Phylogenetic structure of unusual aquatic microbial formations in Nullarbor caves, Australia

The nature of unusual aquatic microbial formations in flooded passages of c ave systems in the Nullarbor region of Australia was investigated using ele ctron microscopy and DNA analysis. The caves are located in a semiarid regi on but intersect the watertable at depths of approximately 100 m below the surface. Throughout submerged portions of the caves divers have noted the p resence of unusual microbial formations, These 'microbial mantles' comprise sheets or tongues of mucoid material in which small crystals are embedded, Examination of the biomass revealed it to be primarily composed of densely packed, unbranched filaments, together with spherical-, rod- and spiral-sh aped cells, and microcrystals of calcite in a mucoid matrix. Molecular phyl ogenetic analysis of the community structure revealed similar to 12% of clo nes showed high similarity to autotrophic nitrite-oxidizing bacteria (Nitro spira moscoviensis), The remainder of the clones exhibited a high proportio n of phylogenetically novel sequence types. Chemical analysis of water samp les revealed high levels of sulphate and nitrate together with significant nitrite, The community structure, the presence of nitrite in the water, and the apparent absence of aquatic macrofauna, suggest these microbial struct ures may represent biochemically novel, chemoautotrophic communities depend ent on nitrite oxidation.