The arsenic content of various water bodies in Argentina is higher than the acceptable levels for human and animal uses. Cyanobacteria are widely distributed in aquatic environments and can bioaccumulate arsenic (As). This study presents the response of indigenous cyanobacteria to As(III) and As(V), including the species Tolypothrix tenuis, Nostoc muscorum and Nostoc minutum, previously used with biotechnological purposes. As(III) resulted more toxic than As(V) in all cases, causing cell death in the range of 5-20 mg/l. T. tenuis growth was sensitive to As(V) with lethal inhibition at 625 mg/l, whereas the Noctoc species were stimulated. EC50 values found were 73.34 mg/l for N. muscorum and 989.3 mg/l for N. minutum. Batch cultures of N. minutum showed improvements in both growth parameters and photosynthetic pigment content in the presence of 1,000 mg/l As(V). Increases of 66.7%, 75.5%, 40% and 20.7% in cell productivity, chlorophyll a, total carotenoids and C-phycocyanin respectively were observed, reaching a bioaccumulated arsenic value of 37.4 ¼g/g at the stationary growth phase.
The suitability of the cyanobacterium Tolypothrix tenuis as a potential biofertilizer was evaluated by measuring cell viability in stored samples preserved by various methods, including freezing at −20°C, freeze-drying, desiccation as flakes and immobilization in alginate beads. The viability recovery and the retained viability index (RVI 10 ) were used as indicators of cell survival after 3 and 15 months storage. The highest recovery level (85%) was obtained by freeze-drying using skimmed milk as the resuspension solution for long-term storage. Dried alginate beads showed a better cell survival (RVI 10 0.25) than air-dried flakes (RVI 10 −0.63) after 15 months storage. However, desiccated flakes previously treated with Ca 2+ and Mg 2+ ions improved cell survival capacity at the longest period assayed (RVI 10 0.08), extending cell viability by 9 months compared to dried-powder material.
The biomass production of a cyanobacterium (Nostoc sp.) in a photoreactor with a low illuminated surface area to volume ratio was improved by the reutilization of the culture medium.After six succesive utilizations the growth of Nostocsp. amounted to 2.15 g/1 with an average content in phycobiliproteins of 14.4 % on dry weight basis. The procedure reported allowed an 80 % increase in biomass. The cellular self-sedimentation proved to be effective for biomass separation between reutilization steps.
A study of the influence of different laboratory growth conditions on the biomass and EPS production by Nostoc minutum, a diazothophic cyanobacterium locally isolated, was carried out. Two culture media were tested, with or without NaNO3 addition, and three luminous intensities: low (4530 lux), intermediate (7300 lux) and high (9860 lux). BW3 medium was better than BG11 for N. minutum growth, with maximal values of biomass concentration (4.98 DO) and the highest growth rate (0.019 h −1 ) at 9860 lux of light intensity. A progressive increase in culture viscosity of N. minutum cultures was observed, for stirred condition and non-diazotrophic growth in BG11 medium, together with the production of maximal EPS concentration (2.485 g/L). On the other hand, the EPS production in BW3 medium was maximal in diazotrophic conditions, both for still (1.66 g/L) and stirred (2.56 g/L) cultures. The different yields of EPS reported for each condition, results in the requirement of a species-specific optimization of the cultivation conditions for the exploitation of an efficient technology for the production of N. minutum EPS.
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