Biology Reference
In-Depth Information
Another conspicuous feature of diatoms is their production of extracellular
polymeric substances (EPS), a key survival strategy that provides energy
production, habitat stabilization, colony formation, mechanical protection,
adhesion and motility. 1 EPS mainly consists of complex carbohydrates and
glycoproteins and can be secreted externally to form various structures just
as elaborate as the silica cell wall. Some EPS forms are intimately associated
with the frustule as coatings, whereas others such as strands, tethers, pads
and stalks serve primarily as adhesive structures ( Fig. 19.1c ) . 1 The diversity
of EPS structure and function underpins their ability in seeking out nutrient-
rich and suitable photosynthetic conditions and subsequent colonization of
most of the world's aquatic habitats. Their ecological success is epitomized
by diatoms accounting for an estimated 40% of marine primary productivity,
20% of the total photosynthetic CO 2 ixation as well as being predominant
contributors to silicon cycling in oceans. 6 As a major group of organisms
controlling the world's CO 2 levels, the importance of diatoms on future trends
of climate change is well stated. 7
19.2 CURRENT TRENDS IN DIATOM RESEARCH: INFLUENCES
FROM NANOTECHNOLOGY
Diatom research in recent years has seen a signiicant shift in the motivation
behind fundamental aspects of their biology. An emphasis on nanotechnology
research and related applications has certainly been a major factor in shaping
the context of the research. Perhaps the biggest revolution in recent times has
undoubtedly been in research on understanding the formation of the silica
frustule. During this process, the cells convert the soluble form of silicic acid
in the aqueous environment into solid silica. The phenomenon that follows
involves the nanostructuring and moulding of the silica in synchrony with
self-assembly processes to form a new valve for each daughter cell during
replication. Several proposed models provide an overview of the process, 4
though critical aspects still remain a mystery. Diatoms undergo rapid
logarithmic growth rates (>10 6 cells in 3-5 days), thus formation of the valves
occurs at unprecedented speeds, densities and under ambient conditions. It is
no wonder that this process, usually referred to as “diatom biomineralization
and morphogenesis”, has been gripped by the current nanotechnology
wave and grabbed the attention of nanotechnologists and multidisciplinary
researchers alike. It is also the case that numerous recent reviews have
used diatom cell wall formation as a case study for the three-dimensional
(3-D) self-assembly of nanostructures, 8-10 making them synonymous with
nanotechnology practices.
 
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