Abstract
The facultative, chemolithotrophic bacteria Hydrogenophilus
thermoluteolus is an understudied thermophilic, hydrogen- and
thiosulfate- oxidizing microorganism that has been found globally in hot
spring environments. It was identified in a series of four soil samples
collected around the Polloquere hot spring of Lauca National Park,
Chile, in 10m intervals from the hot spring water line.
Metagenome-assembled genomes (MAGs) of H. thermoluteolus were
reconstructed from each sample, exhibiting high completion and a 98%
average nucleotide identity with the reference genome of the cultured
H. thermoluteolus isolate. In this study, we collected and
analyzed publicly available genomes of H. thermoluteolus and
other members of the Hydrogenophilceae family derived from
cultures and metagenomes from a diverse set of geothermal environments
for pangenomic comparison with the Polloquere MAGs. The Polloquere soils
are characterized by distinct changes to the environmental chemistry and
biology across the 30m distance from the hot spring. In particular,
increased aridity and pH, as well as lower temperatures and biomass,
coincided with a shift from a characteristic geothermal microbial
population, to that of an arid desert community. Notably, however, the
presence and relative abundance of H. thermoluteolus remained
stable over the same distance (~0.1% of the total
community). Using pangenomics, we were able to deduce several genomic
differences between soil samples closest (0m) and furthest (30m) from
the hot spring, as well as between the Polloquere MAGs and the cultured
reference. Functionally, the 30m MAG lacked carbon fixation
capabilities, while all of the soil MAGs showed added genomic capacity
for denitrification not present in the reference genome. These results
contribute significantly to the pool of genomic data for H.
thermoluteolus, adding to our understanding of the organism’s high
metabolic flexibility. The Polloquere MAGs also represent a rare example
of this organism appearing in a dry, colder, soil environment,
presumably transported from the local hot spring. This study
investigates how the genomes and metabolisms of H. thermoluteolus
vary between environments from a biogeographical perspective, both
globally and across a small spatial distance defined by a steep
environmental gradient.