We report the first description of the microbial community in a stream of acidic hydrothermal waters on volcanically active White Island, New Zealand, using both molecular and microbiological methods. α- and β-Proteobacteria, green-sulfur bacteria, and uncultured Firmicutes were identified from the community DNA-based 16s rRNA gene library. The same bacterial groups and the Rhodophyte Cyanidium caldarium were represented in enrichment cultures. C. caldarium, two Firmicutes and an acidophilic α-Proteobacterium, Acidiphilium cryptum, were brought into pure culture. Bacteria cultured from the stream grow at pH ≥2, and the Cyanidium grows at pH 0.2.