Revisiting the thermophilic bacterial genus Venenivibrio; physiological, phenotypic, and genotypic (re)characterisation the type strain and novel Venenivibrio isolates.

Abstract

Venenivibrio is a genus of Bacteria that has currently only been detected in Aotearoa New Zealand geothermal hot springs. A single cultivated and characterised isolate, Venenivibrio stagnispumantis CP.B2T, is the sole representative of the genus since its discovery in 2008. In recent years, a molecular survey (1000 Springs Project) of hot springs within the Taupō Volcanic Zone (New Zealand North Island) found that members of Venenivibrio was the most prevalent and abundant genus in the hot springs, which was surprising given the lack of knowledge surrounding the genus. Interrogation of global genetic databases have yet to return any results showing the presence of Venenivibrio outside of New Zealand, indicating that it may be endemic. The goals of this research is to gain a greater understanding of the single known species through characterisation experiments, and to attempt to isolate new strains and/or species from springs that have shown high abundance of Venenivibrio. This will allow for a greater understanding of this unique bacterial genus, its diversity and phenotype.

Springs which demonstrated high abundances of Venenivibrio were targeted and sampled. These samples were then inoculated into an enrichment medium specifically designed to target the hydrogen oxidising, oxygen reducing phenotype of Venenivibrio, with a pH of 5.5 to exclude closely related genera. After multiple dilution series to achieve an axenic culture, seven novel isolates were cultivated, six of which belong to Venenivibrio.

Characterisation experiments were carried out on the type strain, V. stagnispumantis CP.B2T, as well as three of the novel isolates to gain a greater understanding of the genus and its growth ranges. This included NaCl tolerance, oxygen tolerance, anaerobic growth determination, pH range, and temperature range.

Two whole genomes, V. stagnispumantis CP.B2T and Venenivibrio sp. KUI1, were sequenced for whole genome sequencing and comparison, as well as to confirm observations seen in the laboratory. Despite having very similar average nucleotide identities and 16S rRNA gene sequences, they differ significantly in regards to metabolism. Venenivibrio sp. KUI1 contains the mechanisms to reduce sulphur and nitrate, which is not seen in the type strain genome.

Further work will be done in the future to investigate the true and full diversity of the Venenivibrio genus.