Introduction of a novel 18S rDNA gene arrangement along with distinct ITS region in the saline water microalga Dunaliella

Biochemical profiling of three indigenous Dunaliella isolates with main focus on fatty acid composition towards potential biotechnological application

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Biochemical composition of native isolates determined their potential application.

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The isolates tend to store energy and carbon mainly in lipid, not carbohydrate, form.

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The fatty acid profile of the isolates show appropriate n3:n6 and health lipid indices.

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Dunaliella sp. ABRIINW-B1 and -G2/1 are the proper options for nutraceutical purposes.

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Dunaliella sp. ABRIINW-I1 well suits pharmaceutical and aquaculture application.

This study describes the biochemical composition of three isolates, Dunaliella sp. ABRIINW-B1, -G2/1 and -I1 towards the biotechnological potential. Dunaliella sp. ABRIINW- G2/1 and -I1 had a remarkable protein content (∼40% dry weight). Dunaliella sp. ABRIINW-I1 contained a pigment fraction of 3.2% largely composed of chlorophyll a (1.9%) and carotenoid (1.1%). Dunaliella sp. ABRIINW-B1, -G2/1 and -I1 produced respectively 42, 36 and 47% lipid content. The occurrence of high lipid and low carbohydrate (4–7%) in the isolates demonstrated their cell tendency to store energy and carbon mainly in lipid form. The lipid profile of the isolates expressed adequate n3:n6 ratio and health indices. The biochemical analysis revealed that Dunaliella sp. ABRIINW-B1 and -G2/1 have potential applications in the food and freshwater aquafeed sector. While Dunaliella sp. ABRIINW-I1 owing to appropriate pigment, protein, and lipid level containing very-long-chain polyunsaturated fatty acids showed a great promise in nutritional, pharmaceutical and marine aquafeed industries.

Phylogenetic analysis of Dunaliella (Chlorophyta) emphasizing new benthic and supralittoral isolates from Great Salt Lake

Dunaliella, a commercially important chlorophyte, is globally distributed in saline habitats. Morphological species have not been definitively reconciled with phylogenetic analyses. Considerable genetic diversity continues to be discovered in new isolates, especially from soil and benthic habitats. Twenty-nine new isolates from Great Salt Lake, Utah, many from benthic or supralittoral habitats, were phylogenetically analyzed using ITS1+5.8S+ITS2 in comparison to a broad sampling of available sequences. A few new isolates align in one branch of a bifurcated monophyletic Dunaliella salina clade and several cluster within monophyletic D. viridis. Several others align with relatively few unnamed strains from other locations, comprising a diverse clade that may represent two or more new species. The overall Dunaliella clade is relatively robust, but the nearest outgroups are ambiguously placed with extremely long branches. About half of the isolates, all from benthic or supralittoral habitats, have been persistently sarcinoid in liquid media since isolation. This trait is spread across the Dunaliella phylogeny. The morphology of two sarcinoid strains was documented with light microscopy, revealing an extensive glycocalyx. Clumping behavior of unicellular and sarcinoid strains was unaffected by presence or absence of Mg²⁺ or Ca²⁺ , addition of lectin-inhibiting monosaccharides, or water-soluble factors from morphologically opposite strains. Results from this investigation have significantly expanded our current understanding of Dunaliella diversity, but it seems likely that much remains to be discovered with additional sampling.

A simple and inexpensive physical lysis method for DNA and RNA extraction from freshwater microalgae

In this work, a simple and inexpensive physical lysis method using a cordless drill fitted with a plastic pellet pestle and 150 mg of sterile sea sand was established for the extraction of DNA from six strains of freshwater microalgae. This lysis method was also tested for RNA extraction from two microalgal strains. Lysis duration between 15 and 120 s using the cetyltrimethyl ammonium bromide (CTAB) buffer significantly increased the yield of DNA from four microalgalstrains (Monoraphidium griffithii NS16, Scenedesmus sp. NS6, Scenedesmus sp. DPBC1 and Acutodesmus sp. DPBB10) compared to control. It was also found that grinding was not required to obtain DNA from two strains of microalgae (Choricystis sp. NPA14 and Chlamydomonas sp. BM3). The average DNA yield obtained using this lysis method was between 62.5 and 78.9 ng/mg for M. griffithii NS16, 42.2-247.0 ng/mg for Scenedesmus sp. NS6, 70.2-110.9 ng/mg for Scenedesmus sp. DPBC1 and 142.8-164.8 ng/mg for Acutodesmus sp. DPBB10. DNA obtained using this method was sufficiently pure for PCR amplification. Extraction of total RNA from M. griffithii NS16 and Mychonastes sp. NPD7 using this lysis method yielded high-quality RNA suitable for RT-PCR. This lysis method is simple, cheap and would enable rapid nucleic acid extraction from freshwater microalgae without requiring costly materials and equipment such as liquid nitrogen or beadbeaters, and would facilitate molecular studies on microalgae in general.

Efficient and stable transformation of Dunaliella pseudosalina by 3 strains of Agrobacterium tumefaciens

Introduction: Several platforms including mammalian, plant and insect cells as well as bacteria, yeasts, and microalgae are available for the production of recombinant proteins. Low efficiency of delivery systems, extracellular and intracellular degradation of foreign genes during transformation, difficulties in targeting and importing into the nucleus, and finally problems in integration into nuclear genome are the most bottlenecks of classical plasmids for producing recombinant proteins. Owing to high growth rate, no common pathogen with humans, being utilized as humans’ food, and capability to perform N-glycosylation, microalgae are proposed as an ideal system for such biotechnological approaches. Here, Agrobacterium tumefaciens is introduced as an alternative tool for transformation of the microalga Dunaliella pseudosalina.

Methods: The transformation of gfp gene into the D. pseudosalina was evaluated by three strains including EHA101, GV3301 and GV3850 of A. tumefaciens. The integrating and expression of gfp gene were determined by PCR, RT-PCR, Q-PCR and SDS-PAGE analyses.

Results: The T-DNA of pCAMBIA1304 plasmid was successfully integrated into the genome of the microalgal cells. Although all of the strains were able to transform the algal cells, GV3301 possessed higher potential to transform the microalgal cells in comparison to EHA101 and GV3850 strains. Moreover, the stability of gfp gene was successfully established during a course of two months period in the microalgal genome.

Conclusion : Agrobacterium is introduced as a competent system for stable transformation of Dunaliella strains in order to produce eukaryotic recombinant proteins.

Biochemical Modulation of Lipid Pathway in Microalgae Dunaliella sp. for Biodiesel Production

Exploitation of renewable sources of energy such as algal biodiesel could turn energy supplies problem around. Studies on a locally isolated strain of Dunaliella sp. showed that the mean lipid content in cultures enriched by 200 mg L(-1) myoinositol was raised by around 33% (1.5 times higher than the control). Similarly, higher lipid productivity values were achieved in cultures treated by 100 and 200 mg L(-1) myoinositol. Fluorometry analyses (microplate fluorescence and flow cytometry) revealed increased oil accumulation in the Nile red-stained algal samples. Moreover, it was predicted that biodiesel produced from myoinositol-treated cells possessed improved oxidative stability, cetane number, and cloud point values. From the genomic point of view, real-time analyses revealed that myoinositol negatively influenced transcript abundance of AccD gene (one of the key genes involved in lipid production pathway) due to feedback inhibition and that its positive effect must have been exerted through other genes. The findings of the current research are not to interprete that myoinositol supplementation could answer all the challenges faced in microalgal biodiesel production but instead to show that "there is a there there" for biochemical modulation strategies, which we achieved, increased algal oil quantity and enhanced resultant biodiesel quality.

The ecology of Dunaliella in high-salt environments

Halophilic representatives of the genus Dunaliella, notably D. salina and D. viridis, are found worldwide in salt lakes and saltern evaporation and crystallizer ponds at salt concentrations up to NaCl saturation. Thanks to the biotechnological exploitation of D. salina for β-carotene production we have a profound knowledge of the physiology and biochemistry of the alga. However, relatively little is known about the ecology of the members of the genus Dunaliella in hypersaline environments, in spite of the fact that Dunaliella is often the main or even the sole primary producer present, so that the entire ecosystem depends on carbon fixed by this alga. This review paper summarizes our knowledge about the occurrence and the activities of different Dunaliella species in natural salt lakes (Great Salt Lake, the Dead Sea and others), in saltern ponds and in other salty habitats where members of the genus have been found.

Hemato-immunological responses of Heros severus fed diets supplemented with different levels of Dunaliella salina

In this study, the effects of oral administration of different levels of Dunaliella salina (a natural β-carotene source) on growth parameters, immunological and hematological indices, as well as skin carotenoids, of Heros severus were investigated. One hundred and eighty H. severus weighing 27 ± 0.5 g were divided randomly into four groups in triplicate (15 fish in each replicate). Groups 1-4 received food supplemented with 0, 50, 100 and 200 mg kg⁻¹ D. salina powder, respectively. After 6 weeks, the growth parameters were compared among the groups. Blood samples were taken from each group, and hematological parameters including red blood cell count (RBC), white blood cell count (WBC), hematocrit (PCV), hemoglobin (Hb) and immunological indices (serum and mucus lysozyme and bactericidal activity, resistance against Aeromonas hydrophila infection) as well as carotenoid content of skin were evaluated. Results showed that some growth indices increased significantly in fish fed with 100 and 200 mg kg⁻¹ D. salina-supplemented food (P < 0.05). Although serum lysozyme activity was increased in fish fed with food supplemented with 100 and 200 mg kg⁻¹ D. salina (P < 0.05), no significant change was observed in serum and mucus bactericidal activity and mucus lysozyme activity among the groups (P > 0.05). Most of the hematological parameters such as WBC, RBC, PCV and Hb significantly increased in D. salina-treated fish compared with controls (P < 0.05). Mortality induced after challenge with A. hydrophila in 200 mg kg⁻¹ D. salina-treated fish was 36.67 %, which significantly decreased compared with control (P < 0.05). Skin carotenoid content in all D. salina treatments was statistically higher than that of control (P < 0.05). Conclusively, D. salina as a food additive can affect positively the growth, immunological and hematological parameters of H. severus.

Characterization of eukaryotic microbial diversity in hypersaline Lake Tyrrell, Australia

This study describes the community structure of the microbial eukaryotic community from hypersaline Lake Tyrrell, Australia, using near full length 18S rRNA sequences. Water samples were taken in both summer and winter over a 4-year period. The extent of eukaryotic diversity detected was low, with only 35 unique phylotypes using a 97% sequence similarity threshold. The water samples were dominated (91%) by a novel cluster of the Alveolate, Apicomplexa Colpodella spp., most closely related to C. edax. The Chlorophyte, Dunaliella spp. accounted for less than 35% of water column samples. However, the eukaryotic community entrained in a salt crust sample was vastly different and was dominated (83%) by the Dunaliella spp. The patterns described here represent the first observation of microbial eukaryotic dynamics in this system and provide a multiyear comparison of community composition by season. The lack of expected seasonal distribution in eukaryotic communities paired with abundant nanoflagellates suggests that grazing may significantly structure microbial eukaryotic communities in this system.

Phenotypic and genetic characterization of Dunaliella (Chlorophyta) from Indian salinas and their diversity

BACKGROUND

The genus Dunaliella (Class - Chlorophyceae) is widely studied for its tolerance to extreme habitat conditions, physiological aspects and many biotechnological applications, such as a source of carotenoids and many other bioactive compounds. Biochemical and molecular characterization is very much essential to fully explore the properties and possibilities of the new isolates of Dunaliella. In India, hyper saline lakes and salt pans were reported to bloom with Dunaliella spp. However, except for the economically important D. salina, other species are rarely characterized taxonomically from India. Present study was conducted to describe Dunaliella strains from Indian salinas using a combined morphological, physiological and molecular approach with an aim to have a better understanding on the taxonomy and diversity of this genus from India.

RESULTS

Comparative phenotypic and genetic studies revealed high level of diversity within the Indian Dunaliella isolates. Species level identification using morphological characteristics clearly delineated two strains of D. salina with considerable β-carotene content (>20 pg/cell). The variation in 18S rRNA gene size, amplified with MA1-MA2 primers, ranged between ~1800 and ~2650 base pairs, and together with the phylogeny based on ITS gene sequence provided a pattern, forming five different groups within Indian Dunaliella isolates. Superficial congruency was observed between ITS and rbcL gene phylogenetic trees with consistent formation of major clades separating Indian isolates into two distinct clusters, one with D. salina and allied strains, and another one with D. viridis and allied strains. Further in both the trees, few isolates showed high level of genetic divergence than reported previously for Dunaliella spp. This indicates the scope of more numbers of clearly defined/unidentified species/sub-species within Indian Dunaliella isolates.

CONCLUSION

Present work illustrates Indian Dunaliella strains phenotypically and genetically, and confirms the presence of not less than five different species (or sub-species) in Indian saline waters, including D. salina and D. viridis. The study emphasizes the need for a combined morphological, physiological and molecular approach in the taxonomic studies of Dunaliella.