BACKGROUND

Among the non-tuberculous mycobacteria, Mycobacterium (M.) avium are important pathogens for humans and/or animals. Currently, there are four M. avium subspecies: subsp. hominissuis (Mah), subsp. paratuberculosis (Map), subsp. avium (Maa), and subsp. silvaticum (Mas). While sufficient data is available for the first three mentioned, only few reports exist on the isolation, epidemiology and even less on the genetic equipment of Mas.

RESULTS

Here, Mas was isolated from an Egyptian goose that died of avian tuberculosis. Subspecies identification was based on the presence of IS901 and IS1245 as well as Mycobacterial Interspersed Repetitive Units-Variable Number Tandem Repeat analysis demonstrating Mas specific profile INMV99 profile. During cultural isolation, Mas showed preference for media with mycobactin supplementation but was not limited to mycobactin-containing media. A closed genome sequence was assembled using short- and long-read sequencing technology. The genome sequence consisted of one circular chromosome of 4.84 Mb (GC content 69.3%) and no plasmid. It was highly similar to the only other available Mas sequence (ANI 99.98%, GGDC 99.7%) and eight Maa sequences (ANI ≥99.88%, GGDC ≥98.9%), although all Maa genomes were larger (approx. 5 Mb). In silico prediction of the metabolic pathways and gene content found that all Maa but no Mas should be able to synthetize ergothioneine and the carotenoid neurosporene. The analysis of the mycobactin cluster mbt-1 made it obvious that in Mas two of the eleven mbt genes (mbtB and mbtE) were probably dysfunctional due frameshift-based disruptions.

CONCLUSIONS

The first complete, high quality, closed genome sequence of a Mas isolate closes a knowledge gap. Even if the collection of further genome sequences is considered necessary, the now existing data set already enables a deeper analysis of M. avium. The found differences in the Mas gene content compared to the closest relative Maa seem to be stable and independent of spatial (France, UK, Germany) and temporal (>40 years) differences on their isolation. These data thus call into question the demand for merging the two subspecies Maa and Mas into one, but further genome sequences from other Mas strains are needed to answer this question conclusively.