The effect of hydrodynamic stress derived from gas bubble dispersion and broth mixing on Dunaliella growth was examined by growing the algae in two different vessels; a Roux bottle and a miniloop reactor. It was found that Dunaliella cells were increasingly sensitive to high specific bubble rates at modified orifice Reynolds numbers between 9 . 9~1 P to 18-8XlP and liquid motion with Reynolds numbers between 712 and 1293. The addition of carboxymethylcellulose and agar to the cultures served to protect the microorganisms from the effects of shear stress.

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.

Chlorella cultures were grown in a tubular loop reactor which facilitated both irradiation of the culture and gas mixing compared with a conventional stirred vessel with vortex aeration. Measurements of the inhibition of maximum specific growth rate (proportional to photosynthetic rate) in the tubular reactor showed that C02 behaves as a typical inhibitory substrate at partial pressures (Pco,) up to 0.6 atm. The Pco, for 50% reduction in maximum specific growth rate was 0.36 atm. At 0 4 atm there was a discontinuity in the inhibitory effect with a sharp increase in the inhibitory effect at higher Pco, values. Cultures rapidly adjusted to step changes in the Pco, up to 0.6 atm. At a Pco2 of 1 atm inhibition was complete but the inhibitory effect was readily reversed.

The effect of nutritional factors in a new culture medium (BW3) is described for the cyanobacterium Nostoc sp. The growth of Nostoc sp. was higher in BW3 than in control media currently used for cyanobacteria. With medium BW3 the content of the pigment c-phycocyanin depended on the culture conditions employed, particularly the nature of the nitrogen and carbon sources. Higher amounts of c-phycocyanin amounting to 20.1% on a dry-weight basis were accumulated when both sources were supplied in the gas phase of the culture. The phycobiliproteins of Nostoc sp. were resolved into two components: c-phycocyanin (2max=614nm) and allophycocyanin (2max =652 rim). The phycobiliprotein composition was 30% allophycocyanin and 70% c-phycocyanin. The culture of Nostoc sp. in BW3 medium seems promising as a source of biomass for the production of natural dyes.