Limnobacter alexandrii sp. nov., a thiosulfate-oxidizing, heterotrophic and EPS-bearing Burkholderiaceae isolated from cultivable phycosphere microbiota of toxic Alexandrium catenella LZT09.

A novel Gram-negative, aerobic, motile and short rod-shaped bacterium with exopolysaccharides production, designated as LZ-4, was isolated from cultivable phycosphere microbiota of harmful algal blooms-causing marine dinoflagellate Alexandrium catenella LZT09 which produces paralytic shellfish poisoning toxins. Strain LZ-4 was able to use thiosulfate (optimum concentration 10 mM) as energy source for bacterial growth. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain LZ-4 belonged to the genus Limnobacter, showing high 16S rRNA gene sequences similarities with L. thiooxidans DSM 13612 (99.4%), L. humi NBRC 11650 (98.2%) and L. litoralis NBRC 105857 (97.2%), respectively. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between LZ-4 and L. thiooxidans DSM 13612 were 78.9 and 21.9%, respectively. Both values were far lower than the thresholds (95-96% for ANI and 70% for dDDH) generally accepted for new species delineation. The respiratory quinone of strain LZ-4 was Q-8. The dominant cellular fatty acids were determined as summed feature 3 (C ω6c/ω7c), summed feature 8 (C ω6c/ω7c) and C. Polar lipids profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminolipids and three unidentified polar lipids. The genomic DNA G+C content of strain LZ-4 was 52.5 mol%. Based on polyphasic characterization, strain LZ-4 represents a novel species of the genus Limnobacter, for which the name Limnobacter alexandrii sp. nov. is proposed. The type strain is LZ-4 (=CCTCC AB 2019004  =KCTC 72281).