Unstructural studies of microalgae

Abstract

The optimization of fixation protocols was undertaken for Dunaliella salina, Nannochloropsis oculata and Pseudostaurosira trainorii to investigate two different aspects of microalgal biology. The first was to evaluate the effects of the infochemical 2, 4-decadienal as a potential lipid inducer in two promising lipid-producing species, Dunaliella salina and Nannochloropsis oculata, for biofuel production. D. salina fixed well using 1% glutaraldehyde in 0.5 M cacodylate buffer prepared in F/2 medium followed by secondary fixation with 1% osmium tetroxide. N. oculata fixed better with combined osmium-glutaraldehyde prepared in sea water and sucrose. A stereological measuring technique was used to compare lipid volume fractions in D. salina cells treated with 0, 2.5, and 50 μM and N. oculata treated with 0, 1, 10, and 50 μM with the lipid volume fraction of naturally senescent (stationary) cultures. There were significant increases in the volume fractions of lipid bodies in both D. salina (0.72%) and N. oculata (3.4%) decadienal-treated cells. However, the volume fractions of lipid bodies of the stationary phase cells were 7.1% for D. salina and 28% for N. oculata. Therefore, decadienal would not be a suitable lipid inducer for a cost-effective biofuel plant. Moreover, cells treated with the highest concentration of decadienal showed signs of programmed cell death. This would affect biomass accumulation in the biofuel plant, thus further reducing cost effectiveness. The second investigation used the cell structure and gametogenesis of Pseudostaurosira trainorii to evaluate the cytoplasmic support for the molecular phylogeny of diatoms proposed by Medlin and Kaczmarska (2004) which divides diatoms into three clades that differ in their ultrastructure, where Clade 1 contains centric diatoms, Clade 2a centric bipolar and multipolar diatoms and Clade 2b pennate diatoms. P. trainorii is classified as araphid diatom which has a thread-like structure reported by Sato et al. (2011) that could resemble the flagella in centric diatoms. P. trainorii fixed better with combined osmium-glutaraldehyde prepared in sea water and sucrose, and it was found that its Golgi apparatus and auxospore were resemble those of Clade 2b, while the pyrenoid structure might represent a variation of the structures described for other members of Clade 2b. In addition, this study proved that the thread-like structures in P. trainorii were not flagella.