Sphingomonas sp. DBB INV C78

Tiamulin (TIA) is a commonly used veterinary antibiotic. It is persistent in the animal digestive system and in downstream receiving environments like soil where it ends after manuring. We aimed to isolate TIA-degrading bacteria that could be potentially utilized as bioaugmentation agents for mitigating TIA environmental pressure. A strain able to degrade TIA and use it as sole C source was isolated from a soil exhibiting enhanced biodegradation of the antibiotic. The isolate degraded TIA at concentrations up to 100 ug ml-1, with pH and temperature optima of 6.5-7.5 and 16-25 celcius respectively. Phylogenomic analysis deemed the isolate to be a new Sphingomonas species (83.87 % ANI with S. laterariae, < 95 %), which was named Candidatus Sphingomonas perruchonii. Genomics and transcriptomics revealed the TIA-driven induction of features conducive with the antiotrophic character of Ca. Sphingomonas perruchonii like (i) ABC-F transporters and efflux pumps able to protect the ribosome and microbial cells from TIA, and (ii) oxygenases (e.g. P450 cytochrome) and hydrolases (e.g. alpha/beta-hydrolases and amidohydrolases) possibly contributing to its degradation. LC-MS/MS analysis detected putative transformation products (TPs) of TIA, leading to a proposed transformation pathway. This involved a primary oxidation of the tricyclic moiety of TIA to a mono-hydroxylated derivative (TIA-O), potentially mediated by the highly upregulated monoxygenases, which was either further oxidized to TIA-O2 or hydrolysed, by the upregulated hydrolase or amidohydrolases, to 2-diethylamino-ethyl-thio acetic acid, both not degrading further. Further in vitro functional analysis will verify the role of these genes in the transformation of TIA.