Obst, M; Dynes, JJ; Lawrence, JR; Swerhone, GDW; Benzerara, K; Karunakaran, C; Kaznatcheev, KV; Tyliszczak, T; Hitchcock, AP: Precipitation of amorphous CaCO3 (aragonite-like) by cyanobacteria: A STXM study of the influence of EPS on the nucleation process, Geochimica et Cosmochimica Acta, 73(14), 4180-4198 (2009), online: 2008-04-24, doi:10.1016/j.gca.2009.04.013 [Link]

An amorphous or nanocrystalline calcium carbonate (ACC) phase with aragonite-like short-range order was found to be a transient precursor phase of calcite precipitation mediated by cyanobacteria of the strain Synechococcus leopoliensis PCC 7942. Using scanning transmission X-ray microscopy (STXM), different Ca-species such as calcite, aragonite-like CaCO3, and Ca adsorbed on extracellular polymers were discriminated and mapped, together with various organic compounds, at the 30 nm-scale. The nucleation of the amorphous aragonite-like CaCO3 was found to take place within the tightly bound extracellular polymeric substances (EPS) produced by the cyanobacteria very close to the cell wall. The aragonite-like CaCO3 is a type of ACC since it did not show either X-ray or electron diffraction peaks. The amount of aragonite-like CaCO3precipitated in the EPS was dependent on the nutrient supply during bacterial growth. Higher nutrient concentrations (both N and P) during the cultivation of the cyanobacteria resulted in higher amounts of precipitation of the aragonite-like CaCO3, whereas the amount of Ca2+ adsorbed per volume of EPS was almost independent of the nutrient level. After the onset of the precipitation of the thermodynamically stable calcite and loss of supersaturation the aragonite-like CaCO3 dissolved whereas Ca2+ remained sorbed to the EPS albeit at lower concentrations. Based on these observations a model describing the temporal and spatial evolution of calcite nucleation on the surface of S. leopoliensis was developed. In another set of STXM experiments the amount of aragonite-like CaCO3 precipitated on the cell surface was found to depend on the culture growth phase: cells in the exponential growth phase adsorbed large amounts of Ca within the EPS and mediated nucleation of ACC, while cells at the stationary/death phase neither adsorbed large amounts of Ca2+ nor mediated the formation of aragonite-like CaCO3. It is suggested that precipitation of an X-ray amorphous CaCO3 layer by cyanobacteria could serve as a protection mechanism against uncontrolled precipitation of a thermodynamically stable phase calcite on their surface.

Upcoming ...

BayCEER Colloquium:
Th. 2021-01-14
Mineral surfaces and organic matter accrual in soils
Th. 2021-01-21
The impact of trees on soil organic carbon dynamics in the Subarctic - Priming effects and microbial N mining
Ecological-Botanical Garden:
Su. 2020-12-06
Entfällt: Führung nach Anmeldung: Zimt & Mandelkern: Pflanzen in der Weihnachtsbäckerei
Su. 2021-01-03
Führung nach Anmeldung: Mit kühlem Kopf ins Neue: Winterspaziergang
Geographisches Kolloquium:
Tu. 2020-12-08
People, pathogens, places: where medical geography meets disease ecology?
BayCEER Blog
Why Science Communication?
Stoichiometric controls of C and N cycling
Flying halfway across the globe to dig in the dirt – a research stay in Bloomington, USA
Picky carnivorous plants?
RSS Blog as RSS Feed
Weather research site
Luftdruck (356m): 948.8 hPa
Lufttemperatur: 2.4 °C
Niederschlag: 0.0 mm/24h
Sonnenschein: <1 h/d
Wind (Höhe 17m): 10.8 km/h
Wind (Max.): 25.9 km/h
Windrichtung: SO

Globalstrahlung: -2 W/m²
Lufttemperatur: -2.4 °C
Niederschlag: 0.0 mm/24h
Sonnenschein: <1 h/d
Wind (Höhe 32m): 0.0 km/h

This site makes use of cookies More information