Light dependency of resistance to ionizing radiation in Euglena gracilis

The Influence of Phenol on the Growth, Morphology and Cell Division of Euglena gracilis

Phenol, a monocyclic aromatic hydrocarbon with various commercial uses, is a major pollutant in industrial wastewater. Euglena gracilis is a unicellular freshwater flagellate possessing secondary chloroplasts of green algal origin. This protist has been widely used for monitoring the biological effect of various inorganic and organic environmental pollutants, including aromatic hydrocarbons. In this study, we evaluate the influence of different phenol concentrations (3.39 mM, 3.81 mM, 4.23 mM, 4.65 mM, 5.07 mM, 5.49 mM and 5.91 mM) on the growth, morphology and cell division of E. gracilis. The cell count continually decreases (p < 0.05-0.001) over time with increasing phenol concentration. While phenol treatment does not induce bleaching (permanent loss of photosynthesis), the morphological changes caused by phenol include the formation of spherical (p < 0.01-0.001), hypertrophied (p < 0.05) and monster cells (p < 0.01) and lipofuscin bodies. Phenol also induces an atypical form of cell division of E. gracilis, simultaneously producing more than 2 (3-12) viable cells from a single cell. Such atypically dividing cells have a symmetric "star"-like shape. The percentage of atypically dividing cells increases (p < 0.05) with increasing phenol concentration. Our findings suggest that E. gracilis can be used as bioindicator of phenol contamination in freshwater habitats and wastewater.

Chronic Ionizing Radiation of Plants: An Evolutionary Factor from Direct Damage to Non-Target Effects

In present times, the levels of ionizing radiation (IR) on the surface of Earth are relatively low, posing no high challenges for the survival of contemporary life forms. IR derives from natural sources and naturally occurring radioactive materials (NORM), the nuclear industry, medical applications, and as a result of radiation disasters or nuclear tests. In the current review, we discuss modern sources of radioactivity, its direct and indirect effects on different plant species, and the scope of the radiation protection of plants. We present an overview of the molecular mechanisms of radiation responses in plants, which leads to a tempting conjecture of the evolutionary role of IR as a limiting factor for land colonization and plant diversification rates. The hypothesis-driven analysis of available plant genomic data suggests an overall DNA repair gene families' depletion in land plants compared to ancestral groups, which overlaps with a decrease in levels of radiation exposure on the surface of Earth millions of years ago. The potential contribution of chronic IR as an evolutionary factor in combination with other environmental factors is discussed.

Bioproducts From Euglena gracilis: Synthesis and Applications

In recent years, the versatile phototrophic protist Euglena gracilis has emerged as an interesting candidate for application-driven research and commercialisation, as it is an excellent source of dietary protein, pro(vitamins), lipids, and the β-1,3-glucan paramylon only found in euglenoids. From these, paramylon is already marketed as an immunostimulatory agent in nutraceuticals. Bioproducts from E. gracilis can be produced under various cultivation conditions discussed in this review, and their yields are relatively high when compared with those achieved in microalgal systems. Future challenges include achieving the economy of large-scale cultivation. Recent insights into the complex metabolism of E. gracilis have highlighted unique metabolic pathways, which could provide new leads for product enhancement by genetic modification of the organism. Also, development of molecular tools for strain improvement are emerging rapidly, making E. gracilis a noteworthy challenger for microalgae such as Chlorella spp. and their products currently on the market.

Critical Involvement of Environmental Carbon Dioxide Fixation to Drive Wax Ester Fermentation in Euglena

Accumulation profiles of wax esters in Euglena gracilis Z were studied under several environmental conditions. The highest amount of total wax esters accumulated under hypoxia in the dark, and C28 (myristyl-myristate, C14:0-C14:0) was prevalent among all conditions investigated. The wax ester production was almost completely suppressed under anoxia in the light, and supplying exogenous inorganic carbon sources restored wax ester fermentation, indicating the need for external carbon sources for the wax ester fermentation. 13C-labeling experiments revealed specific isotopic enrichment in the odd-numbered fatty acids derived from wax esters, indicating that the exogenously-supplied CO2 was incorporated into wax esters via the propionyl-CoA pathway through the reverse tricarboxylic acid (TCA) cycle. The addition of 3-mercaptopicolinic acid, a phosphoenolpyruvate carboxykinase (PEPCK) inhibitor, significantly affected the incorporation of 13C into citrate and malate as the biosynthetic intermediates of the odd-numbered fatty acids, suggesting the involvement of PEPCK reaction to drive wax ester fermentation. Additionally, the 13C-enrichment pattern of succinate suggested that the CO2 assimilation might proceed through alternative pathways in addition to the PEPCK reaction. The current results indicate that the mechanisms of anoxic CO2 assimilation are an important target to reinforce wax ester fermentation in Euglena.

Intermediate introns in nuclear genes of euglenids - are they a distinct type?

Background

Nuclear genes of euglenids contain two major types of introns: conventional spliceosomal and nonconventional introns. The latter are characterized by variable non-canonical borders, RNA secondary structure that brings intron ends together, and an unknown mechanism of removal. Some researchers also distinguish intermediate introns, which combine features of both types. They form a stable RNA secondary structure and are classified into two subtypes depending on whether they contain one (intermediate/nonconventional subtype) or both (conventional/intermediate subtype) canonical spliceosomal borders. However, it has been also postulated that most introns classified as intermediate could simply be special cases of conventional or nonconventional introns.

Results

Sequences of tubB, hsp90 and gapC genes from six strains of Euglena agilis were obtained. They contain four, six, and two or three introns, respectively (the third intron in the gapC gene is unique for just one strain). Conventional introns were present at three positions: two in the tubB gene (at one position conventional/intermediate introns were also found) and one in the gapC gene. Nonconventional introns are present at ten positions: two in the tubB gene (at one position intermediate/nonconventional introns were also found), six in hsp90 (at four positions intermediate/nonconventional introns were also found), and two in the gapC gene.

Conclusions

Sequence and RNA secondary structure analyses of nonconventional introns confirmed that their most strongly conserved elements are base pairing nucleotides at positions +4, +5 and +6/ -8, −7 and −6 (in most introns CAG/CTG nucleotides were observed). It was also confirmed that the presence of the 5' GT/C end in intermediate/nonconventional introns is not the result of kinship with conventional introns, but is due to evolutionary pressure to preserve the purine at the 5' end. However, an example of a nonconventional intron with GC-AG ends was shown, suggesting the possibility of intron type conversion between nonconventional and conventional. Furthermore, an analysis of conventional introns revealed that the ability to form a stable RNA secondary structure by some introns is probably not a result of their relationship with nonconventional introns. It was also shown that acquisition of new nonconventional introns is an ongoing process and can be observed at the level of a single species. In the recently acquired intron in the gapC gene an extended direct repeats at the intron-exon junctions are present, suggesting that double-strand break repair process could be the source of new nonconventional introns.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0620-5) contains supplementary material, which is available to authorized users.

Toxic effects of individual and combined effects of BTEX on Euglena gracilis

BTEX is a group of volatile organic compounds consisting of benzene, toluene, ethylbenzene and xylenes. Environmental contamination of BTEX can occur in the groundwater with their effects on the aquatic organisms and ecosystem being sparsely studied. The aim of this study was to evaluate the toxic effects of individual and mixed BTEX on Euglena gracilis (E. gracilis). We examined the growth rate, morphological changes and chlorophyll contents in E. gracilis Z and its mutant SMZ cells treated with single and mixture of BTEX. BTEX induced morphological change, formation of lipofuscin, and decreased chlorophyll content of E. gracilis Z in a dose response manner. The toxicity of individual BTEX on cell growth and chlorophyll inhibition is in the order of xylenes>ethylbenzene>toluene>benzene. SMZ was found more sensitive to BTEX than Z at much lower concentrations between 0.005 and 5 μM. The combined effect of mixed BTEX on chlorophyll contents was shown to be concentration addition (CA). Results from this study suggested that E. gracilis could be a suitable model for monitoring BTEX in the groundwater and predicting the combined effects on aqueous ecosystem.