phylogenetic positions. Detailed descriptions of these 29 previously unreported species are provided.

This study investigated unrecorded freshwater bacterial species in Korea. Water and sediment samples were collected from the Nakdong River basin from 2020-2022. Bacterial isolates obtained through the conventional culture method with commercial media were subjected to 16S rRNA gene sequencing to identify unrecorded bacterial species. Results of 16S rRNA gene sequencing of the bacterial isolates revealed that a total of 44 bacterial isolates shared 16S rRNA gene sequence similarities of more than 98.65%, with validly published bacterial species not reported in Korea yet. These isolates were phylogenetically assigned to 4 phyla, 7 classes, 21 orders, 33 families, and 42 genera. A total of 2, 6, 12, and 24 species belonged to phyla Bacillota, Bacteroidota, Actinomycetota, and Pseudomonadota, respectively. Here, we provide details of these 44 unrecorded bacterial species, including Gram staining, colony and cellular morphologies, biochemical properties, and phylogenetic position.

Nine fish and one clam species were collected from freshwater environments in Korea, including four lakes, two streams, and the Nakdong River, to investigate the host-associated bacteria. Hundreds of bacterial strains were isolated from the samples using a cell sorter and a dilution plating method. After identification of the bacterial strains using 16S rRNA gene sequences, 42 strains with greater than 98.7% sequence similarity with validly published species were determined to be unrecorded bacterial species in Korea. These strains were phylogenetically diverse and assigned to four phyla, six classes, 17 orders, 27 families, and 32 genera. At the genus level, the unrecorded species were classified as Corynebacterium, Mycobacterium, Mycolicibacterium, Gordonia, Williamsia, Modestobacter, Brachybacterium, Sanquibacter, Arthrobacter, and Mycolicibacterium of the class Actinobacteria; Empedobacter, and Flavobacterium of the class Flavobacteriia; Fictibacillus, Psychrobacillus, Cohnella, Paenibacillus, Rummeliibacillus, Enterococcus, and Vagococcus of the class Bacilli; Aquamicrobium, Paracoccus, and Sphingomonas of the class Alphaproteobacteria; Achromobacter, Delftia, and Deefgea of the class Betaproteobacteria; and Aeromonas, Providencia, Yersinia, Marinomonas, Acinetobacter, and Pseudomonas of the class Gammaproteobacteria. The 42 unrecorded species were subjected to further taxonomic characterization using gram staining, cellular and colony morphological determination, biochemical analyses, and phylogenetic analyses. This paper provides detailed descriptions of the 42 previously unrecorded bacterial species.