Phenylobacterium ferrooxidans sp. nov., Isolated From A Sub-surface Geothermal Aquifer In Iceland

A novel bacterial strain, HK31-GT, was isolated from a subsurface geothermal aquifer (Hellisheidi, SW-Iceland) and was characterized using a polyphasic taxonomic approach. Phylogenetic analysis of 16S rRNA gene along with phylogenomic position indicated that the novel strain belongs to the genus Phenylobacterium.

Cells are motile Gram-negative thin rods. Physiological characterization showed that strain HK31-GT is a mesophilic bacterium able to grow from 10 to 30°C, at pH values between 6 and 8 and at NaCl concentrations between 0 and 0.5 %.

Optimal growth was observed without sodium chloride at 25°C and pH 6. Strain HK31-GT is chemoorganoheterotroph and its major saturated fatty acids are C18:1ω7c, C16:1ω6c and C16:0, the predominant quinone is Q-10 and the major polar lipid is phosphatidylglycerol.

The new strain also possesses the capacity to use ferrous iron (Fe(II)) as the sole energy source and can also be considered as a chemolithoautotrophic microorganism. The overall genome of strain HK31-GT was estimated to be 4.46 Mbp in size with a DNA G + C content of 67.95 %. Genes involved in iron metabolism were identified, but no genes typically involved in Fe(II)-oxidation were found.

According to the overall genome relatedness indices (OGRI) values, six MAGs from groundwater have been assigned to the same species as the new strain HK31-GT. Furthermore, OGRI values between the genome of strain HK31-GT and the genomes of its closest relatives are below the species delineation threshold.

Therefore, given the polyphasic approach used, strain HK31-GT represents a novel species of the genus Phenylobacterium, for which the name Phenylobacterium ferrooxidans sp. nov. is proposed. The type strain is HK31-GT (DSM 116432T = UBOCC-M-3429T = LMG 33376T).

Transmission electron microscopy microphotographs of cells of strain HK31-GT grown on R2A at 25 °C for 3 days. (a) Some cells harbor a cellular appendage, so-called prostheca or stalk (indicated by black arrow). (b) Intracellular granules. (c) A cell with its polar flagellum. (d) Enlargement of image (c). — Systematic and Applied Microbiology

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