Gluconacetobacter brunescens sp. nov., a Novel Acetic Acid Bacterium Isolated from Pear Vinegar, Producing a Water-Soluble Brown Pigment.

The clade Gluconacetobacter comprises eleven species originating from various sources such as rhizosphere soil, pink sugarcane mealybug, and vinegar. During sampling of organic vinegars, we isolated strain Hr-1-5, which exhibits high 16S rRNA gene sequence identities (≤98.6%) and low 16S-23S rRNA gene internal transcribed spacer (ITS) sequence identities (≤92.1%) with Gluconacetobacter species. Further genome analysis confirmed that strain Hr-1-5 is a distinct species, supported by an average nucleotide identity (ANIb) of ≤90.6% and an in silico DNA-DNA hybridization (dDDH) value of ≤46% compared with other recognized Gluconacetobacter species. Strain Hr-1-5 darkens the growth medium to a deep brown after 4-5 days of submerged cultivation and similarly colors agar medium after 5-6 days. In silico genome analysis suggests that the strain synthesizes pyomelanin. Phenotypically, it is distinguished from its closest Gluconacetobacter relatives by its ability to produce 5-keto-D-gluconic acid, but not 2-keto-D-gluconic acid, and by its capacity to grow on D-ribose, among other traits. These findings support the classification of strain Hr-1-5 as a novel species, for which we propose the name Gluconacetobacter brunescens sp. nov. Hr-1-5T (=ZIM B1168T = LMG 33629T). Strain Hr-1-5 is of biotechnological interest for its pigment production and enables the in situ production of colored cellulose in a co-culture with a cellulose-producing acetic acid bacterium.