Microbial Crusts Research Articles

Biogenic Weathering of Marble Monuments in Didim, Turkey and in Trajan's Column, Rome

The Temple of Apollo in Didim, Turkey, was built in 560-550 B.C. with marble. Mean annual rainfall there is 656 mm. Much of the marble surface is covered by a black crust of microorganisms. Weathering patterns, associated mainly with cyanobacteria, observed there were: 1. Exfoliation with pleurocapsalean cyanobacteria in fissures. 2. Gradual removal, by splashing rain drops, of marble crystals, the coherence of which is reduced as a result of microbial activity. 3. Pits formed by cyanobacteria living in circular patches. The mechanism described in No. 2, leads there to the creation of depressions where the lithobionts are situated. Trajan's column was erected in Rome 112 C.E. Mean annual rainfall there is ca. 700 mm. The column is almost devoid of microbial life at present, but until 1942 had many patches of microbial black crusts. From 1942 to 1948 it was covered by brick walls and sand as a way of protection against war hazards. The light-demanding microorganisms that populated the monument for hundreds of years disappeared after being covered for 6 years and have not returned yet. Pits resembling those in Didim damaged much of the artistic relief on parts of Trajan's column. The most affected parts are those facing south and southeast. These are the directions of the most common incident rainfall in Rome which bring water at high energy to the marble monument.

A modern-type Kimmeridgian reef (Ota Limestone, Portugal): Implications for Jurassic reef models

Upper Jurassic reefs rich in microbial crusts generally appear in deeper (sponge—‘algal’ crust reefs) or in very shallow but protected settings (coral or coral-coralline sponge meadows with ‘algal’ crusts). Upper Jurassic high-energy reefs (coral reefs and coral-stromatoporoid reefs) normally lack major participation of microbial crusts but rather represent huge bioclastic piles with only minor framestone patches preserved.

Carnian (upper triassic) sponge mounds of the Northwestern Sichuan Basin, China: Stratigraphy, facies and paleoecology

Carnian reef mounds with abundant and highly diverse siliceous sponges (Lyssacinosa and “Lithistida”) occur at the northwestern margin of the Sichuan Basin (Anxian and Mianzhu counties), Southern China. Triassic sediments comprise Ladinian to early Norian deposits. Sponge mounds are confined to the Upper Member of the Carnian Hanwang Formation, being late Carnian in age. The mounds correspond to elliptical carbonate bodies with a longer axis up to 100 m and a shorter axis up to 60 m. The dip is 25–30 degrees (but may be accentuated by weathering processes). Mound formation followed a bank phase, represented by the underlying Oolitic Bank Facies and the Bioclastic Bank Facies, both of which were formed in medium to high energy environments. Deepening of the basin, perhaps caused by synsedimentary block-faulting at the shelf-margin, is paralleled by the formation of the sponge mounds. The mound core, proximal and distal mound flanks as well as the intermound sediments differ with regard to frequency, type (colonial, non-colonial, fasciculate etc.) and preservation of siliceous sponges and other biotic elements (especially brachiopods, bivalves, echinoderms). Colonial siliceous sponges dominated during the last mound phase. Termination of mound growth seems to have been caused by the increasing influx of siliciclastic sediment. Triassic siliceous sponge mounds differ from late Jurassic siliceous sponge reefs in the paleogeographical setting, lack of microbial crusts (and rapid synsedimentary cementation), different relief and size of the mounds, and, probably, also in different guild structures.

Desert crust formation and soil stabilization

Abstract A microbially formed soil cover known as desert crust carpets vast regions of land in the arid climates. An accretionary phenomenon in a generally erosional setting, it stabilizes soil and enhances its quality. It is potentially applicable to reclamation of unconsolidated soil in desert regions of the world. This paper reviews the work on microbial crusts, how they develop and contribute to soil quality, and what environmental variables enhance or impede their growth. Microbiological issues relating to the identification, isolation, and culturing of important members of this microbial community are discussed. Some practical problems are considered and suggestions for further research made.

Photofading retardant for epifluorescence microscopy in soil micro-ecological studies

Citifluor, a photofading retardant for epifluorescence studies, was evaluated as a mountant for enhancing algal autofluorescence and Acridine Orange (AO) fluorescence of bacteria and fungi in mineral soils from Antarctic fellfields. It accentuated the colour contrast between red-fluorescing eukaryotic algae, gold-fluorescing cyanobacteria, and green-fluorescing AO-stained bacteria. Photofading was retarded for up to an hour. The technique was applied successfully to microbial enumeration of soil smears, direct examination of intact soil microbial crusts and carborundum paper colonized by meltwater microbes in the field, and for the observation of aerobiological strips from Rotorod samplers. Whilst extending the scope of algal autofluorescence studies, Citifluor made AO technically and economically preferable to FITC, and gave similar bacterial counts.