The scale and evolutionary significance of horizontal gene transfer in the choanoflagellate Monosiga brevicollis

Abstract

BackgroundIt is generally agreed that horizontal gene transfer (HGT) is common in phagotrophic protists. However, the overall scale of HGT and the cumulative impact of acquired genes on the evolution of these organisms remain largely unknown.ResultsChoanoflagellates are phagotrophs and the closest living relatives of animals. In this study, we performed phylogenomic analyses to investigate the scale of HGT and the evolutionary importance of horizontally acquired genes in the choanoflagellate Monosiga brevicollis. Our analyses identified 405 genes that are likely derived from algae and prokaryotes, accounting for approximately 4.4% of the Monosiga nuclear genome. Many of the horizontally acquired genes identified in Monosiga were probably acquired from food sources, rather than by endosymbiotic gene transfer (EGT) from obsolete endosymbionts or plastids. Of 193 genes identified in our analyses with functional information, 84 (43.5%) are involved in carbohydrate or amino acid metabolism, and 45 (23.3%) are transporters and/or involved in response to oxidative, osmotic, antibiotic, or heavy metal stresses. Some identified genes may also participate in biosynthesis of important metabolites such as vitamins C and K12, porphyrins and phospholipids.ConclusionsOur results suggest that HGT is frequent in Monosiga brevicollis and might have contributed substantially to its adaptation and evolution. This finding also highlights the importance of HGT in the genome and organismal evolution of phagotrophic eukaryotes.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-14-729) contains supplementary material, which is available to authorized users.

Stable-isotope probing and metagenomics reveal predation by protozoa drives E. coli removal in slow sand filters

“…The 20 significant protozoan species represented 15 different genera and members from the flagellate, ciliate and amoeboid groups, all of which are known predators of E. coli (Weekers et al, 1993;Fleck et al, 2000;Fey et al, 2007;Cassidy-Hanley, 2012;Yue et al, 2013). Referring to Figure 4c, it can be seen that the proportion of significant protozoan species in 13 C samples increased over time, compared with Figure 2 Absolute numbers of 16S, 18S and E. coli specific 16S rRNA in 12 C and 13 C fractions, determined by qPCR assays.…”

“…The importance, and dominance, of M. brevicollis from the beginning to the end of the experiment is not surprising as it is known to have a critical role in marine global carbon cycling (Yue et al, 2013). Further, its dominance over other protozoan grazers including T. spp.…”

“…Possessing a microvilli collar, which holds bacteria from the water flow and allows them to be engulfed at a later time (Yue et al, 2013), hence providing energy storage for less plentiful times. 2.…”

Bacterial Influences on Animal Origins

“…Yue et al (2013) have calculated that 4.4% of the Monosiga brevicollis genome derives from LGT, one of the highest rates reported for unicellular eukaryotes to date. The phosphofructokinase gene from Monosiga ovata may have originated in spirochetes (Bapteste et al 2003) and pathways for amino acid biosynthesis in M. brevicollis also seem to have been acquired from bacteria (Torruella et al 2009;Sun and Huang 2011).…”

The cell survival pathways of the primordial RNA-DNA complex remain conserved in the extant genomes and may function as proto-oncogenes

“…In addition to vertical inheritance, and to endosymbiotic gene transfer from permanently implanted mitochondria and plastids, choanofl agellates acquired nu merous horizontally trans ferred genes, most of them from algae and prokaryotes (bacteria). Most of these genes remain active in carbo hydrate and amino acid metabolism [27]. The 41.6 Mb genome packs approx.…”