| Botryococcus braunii is considered as an energy microalgae having great protential applications because of that it can synthesize and accumulate considerable quantities of hydrocarbons in the metabolic process. The calorific value, composition and structure of these hydrocarbons are very similar to those of oil. Generally the content of total hydrocarbons could reach 25% to 40% of dry biomass and the maximum value that have reported was 76%.The microscopic structure and sub-microscopic structure of three B. braunii strains (AGB-Bb01,AGB-Bb02 and AGB-Bb03) isolated from different sites were observed by light and electronic microscope observations based on morphological features. AGB-Bb01, AGB-Bb02 and AGB-Bb03 were identified as different genotype and geographical strains of B. braunii by amplifying the 18S-28S rDNA and rbcL gene sequences and blastn analysis, genetic distance and sequence similarities calculation. And it is the first time that the rbcL gene sequences were obtained from this energy microalgae. The phylogenetic trees involved in 16 strains of B. braunii were reconstructed based on the genetic distances and sequence similarities of 18S rDNA, ITS region and rbcL gene sequences at the same time. The results showed that the cell size, colony size and cell number in one colony of the three geographical strains were significantly different. The sub-microscopic structures demonstrated that the thickness of the cup-sheath and extent of cell embedded by the cup-sheath had difference among the three strains as well. There existed high genetic diversity among the different strains living in the different sites and phylogenetic tree showed that all the strains can be divided into 2 groups and 4 sub-groups because of the geographical isolation. It is proved that sequences of 18S rDNA and ITS region can be considered as good tools for gene-type identification and genetic diversity research in B. braunii. Phylogenetic trees were constructed using Neighbor-joining, Minimum evolution, Maximum parsimony and Unweighted pair-group method with arithmetic method, and their reliability was estimated using bootstrap analysis. All the results show the closest relatives are in the Chlamydomonadales with high bootstrap. The study lays the solid basement for the research of the genetic diversity and cultivation in B. braunii.It is very necessary to breed algae strains and optimize culture conditions in order to achieve large-scale production. The preferred target is to obtain high-yield varieties which can both grow rapidly and have high content of total hydrocarbons and total lipids. Total hydrocarbons and total lipids of B. braunii AGB-Bb01, AGB-Bb02 and AGB-Bb03 was different in different growth phases. The maximum of those appeared in the post-logarithmic phase after algae cells in the lag phase, the early-logarithmic phase, the post-logarithmic phase and the stationary phase were collected and fragmented for determination. The effect of the media on the growth, contents of total hydrocarbons and total lipids of Botryococcus braunii AGB-Bb01, AGB-Bb02 and AGB-Bb03 was studied using different media such as modified Chu10 medium, modified Chul3 medium,BGll and bold basal medium(BBM). Biomass of B. braunii AGB-Bb01 cultured in Chu13 was higher than that cultured in Chu10, BG11 and BBM, while biomass of B. braunii AGB-Bb02 and AGB-Bb03 cultured in BG11 were higher than those cultured in the other medium respectively;Chu10 was found to be the best medium for total hydrocarbon content and total lipid content of B. braunii AGB-Bb01 and AGB-Bb02, whereas Chul3 is the best for total hydrocarbon content and total lipid content of B. braunii AGB-Bb03. This research provides experimental basis for the selection of the best harvest time and industrial large-scale production of B. braunii.
|
PDF Full Text Request