Cymbomonas tetramitiformis - a peculiar prasinophyte with a taste for bacteria sheds light on plastid evolution

Abstract

Cymbomonas tetramitiformis is a peculiar green alga that unites in one cell the abilities of photosynthesis and phagocytosis, which makes it a very useful model for the study of the evolution of plastid endosymbiosis. We have pondered over this issue and propose an evolutionary scenario of trophic strategies in eukaryotes, including primary and secondary plastid endosymbioses. C. tetramitiformis is a prototroph, just like the common ancestor of Archaeplastida was, and can synthesize most small organic molecules contrary to other eukaryotic phagotrophs, e.g. some metazoans, amoebozoans, and ciliates, which have not evolved tight endosymbiotic relationships. In order to establish a permanent photosynthetic endosymbiont they do not have to become prototrophs, but have to acquire the genes necessary for plastid retention via horizontal (including endosymbiotic) gene transfer. Such processes occurred successfully in the ancestors of eukaryotes with permanent secondary plastids and thus led to their great diversification. The preservation of phagocytosis in Cymbomonas (and some other prasinophytes as well) seems to result from nutrient deficiency in their oligotrophic habitats. This forces them to supplement their diet with phagocytized prey, in contrasts to the thecate amoeba Paulinella chromatophora, which also successfully transformed cyanobacteria into permanent organelles. Although Paulinella endosymbionts were acquired very recently in comparison to primary plastids, Paulinella has lost the ability to phagocytose, most probably due to the fact that it inhabits nutrient-rich environments, which renders the phagotrophy nonessential.

How Does Salinity Shape Bacterial and Fungal Microbiomes of Alnus glutinosa Roots?

“…Most of the studies on the endophytes were focused on non-woody crops, moreover most of them used culture-dependent methods ( Shen and Fulthorpe, 2015 ; Szymańska et al, 2016 ). Data on bacterial and fungal endophytes in roots of forest trees under saline stress are very limited ( Ju et al, 2014 ; Hrynkiewicz et al, 2015 ; Thiem et al, 2017 ), and our work is the first report describing application of metagenomics to such a community with particular emphasis on root symbionts.…”

“…The study was carried out in mid-northern Poland at two test sites: a non-saline one in Pszczółczyn (53° 00′22.9″ N, 17° 54′57.2″ E; NS) and a saline one in Słonawy (53° 01′26.6″ N, 17° 37′47.3″ E; S) ( Thiem et al, 2017 ). Salinity of soils in this area results from the impact of saline springs contacting with the Zechstein (Permian) salt deposits ( Dadlez and Jaroszewski, 1994 ).…”

Horizontal and endosymbiotic gene transfer in early plastid evolution

“…This transfer was probably accompanied by transfers from bacterial sources (for example Z ahonov a et al, 2018). Unexpectedly, the analysis of nuclear genes of algal origin in eukaryotic lineages Gagat & Mackiewicz (2017) with complex plastids has revealed a wide range of putative algal donors that are different from the algal endosymbionts that exist today as secondary plastids (Curtis et al, 2012). For instance, despite diatoms containing plastids clearly derived from red algae, phylogenetic analysis of diatom nuclear genomes has suggested that > 1700 nucleus-encoded genes were apparently transferred from green algae (Moustafa et al, 2009).…”

Complete Genome Sequence of Bacillus paralicheniformis MDJK30, a Plant Growth-Promoting Rhizobacterium with Antifungal Activity

“…B. paralicheniformis is a Gram-positive species of the Bacillus genus. Rubén Palacio-Rodríguez et al reported that B. paralicheniformis LBEndo1 can promote the growth of Arabidopsis thaliana ( 5 ). B. paralicheniformis MDJK30 was isolated from the rhizosphere of peony in Shandong, China.…”