Enzymatic antioxidant response to low-temperature acclimation in the cyanobacterium Arthrospira platensis

Changes in antioxidant enzyme activities in response to low-temperature-induced photoinhibition were investigated in the two strains of the cyanobacterium Arthrospira platensis, Kenya and M2. When transferred to 15 degrees C from 33 degrees C, cells exhibited an immediate cessation of growth followed by a new acclimated growth rate. Although both strains had similar growth rates at 33 degrees C, once transferred to a lower temperature environment, Kenya had a faster growth rate than M2. There were variations in the antioxidant enzyme activities of both strains during 15 degrees C acclimation. The activity of superoxide dismutase from Kenya was higher than that from M2 and increased remarkably with acclimation time. Catalase activity of both strains increased at first but decreased later in the acclimation process. Ascorbate-dependent peroxidase activity of the Kenya strain declined when transferred to the low-temperature environment while peroxidase activity of M2 decreased in the beginning and then increased with time. The dehydroascorbate reductase activity of both strains was variable during the acclimation period while the glutathione reductase activity was not modified immediately. Our finding may support that the faster growth rate of the Kenya strain at lower temperatures as compared with the M2 strain might be explained by the higher antioxidant enzyme activities of Kenya at lower temperatures and through its ability to apply a more efficient regulatory strategy of enzymatic antioxidant response to low-temperature-induced photoinhibition

Photosynthetic characterization of two Nannochloropsis species and its relevance to outdoor cultivation

Despite the increased interest in exploring the potential of algal biomass production for food stock and renewable energy, very little work has been done in developing reliable screening protocols to enable the identification of species that are best suited to mass cultivation outdoors. Nannochloropsis is an algal genus identified as a potential source of lipids due to its ability to accumulate large quantities of these compounds, especially under nutrient-limiting conditions. The objective of the current work was to use two species of this genus, Nannochloropsis oceanica and N. oculata, as model organisms to develop a protocol that will allow the evaluation of their capacity to yield high biomass productivity under outdoor conditions. Growing the alga under different light intensities and measuring growth rate as well as a range of photosynthetic parameters based on light response curves and variable fluorescence highlighted significant differences between the two species. Our data show that N. oceanica cells have a better capacity to respond to higher light intensities, as reflected by growth measurements, photosynthetic electron transport rates, and oxygen evolution as well as their response to the very high photon flux densities expected in outdoor culture. On the other hand, N. oculata showed a higher tolerance to oxidative stress as reflected in its resistance to the reactive oxygen species generating compounds Rose Bengal (RB) and methyl viologen (MV). Based on the above evidence, we suggest that N. oceanica may perform better than N. oculata when grown under high light conditions typically found outdoors in summer, while N. oculata may perform better than N. oceanica under oxidative stress conditions usually found in outdoor cultures exposed to a combination of high light and low temperature commonly occurring in winter time.European Commission/[727874]/EU/Unión EuropeaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR