Chlorella Research Articles

Homology modeling and docking studies of FabH (β-ketoacyl-ACP synthase III) enzyme involved in type II fatty acid biosynthesis of Chlorella variabilis: a potential algal feedstock for biofuel production

The concept of using microalgae as an alternative renewable source of biofuel has gained much importance in recent years. However, its commercial feasibility is still an area of concern for researchers. Unraveling the fatty acid metabolic pathway and understanding structural features of various key enzymes regulating the process will provide valuable insights to target microalgae for augmented oil content. FabH (β-ketoacyl-acyl carrier protein synthase; KAS III) is a condensing enzyme catalyzing the initial elongation step of type II fatty acid biosynthetic process and acyl carrier protein (ACP) facilitates the shuttling of the fatty acyl intermediates to the active site of the respective enzymes in the pathway. In the present study, a reliable three-dimensional structure of FabH from Chlorella variabilis, an oleaginous green microalga was modeled and subsequently the key residues involved in substrate binding were determined by employing protein–protein docking and molecular dynamics (MD) simulation protocols. The FabH-ACP complex having the lowest docking energy score showed the binding of ACP to the electropositive FabH surface with strong hydrogen bond interactions. The MD simulation results indicated that the substrate-complexed FabH adopted a more stable conformation than the free enzyme. Further, the FabH structure retained its stability throughout the simulation although noticeable displacements were observed in the loop regions. Molecular simulation studies suggested the importance of crucial hydrogen bonding of the conserved Arg91 of FabH with Glu53 and Asp56 of ACP for exhibiting high affinity between the enzyme and substrate. The molecular modeling results are consistent with available experimental results on the flexibility of FabH and the present study provides first in silico insights into the structural and dynamical aspect of catalytic mechanism of FabH, which could be used for further site-specific mutagenic experiments to develop engineered high oil-yielding microalgal strains for biofuel production.

Phycodnavirus potassium ion channel proteins question the virus molecular piracy hypothesis.

Phycodnaviruses are large dsDNA, algal-infecting viruses that encode many genes with homologs in prokaryotes and eukaryotes. Among the viral gene products are the smallest proteins known to form functional K+ channels. To determine if these viral K+ channels are the product of molecular piracy from their hosts, we compared the sequences of the K+ channel pore modules from seven phycodnaviruses to the K+ channels from Chlorella variabilis and Ectocarpus siliculosus, whose genomes have recently been sequenced. C. variabilis is the host for two of the viruses PBCV-1 and NY-2A and E. siliculosus is the host for the virus EsV-1. Systematic phylogenetic analyses consistently indicate that the viral K+ channels are not related to any lineage of the host channel homologs and that they are more closely related to each other than to their host homologs. A consensus sequence of the viral channels resembles a protein of unknown function from a proteobacterium. However, the bacterial protein lacks the consensus motif of all K+ channels and it does not form a functional channel in yeast, suggesting that the viral channels did not come from a proteobacterium. Collectively, our results indicate that the viruses did not acquire their K+ channel-encoding genes from their current algal hosts by gene transfer; thus alternative explanations are required. One possibility is that the viral genes arose from ancient organisms, which served as their hosts before the viruses developed their current host specificity. Alternatively the viral proteins could be the origin of K+ channels in algae and perhaps even all cellular organisms.

Cell division and density of symbiotic Chlorella variabilis of the ciliate Paramecium bursaria is controlled by the host's nutritional conditions during early infection process

The association of ciliate Paramecium bursaria with symbiotic Chlorella sp. is a mutualistic symbiosis. However, both the alga-free paramecia and symbiotic algae can still grow independently and can be reinfected experimentally by mixing them. Effects of the host's nutritional conditions against the symbiotic algal cell division and density were examined during early reinfection. Transmission electron microscopy revealed that algal cell division starts 24 h after mixing with alga-free P. bursaria, and that the algal mother cell wall is discarded from the perialgal vacuole membrane, which encloses symbiotic alga. Labelling of the mother cell wall with Calcofluor White Stain, a cell-wall-specific fluorochrome, was used to show whether alga had divided or not. Pulse labelling of alga-free P. bursaria cells with Calcofluor White Stain-stained algae with or without food bacteria for P. bursaria revealed that the fluorescence of Calcofluor White Stain in P. bursaria with bacteria disappeared within 3 days after mixing, significantly faster than without bacteria. Similar results were obtained both under constant light and dark conditions. This report is the first describing that the cell division and density of symbiotic algae of P. bursaria are controlled by the host's nutritional conditions during early infection.

기수산 물벼룩의 배양을 위한 대체 먹이원 내 EPA 영향

We investigated the effect on dietary EPA (eicosapentaenoic acid) source (EP) into formulated diets for growth of brackish flea, Diaphanosoma celebensis. The highest density and specific growth rate (SGR) of brackish fleas were observed on Tetraselmis suecica (TE) trial, but these of trial were not significantly differed with that of Chlorella (CH) + Crypthecodinium sp. (CR) + EP trial, contained EPA oil (P>0.05). Contrastively, CH trial showed the lowest SGR. And in the RNA/DNA ratio, 0.08 of TE trial was the highest ratio out of whole trials, but the trial not significantly differed with that of CH + CR + EP trial (P>0.05). But, the ratio of CH trial was the lowest ratio at 0.05 out of whole trials (P<0.05). Through out results, the EPA source for flea culture was showed a positive effect through their growth and SGR. Therefore, we suggested that a usage of the source with CH could replace T. suecica as good diet for culture of the brackish flea.

Photobiont Flexibility in &amp;lt;i&amp;gt;Paramecium bursaria&amp;lt;/i&amp;gt;: Double and Triple Photobiont Co-Habitation

The green ciliate, Paramecium bursaria, has evolved a mutualistic relationship with endosymbiotic green algae (photobionts). Under culture conditions, photobionts are usually unified (to be single species) within each P. bursaria strain. In most cases, the algal partners are restricted to either Chlorella variabilis or Micractinium reisseri (Chlorellaceae, Trebouxiophyceae). Both species are characterized by particular physiology and atypical group I intron insertions, although they are morphologically indistinguishable from each other or from other Chlorella-related species. Both algae are exclusive species that are viable only within P. bursaria cells, and therefore their symbiotic relationship can be considered persistent. In a few cases, the other algal species have been reported as P. bursaria photobionts. Namely, P. bursaria have occasionally replaced their photobiont partner. This paper introduces some P. bursaria strains that maintain more than one species of algae for a long period. This situation prompts speculations about flexibility of host-photo-biont relationships, how P. bursaria replaced these photobionts, and the infection theory of the group I introns.

Study of physical chemistry on biosorption of zinc by using Chlorella pyrenoidosa

Discharge of heavy metals from metal processing industries is known to have adverse effects on the environment. Biosorption of heavy metals by metabolically inactive biomass of microbial organisms is an innovative and alternative technology for removal of these pollutants from aqueous solution. Presence of heavy metals in the aquatic system is posing serious problems and zinc has been used in many industrials and removal of Zn ions from waste waters is significant. Biosorption is one of the economic methods that is used for removal of heavy metals. In the present study, the biomass generated from the dried Chlorella pyronoidsa was used for evaluating the biosorption characteristics of Zn ions in aqueous solutions. Batch adsorption experiments were performed on these leaves and it was found that the amount of metal ions adsorbed increased with the increase in the initial metal ion concentration. In this study effect of agitation time, initial metal ion concentration, temperature, pH and biomass dosage were studied. Maximum metal uptake was observed at pH = 5. Maximum metal uptake (qmax) was 101.11 mg/g. The biosorption followed both Langmuir and Freundlich isotherm model. The adsorption equilibrium was reached in about 1 h. The kinetic of biosorption followed the second – order rate. The biomass could be regenerated using 0.1 M HNO3. A positive value of ∆H° indicated the endothermic nature of the process. A negative value of the free energy (∆G°) indicated the spontaneous nature of the adsorption process. A positive value of ∆S° showed increased randomness at solid–liquid interface during the adsorption of heavy metals, it also suggests some structural changes in the adsorbate and the adsorbent.Fourier transform infrared (FTIR) spectrums of C. pyrenoidosa revealed the presence of hydroxyl, amino, carboxylic and carbonyl groups. The scanning electron micrograph (SEM) clearly revealed the surface texture and morphology of the biosorbent. Key words: Biosorption, Chlorella pyronoidosa, Zn, isotherm models, kinetic.

Studies on the growth behavior of Chlorella, Haematococcus and Scenedesmus sp. in culture media with different concentrations of sodium bicarbonate and carbon dioxide gas

Growth studies were conducted on green algae Chlorella, Scenedesmus andHaematococcus strains in batch mode cultures. In this study, the effect of sodium bicarbonate salt (NaHCO3) and carbon dioxide (CO2) gas as carbon source on microalgal cultures were investigated. For this purpose, growth response of theaforementioned three strains under varying concentrations of NaHCO3 (15, 30, 45, 60 and 75 mg/L,) and CO2 gas (7929, 4758 and 4400 mg/L,) were investigated. The best growth response showed by chlorella strain was observed at 75 mg/L (ppm) bicarbonate (% increase in biomass=82.6mg/L/day for 12 days) and 4758 mg/L CO2 gas concentration (189.1 mg/L/day for 7 days). While Haematococcus strain showed its best growth in 30 ppm bicarbonate (72.9 mg/L/day for 17 days) and 4758 mg/L CO2 gas (134.1 mg/L for 7 days), the Scenedesmus strain showed its best growth in 45 ppm bicarbonate (30.9 mg/L/day for 17 days) and 4758 mg/L CO2gas (103.8 mg/L for 7 days). All the strains showed good growth when CO2 gas was supplied in terms of increase in cell number, biomass and lipid content compared to bicarbonate utilization as carbon source, except Haematococcusstrain which fail to grow when high concentration of CO2 gas (7929 ppm) was supplied. Out of the three strains, it was Chlorella sp. which showed highest growth rate and lipid content when CO2 gas was supplied, (specific growth=0.704; 189.1% increase in biomass, g/L/day and 1.015 doubling/day, 31% lipid content in terms of dry cell weight). Key words: Microalgae, bicarbonate, biomass, lipid.

Effects of selective medium on lipid accumulation of chlorellas and screening of high lipid mutants through ultraviolet mutagenesis

Two micro-algae Y019 and Y041 were isolated from tropical fresh water in Hainan, China. Throughphylogenetic analysis of 18S rDNA sequences, they had been identified as Chlorella vulgaris and Chlorella pyrenoidosa. Subsequently, both of them and C. vulgaris FACHB-31 were cultured respectively in four selective medium (SE, BG11, HSM1, DS) at 25°C, 230 r/min, 24 h full light[z1], 50-110 μE/m2/s. Effects of these media on the cell growth and lipid content were detected. The results showed that, the HSM1 medium is more suitable for the growth of Chlorella, while the DS medium is more conducive to the lipid accumulation. In the DS medium, the lipid content of C. vulgaris Y019 was 1.84 ~ 2.64-fold than others at 12 days. So the local separated algae C. vulgaris Y019 is thought of an ideal raw material for biodiesel production. After that, we conducted Ultraviolet mutagenesis for C. vulgaris Y019. A total of 1086 algae strains had been screened for lipid production in HSM and HSM-N media.. Results showed: in HSM medium, mutants Y019-M57 and Y019-M66 were identified as high lipid producing mutants, while in HSM-N medium Y019-M67 was detected as high lipid content mutants. These mutants laid the foundation for further research and commercial application. Key words: Chlorella, culture medium, Ultraviolet mutants, lipid accumulation.

Growth, survival and proximate body composition of Labeo rohita larvae fed artificial food and natural food organisms under laboratory condition

This investigation was carried out to study the effect of different live feed and dry feed on growth and survival of Labeo rohita at a stocking density of 20 larvae per trough having 10 L of water. The increase in weights and lengths were used as measures of growth. The duration of the experiment was 30 days. Seven dietary treatments were tested viz. Artificial diet with 45% protein (LFr1), rotifers like Asplanchna and Brachionus (LFr2), wild zooplankton (LFr3), bioenriched zooplankton (raised on Chlorella , cod liver oil and vitamin C) (LFr4), Artemia (LFr5), Chironomous (LFr6) and Oligochaetes (LFr7). Among the different treatments, larvae fed with diet LFr4 resulted in the maximum body weight gain (BWG) (13.18 ± 0.13 mg) which was significantly (P < 0.05) higher than all the treatments which followed the order of preference as: LFr5 (12.31 ± 0.10 mg), LFr3 (9.75 ± 0.08 mg), LFr2 (7.85 ± 0.10 mg), LFr7 (6.49 ± 0.15 mg), LFr6 (5.66 ± 0.13 mg) and LFr1 (4.99 ± 0.14 mg). The diet LFr4 recorded maximum survivability (92.0 ± 2.0%). All the values recorded for the BWG and survival were found to be significantly different (P < 0.05) among others. Protein and lipid content of the prawn after the treatment was found to be highest for LFr5 and LFr4, respectively.

Aquatic toxicity of various pharmaceuticals on some isolated plankton species

Four drugs belonging to different therapeutic classes were chosen to examine their toxicity on some plankton organisms of different trophic levels. They include algae (Chlorella vulgaris and Ankestrodesmus falcatus), protozoa (Paramecium caudatum), rotifers (Brachionus calyciflorus) and cladocerans (Daphnia longispina). The tested drugs are erythromycin (antibiotic), fluoxetine (antidepressant), naproxen (a nonsteroidal anti-inflammatory) and gemfibrozil (lipid regulator). Algae were found to be more sensitive than other tested species to all tested drugs. The antibiotic erythromycin seriously affected the tested organisms even at low concentrations causing remarkable drop in their growth rates compared to the Control of each species. The acute exposure to fluoxetine during the present experiment exerted dramatic effect on both tested algae, with average LC50 values of 36 and 40 µg l-1for A. falcatus and C. vulgaris, respectively. On the contrary, fluoxetine enhanced the growth rates for both B. calyciflorus and D. longispina at low concentrations. P. caudatum was the most sensitive species to naproxen exposure, recording the lowest average LC50 value of 36 mg l-1 among the tested species after 24 h. Gemfibrozil had the least effect on the tested aquatic organisms with average LC50 values ranging between a minimum value of 56 mg l-1recorded for A. falcatus and 78 mg l-1 for B. calyciflorus. All the tested organisms suffered from oxidative stress in different degrees as a result of drug exposure. Our results showed reduction in the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) activities and elevation in lipid peroxidation (TBARS) levels in all tested species after exposure when compared with their activities in the control group. The results presented in this study suggest that the drugs investigated have toxic effects on the aquatic organisms tested. We concluded that there is a potential risk for non-target organisms associated with low levels of pharmaceuticals in surface waters. Chronic responses of non-target biota are not fully expected. Therefore, safe ways of discarding drug residues should be developed in order to protect the aquatic fauna. Key words: Catalase, lipid peroxidation, algae, zooplankton, pharmaceuticals.

Evolutionary significance of an algal gene encoding an [FeFe]-hydrogenase with F-domain homology and hydrogenase activity in Chlorella variabilis NC64A

[FeFe]-hydrogenases (HYDA) link the production of molecular H(2) to anaerobic metabolism in many green algae. Similar to Chlamydomonas reinhardtii, Chlorella variabilis NC64A (Trebouxiophyceae, Chlorophyta) exhibits [FeFe]-hydrogenase (HYDA) activity during anoxia. In contrast to C. reinhardtii and other chlorophycean algae, which contain hydrogenases with only the HYDA active site (H-cluster), C. variabilis NC64A is the only known green alga containing HYDA genes encoding accessory FeS cluster-binding domains (F-cluster). cDNA sequencing confirmed the presence of F-cluster HYDA1 mRNA transcripts, and identified deviations from the in silico splicing models. We show that HYDA activity in C. variabilis NC64A is coupled to anoxic photosynthetic electron transport (PSII linked, as well as PSII-independent) and dark fermentation. We also show that the in vivo H(2)-photoproduction activity observed is as O(2) sensitive as in C. reinhardtii. The two C. variabilis NC64A HYDA sequences are similar to homologs found in more deeply branching bacteria (Thermotogales), diatoms, and heterotrophic flagellates, suggesting that an F-cluster HYDA is the ancestral enzyme in algae. Phylogenetic analysis indicates that the algal HYDA H-cluster domains are monophyletic, suggesting that they share a common origin, and evolved from a single ancestral F-cluster HYDA. Furthermore, phylogenetic reconstruction indicates that the multiple algal HYDA paralogs are the result of gene duplication events that occurred independently within each algal lineage. Collectively, comparative genomic, physiological, and phylogenetic analyses of the C. variabilis NC64A hydrogenase has provided new insights into the molecular evolution and diversity of algal [FeFe]-hydrogenases.

Ecotoxicology tests on microalgae from Crdoba, Argentina

The eutrophication process involves important changes in the normal characteristics of water quality that may alter the balance between organisms. Microalgae particularly are very sensitive to changes. International standarized protocols were developed in order to detect water contaminants by their effects on microalgae, but it is important to evaluate contaminants over native species in our ecosystems. Using potassium dicromate as reference toxic, three native species were tested and one used in international protocols. Results showed that Chlorella vulgaris was the most sensitive organism both in acute tests and in chronic tests, and it happened even at concentrations below the levels permitted by environmental legislation. The use of biological tests as a complementary methodology for physical and chemical analysis is relevant when dealing with problems involving water quality. Key words: Ecotoxicology, microalgae, water quality.

Optimization of abiotic conditions suitable for the production of biodiesel from Chlorella vulgaris

The present study reports the production of fatty acids by microalgae under the influence of light and dark condition. Microalgae are renewable resource containing rich lipids in their body and has the potential to refill the partial energy demands in an eco-friendly way. We isolated an indigenous green alga ( Chlorella vulgaris ) as a potent source for biodiesel. To get better yield of biofuel, the growth of the microalgal isolate was optimized with the addition of nutrients and salts under light and dark conditions. The lipid fractions were extracted from the biomass through solvent extractions and the fractions were analyzed for biodiesel under GC-MS. The percentage of lipids synthesized from C. vulgaris under light and dark conditions were analyzed and compared. The algae from dark sample shows rich in saturated fatty acid (capric acid, lauric acid&myristic acid) and considerable amount of PUFA (hexadecatrienoic acid, stearidonic acid, eicosapenaenoic acid, docosahexaenoic acid) when compare to algae grown under light. So the algae grown in dark condition is an excellent source for high yield of saturated fatty acids.

The effects of nutritional restriction on neutral lipid accumulation in Chlamydomonas and Chlorella

Under nutrient starvation conditions, many microalgae are known to accumulate triacylglycerols (TAG) that can be used for biodiesel production. However, few studies have been performed to analyze the effect of deficiency in nutrient elements such as sulfur, phosphorus, potassium, iron, magnesium and calcium on oil production, particularly in Chlamydomonas and Chlorella. In this study, we investigated lipid content of Chlamydomonas reinhaditti CC124 and Chlorella vulgaris Y-019 grown in TAP, HSM, BG11, SE lacking optimal concentrations of these elements. Our results showed that, in high carbon HSM and TAP media, N and S starvation led to significant increase in cellular lipid content in both microalgae species. In addition, C. reinhaditti grown in TAP media without P, Fe, K, Ca or Mg or in HSM media without K, Ca or Mg also accumulated detectably higher neutral lipids. In contrast, in C. vulgaris, such accumulation was observed only in Mg-free and Fe-free HSM media. In low carbon SE and BG11 media, N starvation resulted in a moderate increase in the lipids content both in C. reinhaditti and C. vulgaris. On the other hand, P, S, K, Ca or Mg deficiency promoted neutral lipids accumulation in C. vulgaris. Finally, we analyzed and discussed the relationships among cell growth rate, lipid accumulation and nitrogen concentrations in C. reinhaditti. Key words: Nutrient limitation, lipid accumulation, nitrogen, sulfur, phosphorus, potassium, iron, magnesium, calcium.

The adaptability of three Arctic microalgae to different low temperatures

In order to study the adaptability of Arctic microalgae to different environmental temperatures, the growth curves and antioxidase system of three microalgae ( Skeletonema marinoi , Chlorella  sp. and Chlamydomonas sp.) that were separated from the Ny-Alesund, the high Arctic, at different low temperatures (0℃, 4℃ and 8℃) were determined. The result showed that the adaptability of the microalgae to temperatures depended on the species. The growth rate, SOD and CAT activities of Skeletonema marinoi were the highest at 4℃, but MDA content was the lowest. The growth rate and enzyme activity of Chlorella sp. were the highest at 8℃, while the lowest MDA content presented at 0℃. The growth of Chlamydomonas sp. at the different temperatures was not so significant, the lowest MDA content presented at 8℃. The change of antioxidase system also depended on species and temperatures. Three indexes of antioxidase system of Skeletonema marinoi between 0℃ and 4℃ showed extremely significant difference (p Skeletonema marinoi and Chlorella sp.between 0℃ and 8℃ showed significant difference (p Chlamydomonas sp. at the three temperatures differed insignificantly. In conclusion, the three microalgae had good adaptability to the three temperatures; their MDA content presented a low level, and had unique physiological mechanism to adapt to the environment with different low temperatures.

An in silico analysis of the mitochondrial protein import apparatus of plants.

BackgroundAn in silico analysis of the mitochondrial protein import apparatus from a variety of species; including Chlamydomonas reinhardtii, Chlorella variabilis, Ectocarpus siliculosus, Cyanidioschyzon merolae, Physcomitrella patens, Selaginella moellendorffii, Picea glauca, Oryza sativa and Arabidopsis thaliana was undertaken to determine if components differed within and between plant and non-plant species.ResultsThe channel forming subunits of the outer membrane components Tom40 and Sam50 are conserved between plant groups and other eukaryotes. In contrast, the receptor component(s) in green plants, particularly Tom20, (C. reinhardtii, C. variabilis, P. patens, S. moellendorffii, P. glauca, O. sativa and A. thaliana) are specific to this lineage. Red algae contain a Tom22 receptor that is orthologous to yeast Tom22. Furthermore, plant mitochondrial receptors display differences between various plant lineages. These are evidenced by distinctive motifs in all plant Metaxins, which are absent in red algae, and the presence of the outer membrane receptor OM64 in Angiosperms (rice and Arabidopsis), but not in lycophytes (S. moellendorffii) and gymnosperms (P. glauca). Furthermore, although the intermembrane space receptor Mia40 is conserved across a wide phylogenetic range, its function differs between lineages. In all plant lineages, Tim17 contains a C-terminal extension, which may act as a receptor component for the import of nucleic acids into plant mitochondria.ConclusionsIt is proposed that the observed functional divergences are due to the selective pressure to sort proteins between mitochondria and chloroplasts, resulting in differences in protein receptor components between plant groups and other organisms. Additionally, diversity of receptor components is observed within the plant kingdom. Even when receptor components are orthologous across plant and non-plant species, it appears that the functions of these have expanded or diverged in a lineage specific manner.

Prokaryotic community structure in photosynthetic biofilms from extreme acidic streams, Río Tinto (SW, Spain)

Four algal photosynthetic biofilms were collected from the Rio Tinto (SW Spain) at four localities: AG, Euglena and Pinnularia biofilms; ANG, Chlorella and Pinnularia biofilms; RI, Cyanidium and Dunaliella biofilms; and CEM, Cyanidium , Euglena and Pinnularia biofilms. Community composition and structure were studied by a polyphasic approach consisting of 16S rRNA analysis, scanning electron microscopy by back-scattered electron detection mode (SEM-BSE), and fluorescence in-situ hybridization (FISH). Acidophilic prokaryotes associated with algal photosynthetic biofilms included sequences related to the Alpha-, Beta-, and Gammaproteobacteria (phylum Proteobacteria) and to the phyla Nitrospira, Actinobacteria, Acidobacteria and Firmicutes. Sequences from the Archaea domain were also identified. No more than seven distinct lineages were detected in any biofilm, except for those from RI, which contained fewer groups of Bacteria . Prokaryotic communities of the thinnest algal photosynthetic biofilms ( 200 μm) generate microniches that could facilitate the development of less-adapted microorganisms (coming from the surrounding environment) to extreme conditions, thus resulting in a more diverse prokaryotic biofilm. [ Int Microbiol 2008; 11(4):251-260]

Isolation and characterization of a virus (CvV-BW1) that infects symbiotic algae of Paramecium bursaria in Lake Biwa, Japan

BackgroundWe performed an environmental study of viruses infecting the symbiotic single-celled algae of Paramecium bursaria (Paramecium bursaria Chlorella virus, PBCV) in Lake Biwa, the largest lake in Japan. The viruses detected were all Chlorella variabilis virus (CvV = NC64A virus). One of them, designated CvV-BW1, was subjected to further characterization.ResultsCvV-BW1 formed small plaques and had a linear DNA genome of 370 kb, as judged by pulsed-field gel electrophoresis. Restriction analysis indicated that CvV-BW1 DNA belongs to group H, one of the most resistant groups among CvV DNAs. Based on a phylogenetic tree constructed using the dnapol gene, CvV was classified into two clades, A and B. CvV-BW1 belonged to clade B, in contrast to all previously identified virus strains of group H that belonged to clade A.ConclusionsWe conclude that CvV-BW1 composes a distinct species within C. variabilis virus.

Sequential dark–photo fermentation and autotrophic microalgal growth for high-yield and CO 2-free biohydrogen production

Dark fermentation, photo fermentation, and autotrophic microalgae cultivation were integrated to establish a high-yield and CO 2-free biohydrogen production system by using different feedstock. Among the four carbon sources examined, sucrose was the most effective for the sequential dark (with Clostridium butyricum CGS5) and photo (with Rhodopseudomonas palutris WP3-5) fermentation process. The sequential dark–photo fermentation was stably operated for nearly 80 days, giving a maximum H 2 yield of 11.61 mol H 2/mol sucrose and a H 2 production rate of 673.93 ml/h/l. The biogas produced from the sequential dark–photo fermentation (containing ca. 40.0% CO 2) was directly fed into a microalga culture ( Chlorella vulgaris C–C) cultivated at 30 °C under 60 μmol/m 2/s illumination. The CO 2 produced from the fermentation processes was completely consumed during the autotrophic growth of C. vulgaris C–C, resulting in a microalgal biomass concentration of 1999 mg/l composed mainly of 48.0% protein, 23.0% carbohydrate and 12.3% lipid.

Chlorella variabilis and Micractinium reisseri sp. nov. (Chlorellaceae, Trebouxiophyceae): Redescription of the endosymbiotic green algae of Paramecium bursaria (Peniculia, Oligohymenophorea) in the 120th year

SUMMARY Symbiotic algae of the ciliate Paramecium bursaria (Ehrenberg) Focker are key species in the fields of virology and molecular evolutionary biology as well as in the biology of symbiotic relationships. These symbiotic algae were once identified as Zoochlorella conductrix Brandt by the Dutch microbiologist, Beijerinck 120 years ago. However, after many twists and turns, the algae are today treated as nameless organisms. Recent molecular analyses have revealed several different algal partners depending on P. bursaria strains, but nearly all P. bursaria contains a symbiont belonging to either the so-called ‘American’ or ‘European’ group. The absence of proper names for these algae is beginning to provoke ill effects in the above-mentioned study areas. In the present study, we confirmed the genetic autonomy of the ‘American’ and ‘European’ groups and described the symbionts as Chlorella variabilis Shihira et Krauss and Micractinium reisseri Hoshina, Iwataki et Imamura sp. nov., respectively (Chlorellaceae, Trebouxiophyceae).