Genome sequencing at BU helps solve century old microbial mystery.

The giant phototrophic bacterium Thiospirillum jenense was first discovered in 1838. Its large size (up to 100μm), spiral shape, orange-brown color, and formation of sulfur globules visible under the light microscope, made it an interesting study object for several renowned microbiologists throughout the 20th century.

Thiospirillum jenense

Microscopic image of Thiospirillum jenense.

Although a very intriguing organism, it was proven to be extremely difficult to cultivate in the lab and even to date, no pure culture has been obtained. For a long time, the only source of this bacterium was a pond in former East Germany where it grew April to July, and bacterial cultures had to be smuggled across the then closed borders to West Germany. For more than five decades, the problems in cultivation of Tsp. jenense and later also the missing availability of cultures, have disabled further detailed studies.

Even though the growth and phototactic behavior was studied, nothing was known about the molecular genetics of this intriguing species, not even 16S rRNA sequences, so no complete taxonomic classification could be performed. Up until now.

Illumina-based sequencing was performed at Bellevue University on an enriched sample of Thiospirillum jenense, obtained from Dr. Johannes Imhoff from the GEOMAR Ocean Research Center in Kiel (Germany). Genome sequencing and metagenomic binning analysis now provided the full genome of Thiospirillum jenense which was published just this week in Archives of Microbiology. It showed the unique placement of this species amongst the purple sulfur bacteria and, in addition, potentially resolved some of the genetic reasons behind the challenges of cultivating Tsp. jenense that have been limiting further experiments in the past.

One key component appears to be lack of a high-affinity oxidase (FixNOP), which presumably renders the cells highly sensitive to oxygen damage. In addition, the two sequenced contaminant species, Rhodopseudomonas palustris and a new species Rhodoferax jenense, might help with removal of oxygen in the cultures. These results likely explain the difficulties with obtaining pure cultures of Tsp. jenense as described in the paper, and opens up the doors for new cultivation methods.

Having genomic and genetic data available for Tsp. jenense has widened our understanding of the microbial diversity and will undoubtedly help to further identify similarly unique species in environmental samples, where they play an important role in the sulfur cycle and other nutrient recycling in the environment.

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