Effects of Sodium Nitrate and Mixotrophic Culture on Biomass and Lipid Production in Hypersaline Microalgae Dunaliella Viridis Teod

To access the potential application of Dunaliella viridis Teod. for biofuel production, the effects of culture media composition on biomass and lipid content of this microalgae were investigated. Measured at the 20 th day, sodium nitrate at 5.0 mM augmented biomass production by 26.5 percent compared to control (1 mM sodium nitrate). Total lipids expressed as µg mL-1 of culture also increased with increase in nitrate concentration up to 5.0 mM sodium nitrate, whereas when expressed on the per cell basis, total lipids stayed relatively constant at most of the tested nitrate concentrations except at 0.5 mM which was 31.4 percent higher compared to 1.0 mM nitrate. At 5.0 mM sodium nitrate, by using 20 g L-1 of glucose in mixotrophic culture of D. viridis, cell number augmented by 36.4 percent compared to the cultures with no added glucose. Llipid content per cell and per mL of culture was increased by 71.4 and 135.1 percent, respectively. Among plant hormones, 10-9 M indole-3- acetic acid (IAA) plus 10 -8 M trans-zeatin riboside led to 22.8 percent higher biomass relative to control (without hormone and at 1.0 mM sodium nitrate). It is concluded that altering the growth conditions of D. viridis can lead to higher cell densities and higher lipids content which can be exploited for biofuel production.

Cultivo da microalga spirulina platensis em fontes alternativas de nutrientes / Culture of microalga Spirulina platensis in alternative sources of nutrients

O Brasil gera cerca de 18 milhões de toneladas de melaço por ano, com aproximadamente 50 por cento de açúcares e carece de maior quantidade de alimentos que auxiliem no combate à desnutrição. Spirulina platensis é uma microalga que pode conter 74 por cento de proteínas e, embora seja um microrganismo autotrófico, a complementação do meio de cultivo com carbono orgânico pode estimular seu crescimento. S. platensis foi cultivada em modo autotrófico com bicarbonato de sódio, e mixotrófico com 0,25; 0,50; 0,75 e 1,00 g.L-1 de melaço em pó (MEP) ou melaço líquido (MEL). A presença de MEL ou MEP resultou em crescimento por, no mínimo 35 dias, e melhores parâmetros de crescimento que os cultivos autotróficos que cresceram durante 30 dias. Utilizando ME P 0,25 g.L-1 a maior concentração de biomassa foi 2,59 g.L-1 e produtividade 0,066 g.L-1.dia-1, enquanto cultivos autotróficos alcançaram 1,44 g.L-1 e 0,045 g.L-1.dia-1. A máxima concentração de biomassa (2,83 g.L-1) e produtividade (0,098 g.L-1.dia-1) foram obtidas em MEL 0,50 g.L-1. Os resultados demonstram que o potencial brasileiro de produção de melaço pode ser explorado também para obtenção de altas concentrações de biomassa no cultivo da microalga Spirulina platensis.

Brazil produces approximately 18,000,000 tons of molasses per year, containing 50 percent of sugars. This country needs more food help for the malnourishment disease. Spirulina platensis is a microalga that contains up to 74 percent proteins. It grows photoautotrophically, but the medium complementation with organic carbon may stimulate its growth. S. platensis was grown autotrophically and mixotrofically with 0.25; 0.50; 0.75 and 1.00 g.L-1 of powder molasses (MEP) or liquid molasses (MEL). Cultures with MEL or MEP have grown for more long time (minimum 35 days) and have reached higher biomass concentration and productivity than autotrophic one, that grew during 30 days. Cultures with MEP 0.25 g.L-1 have reached biomass concentration of 2.59 g.L-1 and productivity of 0.066 g.L-1.day-1. Maximum biomass concentration (2.83 g.L-1) and productivity (0.098 g.L-1.day-1-) were reached in cultures with MEL 0.50 g.L-1. Autotrophic cultures reached 1.44 g.L-1 and 0.045 g.L-1.day-1. Results showed that the Brazilian potential of molasses production may be also exploited to obtain higher biomass concentration in the culture of microalga Spirulina platensis.