ARCHAEAL AND BACTERIAL DIVERSITY IN ACIDIC TO CIRCUMNEUTRAL HOT SPRINGS IN THE PHILIPPINES

The microbial diversity was investigated in sediments of six acidic to circumneutral

hot springs (Temperature: 60–92 °C, pH 3.72–6.58) in the Philippines

using an integrated approach that included geochemistry and 16S rRNA gene

pyrosequencing. Both bacterial and archaeal abundances were lower in high-temperature

springs than in moderate-temperature ones. Overall, the archaeal

community consisted of sequence reads that exhibited a high similarity (nucleotide

identity > 92%) to phyla Crenarchaeota, Euryarchaeota, and unclassified

Archaea. The bacterial community was composed of sequence reads moderately

related (nucleotide identity > 90%) to 17 phyla, with Aquificae and Firmicutes

being dominant. These phylogenetic groups were correlated with environmental

conditions such as temperature, dissolved sulfate and calcium concentrations in

spring water, and sediment properties including total nitrogen, pyrite, and elemental

sulfur. Based on the phylogenetic inference, sulfur metabolisms appear

to be key physiological functions in these hot springs. Sulfobacillus (within phylum

Firmicutes) along with members within Sulfolobales were abundant in two

high-temperature springs (> 76 °C), and they were hypothesized to play an

important role in regulating the sulfur cycling under high-temperature conditions.

The results of this study improve our understanding of microbial diversity

and community composition in acidic to circumneutral terrestrial hot springs

and their relationships with geochemical conditions.