Role of Sulfate Transporters in Chromium Tolerance in Scenedesmus acutus M. (Sphaeropleales)

Sulfur (S) is essential for the synthesis of important defense compounds and in the scavenging potential of oxidative stress, conferring increased capacity to cope with biotic and abiotic stresses. Chromate can induce a sort of S-starvation by competing for uptake with SO42− and causing a depletion of cellular reduced compounds, thus emphasizing the role of S-transporters in heavy-metal tolerance. In this work we analyzed the sulfate transporter system in the freshwater green algae Scenedesmus acutus, that proved to possess both H+/SO42− (SULTRs) and Na+/SO42− (SLTs) plasma membrane sulfate transporters and a chloroplast-envelope localized ABC-type holocomplex. We discuss the sulfate uptake system of S. acutus in comparison with other taxa, enlightening differences among the clade Sphaeropleales and Volvocales/Chlamydomonadales. To define the role of S transporters in chromium tolerance, we analyzed the expression of SULTRs and SULPs components of the chloroplast ABC transporter in two strains of S. acutus with different Cr(VI) sensitivity. Their differential expression in response to Cr(VI) exposure and S availability seems directly linked to Cr(VI) tolerance, confirming the role of sulfate uptake/assimilation pathways in the metal stress response. The SULTRs up-regulation, observed in both strains after S-starvation, may directly contribute to enhancing Cr-tolerance by limiting Cr(VI) uptake and increasing sulfur availability for the synthesis of sulfur-containing defense molecules.

Preparation of bio-oil from Scenedesmus acutus using thermochemical liquefaction in a 1 L reactor

Biomass from microalgae is a potential feedstock for biofuels production. It poses no threat to food security as it does not compete with agricultural crops for arable land. Scenedesmus acutus was used as feedstock to produce bio-oil in a large liquefaction reactor. The influence of reaction temperature (280–360ºC), reaction atmosphere (N2 or CO2) and solvent on bio-oil yield, C-16 fatty acid yield and oil properties were investigated. Oils were characterised using gas chromatography, Fourier transform infrared (FTIR) spectroscopy and ultimate analysis. Higher bio-oil yields were obtained in a CO2 atmosphere (250 g.kg-1 dry microalgae) than in a N2 atmosphere (210 g.kg-1 dry microalgae) whilst higher C16 fatty acid concentrations (600 g.kg-1 bio-oil) were recorded in N2 atmosphere compared to oil prepared in a CO2 atmosphere (500 g.kg-1 bio-oil). The oil yield increased to a maximum at 320°C, after which there were no significant changes. Highest bio-oil yields (425 g.kg-1 dry microalgae) were obtained in ethanol as solvent. FTIR spectroscopy and ultimate analysis showed that proteins present in the feedstock were degraded by breakage of peptide linkages, and nitrogen present in the oils is peptide fragments from protein degradation. The carbon content of all produced oils was high, but the hydrogen content was low, leading to low hydrogen/carbon ratios. Energy consumption and energy efficiency calculations showed that liquefaction in both reaction atmospheres results in a net energy gain, and a CO2 atmosphere is best for high energy efficiency.

Colony formation in three species of the family Scenedesmaceae (Desmodesmus subspicatus, Scenedesmus acutus, Tetradesmus dimorphus) exposed to sodium dodecyl sulfate and its interference with grazing of Daphnia galeata

By mimicking the info-chemicals emitted by grazers, the common anionic surfactant sodium dodecyl sulfate (SDS) can induce colony formation in the green algal genus Scenedesmus at environmentally relevant concentrations. The morphogenetic effects can hinder the feeding efficiency of grazers, reducing energy flow along the pelagic food chain from Scenedesmus to consumers. Despite this potential ecological risk, few studies exist on whether the SDS-triggered induction of colonies is common in other species of the family Scenedesmaceae. Here, we investigated the effects of SDS on the growth and morphology of three species of Scenedesmaceae (Desmodesmus subspicatus, Scenedesmus acutus, and Tetradesmus dimorphus) and on the clearance rates of Daphnia galeata grazing on the SDS-induced colonies. SDS triggered colony formation in all algal species at concentrations nonlethal to them; however, the induction levels of colony formation were generally lower than for those in the Daphnia culture medium. We also found that the SDS-induced colonial algae reduced D. galeata clearance rates. Our results highlight the potential effect of SDS on the Daphnia–Scenedesmaceae system by evoking the morphological response of Scenedesmaceae at concentrations below those that exert toxicity. Such disruptive effects of pollutants on predator–prey interactions should be considered within the framework of ecological risk assessments.

Efecto de efluentes municipales en el crecimiento y contenido de lípidos de la microalga Scenedesmus acutus en laboratorio

El objetivo de este estudio fue evaluar el efecto de las aguas residuales municipales (ARM) de la laguna de estabilización secundaria “Las Gaviotas”, (Nuevo Chimbote, Ancash-Perú). sobre el crecimiento poblacional y contenido de lípidos de la microalga Scenedesmus acutus. Los ensayos fueron realizados por triplicado dosificando cultivos de S. acutus con 25, 50, 75 y 100 % de ARM y un cultivo control con HM (Merino, 1999) durante siete días. Las concentraciones 50, 75 y 100 % de ARM alcanzaron mayores tasas de crecimiento (u) que el control (0,461; 0,467; 0,479 y 0,453 día-1, respectivamente) y elevados contenidos de lípidos (24,47; 23,94; 23,64 y 21,78 %), para los cultivos dosificados con 50, 75, 100% de ARM y control, respectivamente en el quinto día. El contenido de nitrógeno fue menor en los cultivos dosificados con ARM. Los cultivos de S. acutus dosificados con ARM presentaron altas tasas de crecimiento y contenido de lípidos que los controles, debido al menor contenido de nitrógeno.