Sphingomonas was defined in 1990 as a group of Gram-negative, rod-shaped, chemoheterotrophic, strictly aerobic bacteria. They possess ubiquinone 10 as their major respiratory quinone, contain glycosphingolipids (GSLs), specifically ceramide, instead of lipopolysaccharide (LPS) in their cell envelopes, and typically produce yellow-pigmented colonies. The GSL serves to protect the bacteria from antibacterial substances. Unlike most Gram-negative bacteria, Sphingomonas cannot carry endotoxins due to the lack of lipopolysaccharides, and has a hydrophobic surface characterized by the short nature of the GSL's carbohydrate portion.[2]
By 2001, the genus included more than 20 species that were quite diverse in terms of their phylogenetic, ecological, and physiological properties. As a result, Sphingomonas was subdivided into different genera: Sphingomonas, Sphingobium, Novosphingobium, Sphingosinicella, and Sphingopyxis. These genera are commonly referred to collectively as sphingomonads. Distinct from other sphingomonads, Sphingomonas genomic structure includes a unique lipid formation, major 2-OH fatty acids, homospermidine as the primary polyamine, and signature nucleotide bases within the 16S rRNA gene. The bacteria holds 3914 proteins, 70 organizational RNA, and 3,948,000 base pairs (incomplete observation).[2]