Short-Term Physiological and Transcriptomic Analysis of Saxitoxin-Producing and Nonproducing Raphidiopsis raciborskii (Cyanobacteria) under an Extremely High CO2 Environment

Findings about CO2 dynamics in the Earth’s ancestral atmosphere have suggested much higher concentrations in past eras. Along this line, cyanobacteria are an early evolved photosynthetic group that is suggested to have experienced both high and low CO2 availability since their Precambrian origin, and therefore, it is reasonable to assume that these microbes have the potential to cope with these scenarios by rapidly adjusting to various carbon dioxide levels. Thus, in this work, we performed a short-term (72-h) investigation of the physiological parameters (cell growth, photosynthesis and saxitoxin production) of toxic and nontoxic strains of the cyanobacterium Raphidiopsis raciborskii challenged by an extremely high pCO2 (40,000 ppm). Additionally, the transcriptomic profile (regarding the carbon concentrating mechanism and photosynthesis) of selected toxic and nontoxic strains is also presented. We found that short-term exposure to extremely elevated CO2 concentrations did not affect R. raciborskii physiology regardless of toxin production. However, transcripts related to bicarbonate transporters and the RuBisCO enzyme indicated the upregulation of CCM and downregulation of the Calvin cycle, respectively. According to our findings, at least at the initial growth phase, R. raciborskii was able to cope with a very high CO2 level, which shed light on the understanding that this species might have the potential to cope with carbon dioxide in water above the predicted levels

Symbiont modulates expression of specific gene categories in Angomonas deanei

Trypanosomatids are parasites that cause disease in humans, animals, and plants. Most are non-pathogenic and some harbor a symbiotic bacterium. Endosymbiosis is part of the evolutionary process of vital cell functions such as respiration and photosynthesis. Angomonas deanei is an example of a symbiont-containing trypanosomatid. In this paper, we sought to investigate how symbionts influence host cells by characterising and comparing the transcriptomes of the symbiont-containing A. deanei (wild type) and the symbiont-free aposymbiotic strains. The comparison revealed that the presence of the symbiont modulates several differentially expressed genes. Empirical analysis of differential gene expression showed that 216 of the 7625 modulated genes were significantly changed. Finally, gene set enrichment analysis revealed that the largest categories of genes that downregulated in the absence of the symbiont were those involved in oxidation-reduction process, ATP hydrolysis coupled proton transport and glycolysis. In contrast, among the upregulated gene categories were those involved in proteolysis, microtubule-based movement, and cellular metabolic process. Our results provide valuable information for dissecting the mechanism of endosymbiosis in A. deanei