Fabrizio Di Caprio

Effect of Ca2+ concentration on Scenedesmus sp. growth in heterotrophic and photoautotrophic cultivation

The influence of Ca2+ concentration on the growth of the microalga Scenedesmus sp. in heterotrophic and photoautotrophic cultivations was investigated. Heterotrophic growth was induced by the addition of olive mill wastewaters (9% v·v-1) to the culture. Variations in the calcium concentration affected differently biomass production depending on whether microalgae were cultivated under heterotrophic or photoautotrophic regime. In photoautotrophic regime, increasing the calcium concentration from 20 to 230mg⋅L-1 decreased maximum cell concentration and growth rate. In heterotrophic cultivation, cell concentration and growth rate decreased with Ca2+ concentration increasing from 20 to 80mg⋅L-1 but then increased with Ca2+ concentration increasing to 230mg⋅L-1. Increasing calcium concentration invariably promoted cell aggregation. The precipitation of calcium phosphates can explain the decreasing growth rate and cell concentration attained with increasing calcium concentration, while the influence of Ca2+ concentration on the adsorption of phenols on suspended solids can explain the enhanced growth attained at large Ca2+ concentration under heterotrophic regime. Implications of the illustrated results for industrial scale application of microalgae are thoroughly discussed.

Two stage process of microalgae cultivation for starch and carotenoid production

Biotechnological processes based on microalgae cultivation are promising for several industrial applications. Microalgae are photoautotrophic microorganisms and can thus grow by using renewable and inexpensive resources as sunlight, inorganic salts, water and CO2. They can store high amounts of neutral lipids (bioil), carbohydrates (mainly starch), carotenoids (such as lutein, astaxanthin, β-carotene), proteins and other molecules. Productions of lipids and carbohydrates have recently received an increasing interest for biofuel production, while proteins, carotenoids and other minor products are usable as feed additives and nutraceutical compounds. Biofuel production from microalgae is not yet economically sustainable, while there are different industrial plants in the world for the production of high values chemicals as carotenoids. Starch production from microalgae has been investigated mainly for the production of biofuels (e.g. bioethanol) by successive fermentation. However, purified starch can be used for other aims such as the production of bioplastics. Superior plants as corn, potato and wheat are currently used for this purpose. However, there are different environmental and economic issues related to the use of fertile lands and edible plants for these kinds of productions. Microalgae can solve these social and ethical issues because they can grow on nonfertile lands and also reach starch productivity per hectare higher than plants. In this work, the production of starch and carotenoids from Scenedesmus sp. microalgal strain is reported. A two-stage process has been developed in order to reduce operative and investment costs. In the first stage, microalgae are cultivated in photoautotrophic conditions and then, when biomass concentration rises and light becomes a limiting factor for growth, microalgae are transferred to a heterotrophic reactor. In this reactor, microalgae are cultivated by using wastewaters as source of nutrients (mainly organic carbon). Microalgae use organic carbon to synthesize starch and simultaneously reduce the content of pollutants in the wastewater (codepuration). Biomass separated by the culture medium is treated for the extraction of lipids containing different antioxidant carotenoids (such as astaxanthin and lutein) and starch granules as raw material for biopolymers.

Quantification of Tetradesmus obliquus (Chlorophyceae) cell size and lipid content heterogeneity at single‐cell level

Much of our current knowledge of microbial growth is obtained from studies at a population level. Driven by the realization that processes that operate within a population might influence a populations behavior, we sought to better understand Tetradesmus obliquus (formerly Scenedesmus obliquus) physiology at the cellular level. In this work, an accurate pretreatment method to quantitatively obtain single cells of T. obliquus, a coenobia‐forming alga, is described. These single cells were examined by flow cytometry for triacylglycerol (TAG), chlorophyll, and protein content, and their cell sizes were recorded by coulter counter. We quantified heterogeneity of size and TAG content at single‐cell level for a population of T. obliquus during a controlled standard batch cultivation. Unexpectedly, variability of TAG content per cell within the population increased throughout the batch run, up to 400 times in the final stage of the batch run, with values ranging from 0.25 to 99 pg · cell−1. Two subpopulations, classified as having low or high TAG content per cell, were identified. Cell size also increased during batch growth with average values from 36 to 70 μm3 · cell−1; yet cell size variability increased only up to 16 times. Cell size and cellular TAG content were not correlated at the single‐cell level. Our data show clearly that TAG production is affected by cell‐to‐cell variation, which suggests that its control and better understanding of the underlying processes may improve the productivity of T. obliquus for industrial processes such as biodiesel production.

Effect of lipids and carbohydrates extraction on astaxanthin stability in Scenedesmus sp.

Elevated costs of biomass downstream processing represent a severe limit to the industrial development of microalgal production systems. Biorefinery solutions allowing simultaneously deriving biofuels and extracting high value compounds must be explored to enhance economic feasibility. In this work, the possibility to extract carbohydrates, lipids and astaxanthin from a strain of Scenedesmus sp. is investigated. The analysis is mainly focused on analyzing the effect of consolidated procedures of extraction of carbohydrates and lipids on the degradation and recovery of astaxanthin. Microalgae were cultivated till achieving stationary phase and maintained in this phase to enhance lipids and astaxanthin accumulation. The fractions of total lipids, carbohydrates and astaxanthin of the produced biomass were 17 %, 33 % and 0.02 % respectively. No statistically significant difference in the astaxanthin content determined following Soxhlet extraction and a more gentle extraction method (Yuan et al. 2002) was found. The effect of transesterification conditions was also evaluated revealing a scarce degradation of astaxanthin in response to the achievement of elevated temperature, NaOH and dissolved oxygen concentrations. Reductions in astaxanthin content were in contrast obtained in response to the addition of H2SO4. These reductions were proportional to acid sample concentration. However a regeneration of astaxanthin was obtained by NaOH addition indicating reversibility of the degradation process. In accordance with these results, the possibility to perform biomass saccharification for carbohydrate extraction at progressively lower acid concentrations was investigated.

Lanthanum biosorption by different saccharomyces cerevisiae strains

Lanthanum Biosorption by Different Saccharomyces cerevisiae Strains Fabrizio Di Caprio*, Pietro Altimari, Elena Zanni, Daniela Uccelletti, Luigi Toro, Francesca Pagnanelli Dipartimento di Chimica, Università “Sapienza” di Roma, Piazzale Aldo Moro 5, 00185, Roma, Italia. Dipartimento di Biologia e Biotecnologie “C.Darwin”, Università “Sapienza” di Roma, Piazzale Aldo Moro 5, 00185, Roma, Italia. fabrizio.dicaprio@uniroma1.it

Biosorption of Copper by Saccharomyces cerevisiae : From Biomass Characterization to Process Development

Biosorption offers a competitive technological solution to the removal of heavy metals from wastewaters. Nevertheless, large-scale application of biosorption is still hindered by the absence of systematic methodologies for product and process design. Crucial role is played by the development of models that can describe the effect of operating conditions on biosorption equilibrium and kinetics and thus drive the rational process design. In this contribution, biosorption of copper onto a wild-type strain of Saccharomyces cerevisiae is analyzed. The analysis is structured in a way that allows reviewing and discussing the main stages of process development. Type and concentration of the biomass active sites were determined by fitting mechanistic equilibrium models accounting for the distribution of the site protonation constants to potentiometric titration data. Equilibrium biosorption tests were performed to determine the dependence of the biosorption capacity on pH (3 and 5) and metal liquid concentration (0–120 ppm). The immobilization of biomass by calcium alginate was performed to produce composite sorbent beads with different biomass contents. An experimental analysis was performed to characterize the kinetics and the equilibrium of copper biosorption onto the produced beads. These data were exploited to identify kinetic and equilibrium models describing the competitive biosorption of protons and copper ions onto the beads. A mathematical model was derived to describe the transport of copper and protons in a biosorption column packed by the produced beads. The column mathematical model was validated by recourse to the experimental data derived by the operation of lab-scale packed column (length 15 cm, diameter 1.7 cm).