The great biodiversity of the Serra da Bodoquena is the result of years of biological evolution. A complex combination of natural factors allows aquatic plants, fish and invertebrates to coexist in absolutely crystalline water springs. Together, organisms form an intricate web of life, connecting a single-celled microalga with large river predators. For better knowledge of the biodiversity of microalgae, an important tool is the bioprospecting and study of novel species, avoiding as much as possible the introduction of exotic species. Thus, the aim of this work was bioprospecting microalgae species from Bonito, MS, Brazil, in order to obtain more information about the local microbial biodiversity. Freshwater samples were collected from two lakes of the municipality. The samples were plated in Basic Basal medium added of bacteriological agar. After plating, the samples were kept in a biochemical oxygen demand (BOD) oven at 25ºC with photoperiod for growth. After isolation of the obtained colonies, the identification of the species was carried out according to the morphological characteristics of cells. Despite the long periods for adaptation, seven microalgae taxa were successfully isolated from the samples collected, four at the genus level and three at the species level; one from the Trebouxiophyceae class, five from the Chlorophyceae class and one from the Bacillariophyceae class.

Growth studies are important to increase the knowledge about the physiology of microalgae. The development of suitable culture media allows optimum growth to each species. The genus Chlorella has the ability to adapt to various environmental and nutritional conditions. Thus, the aim of this work was to evaluate the physiology of Chlorella sorokiniana CTT 7727 at different growth conditions with Basal Bold (BB) medium. For that, heterotrophic, autotrophic and mixotrophic cultures were carried out. The maximum specific growth rates (µ), the maximum biomass concentrations (X) and cell productivities (P) were calculated for each experiment. Among all the treatments evaluated, that with 24 h light, 3x BB (g L) and CO presented a higher µ (0.40 day) and maximum cell concentration due the increased concentration of nutrients. Replacement of dark to light has increased X from 2.3 × 10 to 9.3 × 10 cells mL in regular BB medium and 3.6 × 10 to 2.1 × 10 cells mL in 3x BB medium in autotrophic cultivations. The P increased from 2.4 × 10 cells mL h (1x BB (g L)) to 3.6 × 10 cells mL h (3x BB (g L)), in the presence of 24 light and CO. However, the same behaviour was not observed when BB concentration was increased 6, 8 or 10 times the initial concentration of BB medium. Experiments with pulses of concentrated nutrients showed that declining cells can resume their growth after nutrient depletion, but the viability is decreased after successive pulses.

The ability of microalgae to grow heterotrophically lies in the ability to oxidize organic compounds present in the external environment. The aim of this work was to evaluate the growth of Chlorella vulgaris under heterotrophic culture conditions using Basal Bold and NPK media supplemented with different sole carbon sources (glucose, fructose, sucrose, glycerol or acetate). The kinetic parameters obtained were maximum specific growth rate (μ max), doubling time (DT), maximal absorbance, which was also converted to cell concentration values using a linear relation, and cell productivity (P X). Among all the treatments analyzed, the highest maximum specific growth rate found was 0.030 hour-1 (0.72 day-1) in the treatment using Basal Bold medium supplemented with glucose. The highest cellular concentration and cell productivity were also found for this same treatment (4.03 x 10 6 cell mL-1 and 64.0 x 10 6 cell L-1 day-1 , respectively). It was concluded that that the Basal Bold medium was more efficient for Chlorella vulgaris growth, since it induced higher values of μ max and cellular concentration. Results obtained were very reproducible using microplate assay.