Improving biomass and carbohydrate production of microalgae in the rotating cultivation system on natural carriers.

Biofilm-based algal technologies have gained popularity due to higher biomass productivity, efficient harvesting, and water-saving over suspended growth systems. A rotating attached system was designed to assess the biofilm-forming capacity of different isolated microalgal strains from the Persian Gulf. Four microalgal strains, including two Chlorella sp., one Picochlorum sp. and one filamentous cyanobacterium Desmonostoc sp. were cultivated on four carriers: jute, cotton, yarn and nylon. The carriers' physicochemical surface characteristics and attachment effects, like contact angle, were investigated. The incorporated biomass and exopolysaccharides (EPS) content in the suspended and biofilm system was calculated and compared. The results showed that the cyanobacterium strain had the biofilm formation capability on both jute and cotton in the attached cultivation system. Under the same culture conditions, the biomass productivity on jute and cotton carriers was significantly higher (4.76 and 3.61 g m- 2 respectively) than the growth in aqueous suspension (1.19 g m- 2 d- 1). The greatest incorporated exopolysaccharides amount was observed on jute (43.62 ± 4.47%) and the lowest amount was obtained from the growth on positive charge yarn (18.62 ± 1.88%). This study showed that in comparison with planktonic growth, the colonization of cyanobacterial cells and subsequent production of extracellular matrix and biofilm formation can lead to increased biomass production.

Characterization, antioxidant and anticoagulant properties of exopolysaccharide from marine microalgae.

The sulfated exopolysaccharide extracted from marine microalgae attracted considerable attention from both the nutraceutical and pharmaceutical industries. In the present study biomass of five marine microalgae were screened to find strains with high capacity for the production of sulfated exopolysaccharides. The anticoagulant and antioxidant activities of extracted sulfated polysaccharides were evaluated using activated partial thromboplastin time (aPTT), prothrombin time (PT), DPPH and ABTS assays, respectively. The sulfated polysaccharides extracted from Picochlorum sp. showed a strong DPPH scavenging effect with 85% antioxidant activity. The sulfated polysaccharides of Chlorella sorokiniana, Chlorella sp. (L2) and Chlorella sp. (D1) scavenged more than 90% of the ABTS radicals. However, the sulfated polysaccharide extracted from Chlorella sorokiniana, and Chlorella sp. (N4) showed anticoagulant properties. The dual anticoagulant-antioxidant activities in Chlorella sorokiniana could be explained by the combination of various factors including sulfate content and their binding site, monosaccharide residue and glycoside bond which are involved in the polysaccharide's bioactivity.

Protective Effects of Cryoprotectants and Lyoprotectants on the Survival of Persipeptide Producing Streptomyces zagrosensis UTMC 1154.

Streptomyces sp. are bacteria recognized as the producers of more than half of the known bioactive compounds. Developing appropriate preservation methods for industrial strains of Streptomyces is necessary, as continuous subculture could have significant negative effects on their characteristics, including their potential to produce secondary metabolites. The effects of two common preservation methods on a bioactive metabolite producer, Streptomyces zagrosensis UTMC 1154, were studied. In the cryopreservation method, glycerol and dimethyl sulfoxide (DMSO) were evaluated as cryoprotectants. Three different suspending fluids including skimmed milk, sucrose+gelatin and Mist. dessicans were compared as the freeze-drying methods. Freeze-dried samples were stored at 4°C for 6 months and at 37°C for 1 and 2 weeks in an accelerated storage stability study, which approximately correspond to storage at 4°C for 10 and 20 years, respectively. Frozen samples were stored at -20°C, -70°C and in the vapor phase of liquid nitrogen for 6 months. Skimmed milk and DMSO were the most efficient protectants for survival and functional maintenance of the strain during the lyophilization and cryopreservation processes (p < 0.05), respectively. The survival rate of S. zagrosensis was 95.0% and 99.3% after 6 months of preservation by using skimmed milk as lyoprotectant and DMSO as the cryoprotectant, respectively. The obtained results showed that cryopreservation is the method of choice for long-term preservation of S. zagrosensis. Cryopreservation also led to only 1%-3% reduction in the biological activity of the strain after 6 months preservation in vapor phase of the liquid nitrogen.