Abstract
Diatoms are heterokont algae derived from a secondary symbiotic event in which a eukaryotic host cell acquired an eukaryotic red alga as plastid. The multiple endosymbiosis and horizontal gene transfer processes provide diatoms unusual opportunities for gene mixing to establish distinctive biosynthetic pathways and metabolic control structures. Diatoms are also known to have significant impact on global ecosystems as one of the most dominant phytoplankton species in the contemporary ocean. As such their metabolism and growth regulating factors have been of particular interest for many years. The publication of the genomic sequences of two independent species of diatoms and the advent of an enhanced experimental toolbox for molecular biological investigations have afforded far greater opportunities than were previously apparent for these species and re-invigorated studies regarding the central carbon metabolism of diatoms. In this review we discuss distinctive features of the central carbon metabolism of diatoms and its response to forthcoming environmental changes and recent advances facilitating the possibility of industrial use of diatoms for oil production. Although the operation and importance of several key pathways of diatom metabolism have already been demonstrated and determined, we will also highlight other potentially important pathways wherein this has yet to be achieved.
Highlights
Diatoms are unicellular, photosynthetic, eukaryotic algae, which are ubiquitous in the world's oceans and freshwater systems
The full set of genes related to carbon metabolism was first suggested on the completion of the T. pseudonana genome [13] whilst a metabolic model was proposed for P. tricornutum based on the whole genome sequence [15]
An increase in abundance of proteins related to the synthesis of acetyl-CoA, which is a precursor for fatty acid biosynthesis, was observed. These results suggest that an increase in fatty acid biosynthesis occurs only at later stages of the response to nitrogen deprivation [20] whilst an increase in the abundance of proteins related to glycolytic and tricarboxylic acid (TCA) cycle enzymes was observed at earlier stages. This observation indicates that the central carbon metabolism response of T. pseudonana to nitrogen starvation might differ considerably from that seen in plants and other eukaryotic photoautotrophic organisms studied to date
Summary
Photosynthetic, eukaryotic algae, which are ubiquitous in the world's oceans and freshwater systems. Diatoms were derived by a secondary endosymbiotic event, which occurred between an unknown eukaryotic cell and a red alga In this process the diatom acquired genes from two eukaryotic genomes. In addition there is an increasing body of evidence, which suggests the occurrence of a considerable level of horizontal gene transfer among marine organisms [10,11] Such an evolutionary background renders algae as a "melting pot" of genes and provides them with a particular opportunity to evolve new gene and metabolic networks [12]. Despite this fact, a large number of diatom proteins are shared by many groups of photosynthetic eukaryotes, namely red alga, green plant and cyanobacterium, and many of them are likely involved in chloroplast functions. We will discuss our current understanding and major knowledge gaps with particular focus on (1) central carbon metabolism, (2) adaptation to environmental conditions and (3) the importance of storage lipids as energy reserves for diatoms and their potential exploitation as a source of biofuel
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