Multiphase Biomineralization: Enigmatic Invasive Siliceous Diatoms Produce Crystalline Calcite

Abstract

Diatoms are considered unicellular eukaryotic organisms exclusively depositing biogenic silica. Heretofore there has been no report of calcifi cation by these algae. Here it is shown that calcium carbonate within the stalks of Didymosphenia geminata , a nuisance species that has prolifi cally colonized streams and rivers globally, is biogenic in origin and occurs as a network of calcite nanofi bers. The nanofi brous framework in the mineralized polysaccharide matrix imparts mechanical support to the stalks, providing stability in variable fl ow conditions. The results demonstrate that D. geminata possesses cellular and periplasmic carbonic-anhydrases that contribute to carbon fi xation and biomineralization, respectively. The activity of external carbonic-anhydrase was more than 50% of the total activity, which points to its role in anchoring this bioeroding diatom on hard surfaces. The fi rst evidence of multiphase biomineralization by diatoms that deposit both biogenic silica and crystalline biogenic calcite which are imparting distinct functional advantage to the organism is provided.

Adhesive Stalks of DiatomDidymosphenia geminataas a Novel Biological Adsorbent for Hazardous Metals Removal

“…It is apparent from this table that the purified material demonstrated significantly better sorption capacity for lead(II), nickel(II), and cadmium(II) ions in comparison with polysaccharides and lignocellulosic materials. High sorption capacity can be related to the presence of sulfur containing functional groups (−SO 3 H) on the surface of stalks isolated from D. geminata which show better affinity for the metal ions than the hydroxyl and amine groups of chitosan and other polysaccharides.…”

“…The material was then sonicated for 15 min using an ultrasound bath with a power of 95 W and a frequency of 50 Hz (Elmasonic, Germany). After this procedure, the stalks remained in the filter bags, however, the cells were filtered through the filter net . The separated stalks were dried at 105°C for 24 h and then used for adsorption experiments.…”

“…The major monosaccharides are galactose, xylose, and mannose; with predominant glycosyl linkages at 3,4‐Gal, 4,6‐Man, and 4/5‐Xyl. Due to their unique microcapillary capacity stalks of D. geminata serve as reservoirs for ions and small molecules; and help to elevate the diatom above the substratum to provide greater access to light as well as a strong anchor . Therefore, this micro algae is able to cover up to 100% of a substrate with thicknesses >20 cm, greatly altering the physical and biological conditions within streams .…”

Recent biomedical applications of bio-sourced materials

“…For example, unicellular organisms such as magnetotactic bacteria produce magnetite nanoparticles and [102] diatoms produce synthetic siliceous materials [103]. Gadd et al studied the effects of the ureolytic fungi Neurospora crassa, Pestalotiopsis sp.…”

“…Many organisms provide inorganic materials intracellularly or extracellularly [102][103][104]. For example, unicellular organisms such as magnetotactic bacteria produce magnetite nanoparticles and [102] diatoms produce synthetic siliceous materials [103].…”