Elucidation and isolation of specific bioactive compound in cyanobacteria isolates.

Abstract

Sulfoquinovosyldiacylglyceride (SQDG), one of the bioactive compounds isolated from Spirulina, has been proven to act as an inhibitor of reverse-transcriptase, and has potential for the use in the Combination Anti-Retroviral Therapy (cART). A number of researchers report that the many potential uses of Spirulina, with the most widely used strains being Spirulina platensis and S. maxima, require further investigation to determine their actual usefulness in medical applications. In this work, four commercial isolates marketed as Spirulina and an Australian isolate, Spirulina sp. CS-785/01 (CSIRO), were selected to determine their bio-composition and applicability as a source of bioactive compounds. During the course of the investigation, it was determined that the four commercial isolates were in fact Arthrospira and the Australian isolate is Halospirulina. However, this insight occurred towards the end of the study and the ‘Spirulina’ has been adopted as common name when referring to the isolates during the experimental programme that has been reported in the thesis. The commercial isolates used in this research were Spirulina (J), Spirulina (M), Spirulina (P) and Spirulina (S), while the Australian isolate Spirulina sp. was also used throughout the investigation. The identification of these isolates was examined based on their molecular and the chemotaxonomic classification. Furthermore, the genes responsible for the production of SQDG were isolated to assess the potential therapeutic value of these isolates in treating disease, such as HIV (Human immunodeficiency virus). Since SQDG is a compound of current interest, a suitable extraction technique was developed to optimise its production. Different extraction techniques, such as microwave-assisted sonication and homogenisation, coupled with various forms of organic solvents, were examined in this study. Preliminary phytochemical analysis was also undertaken to reveal the potential use of the investigated isolates for the further development of pharmaceuticals due to the presence of specific phyto-constituents. Finally, sequential extracts and the isolated compound of SQDG were used to determine their bioactivity against a range of microbes and HIV. The results revealed that the Australian isolate was not highly productive in respect to growth. This is due to its limited adaptability to changes in temperature and culture media type. The Australian isolate is limited to a specific temperature range and culture media type. Additionally, it has substantial biochemical variation compared to the commercial isolates. The diversity of these isolates could be explained by their molecular and chemotaxonomic classification, which revealed that the Australian isolate belongs to the genus of Halospirulina, while the commercial isolates belong to the genus Arthrospira. The carbohydrate, protein, lipid and fatty acid content of the commercial isolates also indicated that they have higher nutritional value when compared to the Spirulina sp. This strongly suggested that the commercial isolates belonged to a different genus to the Spirulina sp. In spite of the diversity of the classification, all investigated isolates showed the presence of SQDG. Overall, the results showed that Spirulina (S) has a high potential for synthesis of SQDG, due to its high content of C16:0 and C18:2, while the SQDG content of Australian isolate was lowest among the investigated isolates. By applying this data, the Australia isolate is unlikely to be suitable for large-scale production. It also showed lower appreciable amounts of SQDG and gamma linolenic acid (GLA). The highest yield of SQDG from Spirulina (M) was from using a chloroform:methanol (2:1, v/v) extraction solvent system. However, a methanol extraction solvent system is suggested, due to its high recovery of SQDG and low toxicity. Because SQDG is a potent inhibitor of HIV-reverse transcriptase, it can be concluded that commercial isolates are good sources for drug production because of their high content of SQDG and rapid biomass production.