<P> Diatom genomics brought much information about the extent and dynamics of the endosymbiotic gene transfer (EGT) process . Comparison of the T. pseudonana proteins with homologs in other organisms suggested that hundreds have their closest homologs in the Plantae lineage . EGT towards diatom genomes can be illustrated by the fact that the T. pseudonana genome encodes six proteins which are most closely related to genes encoded by the Guillardia theta (cryptomonad) nucleomorph genome . Four of these genes are also found in red algal plastid genomes, thus demonstrating successive EGT from red algal plastid to red algal nucleus (nucleomorph) to heterokont host nucleus . More recent phylogenomic analyses of diatom proteomes provided evidence for a prasinophyte - like endosymbiont in the common ancestor of chromalveolates as supported by the fact the 70% of diatom genes of Plantae origin are of green lineage provenance and that such genes are also found in the genome of other stramenopiles . Therefore, it was proposed that chromalveolates are the product of serial secondary endosymbiosis first with a green algae, followed by a second one with a red algae that conserved the genomic footprints of the previous but displaced the green plastid . However, phylogenomic analyses of diatom proteomes and chromalveolate evolutionary history will likely take advantage of complementary genomic data from under - sequenced lineages such as red algae . </P> <P> In addition to EGT, horizontal gene transfer (HGT) can occur independently of an endosymbiotic event . The publication of the P. tricornutum genome reported that at least 587 P. tricornutum genes appear to be most closely related to bacterial genes, accounting for more than 5% of the P. tricornutum proteome . About half of these are also found in the T. pseudonana genome, attesting their ancient incorporation in the diatom lineage . </P> <P> Diatoms are a widespread group and can be found in the oceans, in fresh water, in soils, and on damp surfaces . They are one of the dominant components of phytoplankton in nutrient - rich coastal waters and during oceanic spring blooms, since they can divide more rapidly than other groups of phytoplankton . Most live pelagically in open water, although some live as surface films at the water - sediment interface (benthic), or even under damp atmospheric conditions . They are especially important in oceans, where they contribute an estimated 45% of the total oceanic primary production of organic material . Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically . </P> <P> Planktonic diatoms in freshwater and marine environments typically exhibit a "boom and bust" (or "bloom and bust") lifestyle . When conditions in the upper mixed layer (nutrients and light) are favourable (as at the spring), their competitive edge and rapid growth rate enables them to dominate phytoplankton communities ("boom" or "bloom"). As such they are often classed as opportunistic r - strategists (i.e. those organisms whose ecology is defined by a high growth rate, r). </P>

Sediments produced by plants and animals in the sea called