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

Abstract

The nature of unusual aquatic microbial formations in flooded passages of cave systems in the Nullarbor region of Australia was investigated using electron microscopy and DNA analysis. The caves are located in a semiarid region but intersect the watertable at depths of approximately 100 m below the surface. Throughout submerged portions of the caves divers have noted the presence 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-shaped cells, and microcrystals of calcite in a mucoid matrix. Molecular phylogenetic analysis of the community structure revealed approximately 12% of clones showed high similarity to autotrophic nitrite-oxidizing bacteria (Nitrospira moscoviensis). The remainder of the clones exhibited a high proportion of phylogenetically novel sequence types. Chemical analysis of water samples 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 structures may represent biochemically novel, chemoautotrophic communities dependent on nitrite oxidation.

Obligate oil-degrading marine bacteria

“…Nr. DQ337077; [28]), hydrocarbon-polluted saline soil ( [29]) and various geothermal areas in Italy and USA (Yellowstone) [30,31] (Figure 2). This ubiquity of A. borkumensis is presumably due to its capacity to grow on many saturated petroleum fraction constituents and on biogenic hydrocarbons: straight-chain and branched alkanes, isoprenoids, and long-side-chain alkyl compounds, including alkylmonocycloalkanes, alkylbenzenes, and organic alkyl-sulfuric compounds [32,33].…”

Life in the dark: metagenomic evidence that a microbial slime community is driven by inorganic nitrogen metabolism

“…Although the surface environment is semiarid, a number of aquatic, subterranean caves extend to considerable distances below the Nullarbor karst, intersecting the water table at a depth of around 100 m below the surface. Exploration of these underwater passages by cave divers has revealed the presence of unusual microbial biofilms, dense 'mantles' or 'curtains' of biological material, known as Nullarbor cave slimes (Holmes et al, 2001). Cave slime communities consist of long, tendril-like structures or amorphous biofilms attached to cave surfaces.…”

“…These microbial formations are observed in areas of complete darkness, deep within submerged regions of the cave systems. They comprise a high standing biomass and can be up to 1 m in length (Holmes et al, 2001). No aquatic macrofauna has been recorded in these regions of the caves (Richards, 1971).…”

“…Indeed, filtered water samples collected from the vicinity of the microbial material were previously shown to contain no detectable organic carbon (James and Rogers, 1994). Chemical analysis of the water samples did show, however, that there are relatively high levels of nitrite as well as significant sulphate and nitrate in many of the caves (Holmes et al, 2001). The composition and metabolism of these communities is therefore of particular interest, with the microorganisms comprising these structures presumably capable of some form of chemolithotrophy.…”

Untitled

“…Hasta la fecha, los estudios que han analizado la colonización bacteriana en cuevas mediante técnicas moleculares, sin cultivos previos son relativamente escasos y no han proporcionado información funcional sobre los microorganismos detectados; por ejemplo, las cuevas de Lechugilla, Spider, Hidden, Ceespool y Fairy en Estados Unidos Engel et al, 2001;Barton et al, 2004); Frasassi Gorge en Italia (Vlasceanu et al, 2000); la Cueva de Villa Luz en Méjico (Hose et al, 2000); el complejo kárstico de Nullarbor en Australia (Holmes et al, 2001). En todos estos casos la diversidad microbiana observada es mucho más variada que la encontrada utilizando sólo cultivos microbianos.…”