NEW CULTURE-BASED AND GENOMIC CHARACTERIZATION OF EXTREMELY ACIDOPHILIC ACIDITHIOBACILLUS SPP. FROM SULFIDIC CAVES

Caves form by sulfuric acid speleogenesis when anoxic fluids bearing hydrogen sulfide (H₂S) encounter air-filled pores or oxygenated groundwater. Substantial cave enlargement occurs above the water table where hydrogen sulfide degasses into the cave atmosphere and oxidizes to sulfuric acid on the moist cave walls. This sulfide gas represents the primary energy source for extreme acidophiles that colonize subaerial surfaces, where they produce pendulous, highly acidic (pH 0-2) “snottite” biofilms and contribute to cave formation by rapidly oxidizing sulfide to sulfuric acid.

Previous research has shown that the numerically dominant microorganisms in these biofilms are members of the genus Acidithiobacillus. However, detailed physiological and genomic studies of these strains have not yet been performed. We evaluated pH tolerance and sulfur utilization capabilities of extremely acidophilic At. thiooxidans from the Frasassi and Acquasanta cave systems in Italy, and show that they can grow from pH values as low as 0.2 to 6. We also evaluated sulfur utilization capabilities through culture-based methods and are relating these capabilities to the genomic properties of the strains. Likewise, snottites from sulfidic caves in Mexico are also dominated by Acidithiobacillus spp., but contain different microbial assemblages (D’Auria et al., 2018). We used single molecule long-read sequencing (Pacific Biosciences) to generate a metagenomic dataset from a snottite sample collected from Cueva de Villa Luz in 2013. Based on this metagenomic evidence, Acidithiobacillus spp. from Cueva de Villa Luz are autotrophs with pathways for inorganic sulfur compound oxidation that include a partial SOX system, heterodisulfide reductase, and multiple sulfide:quinone oxidoreductases. We will also present results on new Acidithiobacillus strains isolated on elemental sulfur media from Cueva de Villa Luz and describe how Acidithiobacillus spp. from this North American cave system differ from snottite-forming At. thiooxidans from the Italian caves.

References:

D'Auria, G., Artacho, A., Rojas, R. A., Bautista, J. S., Méndez, R., Gamboa, M. T., Gamboa, J. R., Gómez-Cruz, R. (2018). Metagenomics of Bacterial Diversity in Villa Luz Caves with Sulfur Water Springs. Genes, 9(1), 55. doi: 10.3390/genes9010055.