The microbial ecology of some Italian hot-spring travertines

The microbial flora of eight Italian travertine-depositing hot springs is described. At all sites, the flora was dominated by photosynthetic microbes forming two well-defined communities. At temperatures of 10-40 o C and sulphide levels of 50-500 μM/l a community of the non-filamentous sulphur bacteria Chlorobium chlorovibrioides, Chromatium minus and Thiobacillus spp. predominated. At 40-60 o C and sulphide levels of 0-100 μM/l, a community of the filamentous photosynthetic bacteria Chloroflexus sp., Lyngbya (Phormidium) laminosum and Spirulina labyrinthiformis occurred. Other bacteria isolated included Desulphovibrio cf. thermophilus, Thiosphaera sp. and Oscillatoria. The communities have not previously been recognized in European thermal waters. None of the bacteria was restricted to travertine-depositing waters but Spirulina has been widely reported from warm, calcium-rich sites. The distribution of these bacteria was influenced most by sulphide and temperature. Although some travertine fabrics were clearly modified by the presence of bacteria, a direct influence of bacterial metabolism on travertine formation remains to be established at these sites. Measurements of temperature, pH, E h , dissolved oxygen, carbon dioxide, Ca, Mg, Na and sulphate are provided