Chloroplast and cytoplasmic ribosomes of Euglena: selective binding of dihydrostreptomycin to chloroplast ribosomes

An intact plastid genome is essential for the survival of colorless Euglena longa but not Euglena gracilis

Euglena gracilis growth with antibacterial agents leads to bleaching, permanent plastid gene loss. Colorless Euglena (Astasia) longa resembles a bleached E. gracilis. To evaluate the role of bleaching in E. longa evolution, the effect of streptomycin, a plastid protein synthesis inhibitor, and ofloxacin, a plastid DNA gyrase inhibitor, on E. gracilis and E. longa growth and plastid DNA content were compared. E. gracilis growth was unaffected by streptomycin and ofloxacin. Quantitative PCR analyses revealed a time dependent loss of plastid genes in E. gracilis demonstrating that bleaching agents produce plastid gene deletions without affecting cell growth. Streptomycin and ofloxacin inhibited E. longa growth indicating that it requires plastid genes to survive. This suggests that evolutionary divergence of E. longa from E. gracilis was triggered by the loss of a cytoplasmic metabolic activity also occurring in the plastid. Plastid metabolism has become obligatory for E. longa cell growth. A process termed "intermittent bleaching", short term exposure to subsaturating concentrations of reversible bleaching agents followed by growth in the absence of a bleaching agent, is proposed as the molecular mechanism for E. longa plastid genome reduction. Various non-photosynthetic lineages could have independently arisen from their photosynthetic ancestors via a similar process.

Chromium induced stress conditions in heterotrophic and auxotrophic strains of Euglena gracilis

Oxidative stress parameter and antioxidant defense compound as well as enzyme activity were studied in relation to different Cr(VI) concentrations (0, 10, 20, 40 μM) in two strains of Euglena gracilis, one isolated from a polluted river (MAT) and the other acquired from a culture collection (UTEX). Chromium toxicity was measured in the auxotrophic and obligated heterotrophic variants of the two strains. Chromium uptake was higher in auxotrophic cultures, reflected by their higher cell proliferation inhibition and lower IC50 levels compared to heterotrophic ones. In the Cr(VI) treatments a reduction of chlorophyll a and b ratio (Chl a/Chl b) was observed, the ratio of protein to paramylon content was augmented, and total lipid content increased, having the auxotrophic strains the highest values. TBARS content increased significantly only at 40 μM Cr(VI) treatment. Unsaturated fatty acids also increased in the Cr(VI) treatments, with the higher storage lipid (saturated acids) content in the heterotrophic cells. The antioxidant response, such as SOD activity and GSH content, increased with chromium concentration, showing the highest GSH values in the heterotrophic cultures and the SOD enzyme participation in chromium toxicity. The MAT strain had higher IC50 values, higher carbohydrate and saturated acid content, and better response of the antioxidant system than the UTEX one. This strain isolated from the polluted place also showed higher GSH content and SOD activity in control cells and in almost all treated cultures. SOD activity reached a 9-fold increase in both MAT strains. These results suggest that tolerance of MAT strain against Cr(VI) stress is not only related to GSH level and/or biosynthesis capacity but is also related to the participation of the SOD antioxidant enzyme.

Effects of streptomycin on growth of algae Chlorella vulgaris and Microcystis aeruginosa

Streptomycin is a common contaminant in a variety of industrial and agricultural wastewaters. The available information on the potential toxicity of streptomycin of fresh algae implicated in the treatment of biological wastewater is extremely limited. The objective of this study was to evaluate the effects of streptomycin on physiological indices and photosynthesis-related gene transcription. The results of short-term batch bioassays indicated that streptomycin was more sensitive to cyanobacteria than to green algae. The EC50 of streptomycin in Microcystis aeruginosa and Chlorella vulgaris were 0.28 and 20.08 mg L(-1) , respectively. These selected streptomycin concentrations inhibited algal cell growth and decreased chlorophyll or phycocyanobilin content. Streptomycin also destroyed the overall membrane system, which was speculated from malondialdehyde (MDA) content and electrolyte leakage increasing after streptomycin exposure. Two algae were induced to increase their antioxidant enzyme activities to withstand streptomycin. However, the balance between oxidant substance and antioxidant enzyme was broken, because reactive oxygen species (ROS) content simultaneously increased. Streptomycin inhibited photosynthesis-related gene transcription in C. vulgaris and M. aeruginosa. Transcript levels of psaB, psbA, and rbcL in C. vulgaris decreased to only 14.5%, 32.2%, and 9.3% of the control, respectively. Similarly, the transcript levels of psaB, psbD, and rbcL in M. aeruginosa decreased markedly in the present of streptomycin. The transcription of these genes was 12.4%, 26.1%, and 28.4% of the control after 0.1 mg L(-1) streptomycin exposure, respectively. Our results demonstrate that streptomycin is toxic to fresh algae, affects photosynthesis-related gene transcription, and blocks electron transport and ROS overproduction.

Chromium- and copper-induced inhibition of photosynthesis in Euglena gracilis analysed on the single-cell level by fluorescence kinetic microscopy

Here, we investigated effects of copper (Cu) and chromium (Cr) toxicity on two contrasting strains of Euglena gracilis, with and without chloroplasts, grown in culture media promoting either phototrophic or heterotrophic growth. This led to insights into Cr/Cu toxicity mechanisms and into the regulation of phototrophic vs heterotrophic metabolism. Our data strongly suggest that in Cu(2+) and Cr(6+) stressed Euglena photosynthesis is the primary target of damage. In the applied light conditions, this was mainly damage to the photosystem II reaction centre, as shown by single-cell measurements of photochemical fluorescence quenching. Respiration and photosynthetic dark reactions were less sensitive. The malfunctioning photosynthesis enhanced production of reactive oxygen species (mainly superoxide), leading to elevated amounts of carotenoid degradation products. At higher metal concentrations in chloroplast-containing cells, but not white cells, this oxidative stress resulted in increased respiratory oxygen uptake, likely by damage to mitochondria. During growth in nutrient solution promoting heterotrophic metabolism, the cells were able to repair the metal-induced damage to photosynthesis, moderating the inhibition of photochemistry. Growth in medium forcing the cells into photosynthesis increased the investment in photosynthetic pigments. Comparison of the two Euglena strains surprisingly showed that the previously metal-resistant strain lost this resistance during culture.

Gene expression patterns in Euglena gracilis: insights into the cellular response to environmental stress

To better understand Euglena gracilis gene expression under different stress conditions (Chromium, Streptomycin or darkness), we undertook a survey of the E. gracilis transcriptome by cDNA sequencing and microarray analysis. First, we constructed a non-normalized cDNA library from the E. gracilis UTEX strain and sequenced a total of 1000 cDNAs. Six hundred and ten of these ESTs were similar to either Plantae or Protistae genes (e-value<e(-10)). Second, microarrays were built by spotting all the ESTs onto mirror slides. Microarray expression analysis indicated that 90 out of those 610 ESTs changed their expression level in response to different stress treatments (p<0.05). In addition, we detected 10 ESTs that changed expression levels irrespective of the tested stress. These may be considered as part of a larger set of stress-related genes in E. gracilis. Finally, we identified 23 unknown ESTs (U-ESTs) following the expression profiles of these putative stress-related genes suggesting that they could be related to the cellular mechanism of stress response.

Cadmium-dependent generation of reactive oxygen species and mitochondrial DNA breaks in photosynthetic and non-photosynthetic strains of Euglena gracilis

The photosynthetic strain Z of Euglena gracilis is more susceptible to cadmium chloride (Cd) than the non-photosynthetic strain SMZ. We investigated the correlation of intracellular reactive oxygen species (ROS) levels with Cd-induced cellular damage. Flow cytometry with dihydrorhodamine 123 showed that strain Z generated higher levels of ROS, probably H(2)O(2) and/or ONOO(-), than strain SMZ, and that this difference between the two strains became more pronounced with increasing Cd dose. The levels of ROS increased at cytotoxic concentrations of Cd, at over 10 microM Cd for Z and 50 microM Cd for SMZ. These results show an association of Cd cytotoxicity with ROS generation. Considering that strain SMZ is non-photosynthetic, the higher levels of ROS in strain Z might be due to blockage of photosynthetic electron flow by Cd. Using terminal deoxyribonucleotidyl transferase-mediated dUTP nick end-labeling analysis in combination with 4',6-diamidino-2-phenylindole, dihydrochloride staining, we observed DNA breaks in the mitochondria of both strains after Cd exposure. The results suggest that the mitochondrion is the primary target organelle of Cd in E. gracilis cells.

The enigma of the gene coding for ribosomal protein S12 in the chloroplasts of Nicotiana

A 2.9 kbp region from within the inverted repeat of Nicotiana chloroplast DNA hybridized with a chloroplast DNA fragment from Euglena containing the complete rps12 gene coding for ribosomal protein S12. Nucleotide sequencing within this region revealed the existance of two rps12 coding stretches interrupted by 540 bp having class II intron structure. Joining and decoding the exon regions produced a sequence of 85 amino acids colinear and 81% homologous to the S12 protein of Euglena chloroplasts and E. coli, starting from amino acid residue 38 to the stop codon. Immediately upstream of codon 38, conserved intron sequences were located. However, the 5' 37 codon of Nicotiana chloroplast rps12 could not be identified by electron microscopy of RNA-DNA hybrids within a DNA region extending 4000 bp upstream of codon 38, nor by computer search of a completely sequenced region extending for more than 9000 bp upstream of this codon. In E. coli, alteration in rps12 codons 42 or 87 causes streptomycin resistance. However, the nucleotide sequence of the identified rps12 exons in two Nicotiana chloroplast mutants resistant to streptomycin were found to be identical to that of wild type.

Influence of photosynthesis and chlorophyll synthesis on polypeptide accumulation in greening euglena

Two-dimensional gel electrophoresis resolves total cellular protein from Euglena gracilis klebs var bacillaris Cori into 640 polypeptides, 79 of which are induced by light exposure. The inhibition of chloroplast translation by streptomycin, the direct inhibition of photosynthesis as well as the indirect inhibition of chlorophyll synthesis by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and the specific inhibition of photosynthesis but not chlorophyll synthesis by DCMU in the presence of 17 millimolar ethanol failed to inhibit the accumulation of 40 polypeptides. These polypeptides appear to be synthesized on cytoplasmic ribosomes and their accumulation is independent of the developmental status of the chloroplast. Streptomycin but not DCMU completely inhibited the accumulation of six polypeptides which are undetectable in mutants lacking chloroplast DNA suggesting that these polypeptides are translated on chloroplast ribosomes. The accumulation of seven polypeptides which are detectable in mutants lacking chloroplast DNA was also inhibited by streptomycin but not by DCMU suggesting that the accumulation of these polypeptides is dependent upon stabilization by a chloroplast translation product. The accumulation of 12 polypeptides was inhibited by streptomycin and by DCMU under conditions in which chlorophyll synthesis was inhibited, but not under conditions in which chlorophyll synthesis was unaffected by DCMU. The inhibition by DCMU of the accumulation of these polypeptides appears to be due to the inhibition of chlorophyll synthesis suggesting that they are components of pigment protein complexes. The accumulation of six polypeptides was inhibited under all conditions in which photosynthesis was inhibited suggesting that the accumulation of these polypeptides is dependent upon a product of photosynthesis.

The genes for the ribosomal proteins S12 and S7 are clustered with the gene for the EF-Tu protein on the chloroplast genome of Euglena gracilis

We characterize a DNA segment of the Euglena gracilis chloroplast DNA fragment Eco . N by nucleotide sequencing and S1 nuclease analysis. We show that this region, which is upstream of the previously sequenced tuf A gene, contains the genes for the ribosomal proteins S12 and S7. The gene arrangement is 5'-rps 12-80 bp spacer-rps 7-174 bp spacer-tuf A, somewhat similar to the str operon of E. coli. The chloroplast S12 and S7 proteins contain 124 and 155 aminoacids, respectively, and are to 68% and 38% homologous with the corresponding E. coli proteins. The region is transcribed into a distronic mRNA of about 1.1 to 1.2 kb. The rps 12 and rps 7 genes, contrary to the tuf A gene, are not split.

Functional and Structural Organization of Chlorophyll in the Developing Photosynthetic Membranes of Euglena gracilis Z: III. SEQUENCE OF EVENTS LEADING TO THE FORMATION OF FUNCTIONAL PHOTOSYSTEM II PHOTOSYNTHETIC UNITS

Greening cells of Euglena were transferred back to darkness at different stages of chloroplast development in the presence or absence of specific inhibitors of protein synthesis. The analysis of chloroplast components showed that: (a) cycloheximide or streptomycin does not significantly inhibit the formation in darkness of active photosystem II (PSII) reaction centers if added after the lag phase for chloroplast development; (b) a limited number of active reaction centers are formed in the dark, sufficient to increase PSII reaction center to chlorophyll ratios to values close to those found in fully greened cells; (c) these dark-formed reaction centers appear to be inserted in already constituted and complete light-harvesting antennae. These results complement previous ones and lead us to propose a model for a sequential formation of PSII photosynthetic units during greening of Euglena, whereby conformational changes requiring time would allow already synthesized components of PSII reaction centers to be inserted or reorganized as active photochemical complexes in association with previously formed light-harvesting antennae.

Events surrounding the early development of Euglena chloroplasts. 16. Plastid thylakoid polypeptides during greening

Using sulfolipid to locate plastid thylakoid membranes in gradients from dark-grown resting cells it has been possible to study the plastid thylakoid membrane polypeptides of Euglena gracilis var. bacillaris undergoing light-induced chloroplast development. All plastid thylakoid bands seen in dark-growing wild-type cells and in mutant W3BUL in which plastid DNA is undetectable, are observed to increase in amount during plastid development. Others, which are undetectable in dark-grown wild-type and W3BUL increase greatly during plastid development and appear to be those associated with pigment-protein complexes. The data obtained from experiments where the polypeptides were labeled with 35S during development, either continuously or in pulses, were consistent with these findings. Cycloheximide strongly inhibited the increases in amount in all bands and chloramphenicol or streptomycin produced a lower level of inhibition in all bands indicating tight control of theformation of each plastid membrane constituent by the others. The formation of a polypeptide band of 25 000 molecular weight, thought to be a part of a pigment-protein complex of the thylakoid, and chlorophyll synthesis were inhibited identically by these antibiotics.

Events Surrounding the Early Development of Euglena Chloroplasts: 14. Biosynthesis of Cytochrome c-552 in Wild Type and Mutant Cells

Lack of a suitable assay has thwarted attempts to measure cytochrome c-552 in dark-grown wild type cells of Euglena gracilis var. bacillaris in mutants and in other situations where the concentrations are low. Purification methods are described based on electrofocusing which provide a cytochrome c-552 preparation homogeneous enough to elicit a single reactive antibody in rabbits; this antibody is then used as a specific and sensitive assay for cytochrome c-552. Dark-grown cells of wild type and of mutants O(1)BS, O(2)BX, G(1)BU and P(1)BXL (which make normal sized chloroplasts with abnormal internal structure in the light) have 0.02 to 0.1 x 10(-11) micromoles of cytochrome c-552 per cell, 10 to 150 times less than light-grown cells. Light-grown cells of these mutants and of wild type show a ratio of chlorophyll to cytochrome of about 300 (mole to mole). Cytochrome c-552 is undetectable in dark-grown Y(1)BXD, Y(3)BUD, and W(34)ZUD which cannot carry plastid development beyond the proplastid in light; the light-grown cells of these mutants have levels of cytochrome similar to or lower than dark-grown wild type cells. Cytochrome c-552 is undetectable in light- and dark-grown mutants in which plastid DNA is undetectable (such as Y(2)BUL, W(3)BUL, W(8)BHL, and W(10)BSmL) consistent with the view, but not proving, that this molecule may be coded, at least in part, in plastid DNA. During light-induced chloroplast development in resting cells, cytochrome c-552 formation behaves in all respects like chlorophyll except that the dark-grown cells contain low amounts of the cytochrome c-552 but lack chlorophyll. Thus, both cytochrome c-552 and chlorophyll show the same lag period even when the length is changed by nutritional manipulation; preillumination largely eliminates the lag in the formation of both molecules, cycloheximide and streptomycin both inhibit the biosynthesis of chlorophyll and cytochrome c-552 in the same manner, and the formation of both during chloroplast development is strictly light-dependent. It is shown that chloroplasts isolated from Euglena by methods thought to give intact organelles, lack 95% of the cytochrome c-552; this and the loss of similar molecules may explain why these isolated chloroplasts are not photosynthetically active.

Characterization of cytoplasmic and chloroplast ribosomal proteins of Euglena gracilis

Active cytoplasmic ribosone subunits 41 and 62S were prepared by treatment with 0.1 mM puromycin in the presence of 265 mM KCl. Active chloroplast subunits 32 and 49S were obtained after dialysis of chloroplast ribosomal preparations against 1 mM Mg(2+)-containing buffer. Proteins from these different ribosomal particles were mapped by two-dimensional gel electrophoresis in the presence of urea. The 41S small cytoplasmic ribosomal subunit contains 33-36 proteins, the 62S large cytoplasmic ribosomal subunit contains 37-43, the 32S small chloroplast ribosomal subunit contains 22-24, and the 49ts large chloroplast ribosomal subunit contains 30-34 proteins. Since some proteins are lost during dissociation of monosomes into subunits, the 89S cytoplasmic monosome would have 73-83 proteins and the 68S chloroplast monosome, 56-60. The amino acid composition of ribosomal proteins shows differences between chloroplast and cytoplasmic ribosomes.

Comments on the translational and transcriptional origin of Euglena chloroplastic aminoacyl-tRNA synthetases

A response to: "A consideration of Euglena gracilis W3BUL as a cytoplasmic control for the wild-type phenylalanyl-tRNA synthetase system" and "A reinvestigation of the sites of transcription and translation of Euglena chloroplastic phenylalanyl-tRNA synthetase" by J. L. Lesiewicz and D. S. Herson.

Events Surrounding the Early Development of Euglena Chloroplasts: VII. Photocontrol of the Source Of Reducing Power for Chloramphenicol Reduction by the Ferredoxin-NADP Reductase System

d(-)threo-Chloramphenicol blocks chlorophyll and plastid protein synthesis in Euglena. During chloroplast development in white light, but not in red, the cells escape from chloramphenicol inhibition and chlorophyll formation is restored. Concomitantly, chloramphenicol is reduced. Reduction of chloramphenicol in an enzyme extract from Euglena requires NADPH and ferredoxin for maximal activity. Methyl viologen replaces ferredoxin, and when chemically reduced, ferredoxin or methyl viologen reduces chloramphenicol directly. This suggests that the enzyme involved is ferredoxin-NADP reductase. In agreement, crude extracts from wild type and W(3)BUL, a mutant lacking detectable plastids and plastid DNA, when separated on acrylamide gels, show a single band which reduces methyl viologen with NADPH, and its mobility is similar in wild type and in mutant W(3)BUL. The reductase is inducible by light and increases 3-fold in wild type in white or red light and 1.5-fold in W(3)BUL in white light. DCMU does not block chloramphenicol reduction in vivo indicating that electrons originate from sources other than photosynthetic electron transport. We infer that chloramphenicol is reduced by ferredoxin which receives electrons via ferredoxin-NADP reductase. The limiting step is not the enzyme but the source of reducing power which can be supplied from the cytoplasm, probably under control of the blue light receptor. Ferredoxin and ferredoxin NADP reductase appear to be coded in the nuclear genome, synthesized on cytoplasmic ribosomes, and join a group of enzymes which cannot be precisely localized, since they may be active anywhere from their site of synthesis in the cytoplasm to their place of deposition in the chloroplast.

Biosynthetic events required for lag elimination in chlorophyll synthesis in Euglena

Levulinic acid, a competitive inhibitor of δ aminolevulinic acid dehydratase, cycloheximide, an inhibitor of translation on 89s cytoplasmic ribosomes, and chloramphenicol, an inhibitor of translation on 68s chloroplast ribosomes, are reversible inhibitors of light induced chlorophyll synthesis in resting Euglena gracilis Klebs. When dark grown resting cells are preilluminated for 2 h followed by darkness for 12 h prior to exposure to continuous light, the usual lag period in chlorophyll formation is eliminated. If cycloheximide, chloramphenicol, or levulinic acid are present during either the preillumination period or the subsequent dark period, the lag is reestablished. Only the very beginning of the dark period is sensitive to cycloheximide but the dark period is less sensitive to levulinic acid than is the light period. Exposure of preilluminated cells to cycloheximide or levulinic acid at the time of exposure to continuous illumination completely inhibits chlorophyll synthesis indicating that the potential for rapid chlorophyll synthesis generated by preillumination and a dark period does not result simply from the accumulation of porphyrin precursors. Preillumination has little effect on the development of the capacity to fix CO2 photosynthetically. These results indicate that the control of chlorophyll formation is more complex than in higher plants and a model based on the formation of certain crucial enzymes in the porphyrin pathway, rather than simply upon the accumulation of δ aminolevulinic acid is presented to explain the experimental findings.

Inhibition of chloroplast development in Euglena by streptomycin: Differential inhibition of the appearance of photosynthesis in the presence of the continued synthesis of chlorophyll

Streptomycin effectively inhibits chloroplast development in dark-grown non-dividing Euglena gracilis when added at the onset of greening but apparently exerts a diminished effect on chlorophyll synthesis when added at later stages. We have further investigated this phenomenon and show that streptomycin added to a Euglena culture at 24 h of development has a differential inhibitory action on the extent of synthesis of several chloroplast-associated parameters. Chlorophyll, carotenoids, cytochrome 552 and photosystem I Hill activity are all slightly, if at all, inhibited and to approximately the same extent between 24 and 72 h of development. We find a very strong inhibition of both ribulose diphosphate carboxylase synthesis and photosystem II Hill activity.