Parafrigoribacterium soli sp. nov. and Parafrigoribacterium humi sp. nov., two novel siderophore-synthesizing species isolated from black soil.

Two siderophore-synthesizing species SYSU BS000078 and SYSU BS000231 were isolated from the black soil collected from fields located in Heilongjiang province, China. The results of phylogenetic analysis based on the 16S rRNA gene sequences indicated that these two strains showed the highest sequence similarity to Parafrigoribacterium mesophilum KCTC 19311 (98.61 % and 98.68 %, respectively). The average nucleotide identity (ANI) values between the two strains and other members of the genus Parafrigoribacterium were lower than 95 %, recommended for distinguishing novel prokaryotic species. Cells of strains SYSU BS000078 and SYSU BS000231 were aerobic, motile, Gram-stain-positive and non-spore-forming rods. The colonies of these two strains exhibited a cream pigment, with tidy edges and smooth surfaces. Growth was observed within the temperature range of 4-37 °C (optimal growth at 28 °C) and pH range of 6.0-8.0 (optimal growth at pH 7.0). The predominant polar lipids detected in these two strains included diphosphatidylglycerol and phosphatidylglycerol. The predominant respiratory quinones was MK-9. The major cellular fatty acids (>10 %) were iso-C, anteiso-C, and anteiso-C. The genome size and G + C content of strain SYSU BS000078 were determined to be 2.89 Mbp and 66.5 %, respectively. Meanwhile, SYSU BS000231 exhibited a genome size of 2.81 Mbp, accompanied by a G + C content of 65.8 %. Based on the phenotypic, physiological, genotypic, and phylogenetic data, these two strains represent two novel species of the genus Parafrigoribacterium, which are proposed as Parafrigoribacterium soli sp. nov. SYSU BS000078 (=GDMCC 1.4599 = KCTC 59245), and Parafrigoribacterium humi sp. nov. SYSU BS000231 (=GDMCC 1.3816 = KCTC 59001).