Production of ethanol by immobilized Saccharomyces bayanus in an extractive fermentation system

An extractive fermentation system using immobilized yeast cells was developed to study the ethanol production at high sugar concentrations. Organic acids were used as extracting solvents of ethanol and their toxicity was tested in free and k-carrageenan entrapped cell preparations. Immobilization seems to protect cells against solvent toxicity, when long-chain organic acids, e.g., oleic acid, were used, probably due to steric and diffusional limitations, the free cells not being viable at high oleic acid concentrations. The entrapped cells also present a higher metabolic activity than their free counterparts at high glucose concentrations. A solution of 300 g/L of glucose was totally fermented by the immobilized yeast cells, which when free cannot normally convert more than 200 g/L. In situ recovery of ethanol by oleic acid in a batch immobilized cell system led to higher ethanol productivities and to the fermentation of 400 g/L, when an oleic acid/medium ratio of 5 was used.     

Influence of Calcium Ion on Ethanol Tolerance of Saccharomyces bayanus and Alcoholic Fermentation by Yeasts

The addition of Ca²⁺ (as CaCl₂) in optimal concentrations (0.75 to 2.0 mM) to a fermentation medium with a trace contaminating concentration of Ca²⁺ (0.025 mM) led to the rapid production of higher concentrations of ethanol by Saccharomyces cerevisiae, Saccharomyces bayanus, and Kluyveromyces marxianus. The positive effect of calcium supplementation (0.75 mM) on alcoholic fermentation by S. bayanus was explained by the increase in its ethanol tolerance. The ethanol inhibition of growth and fermentation followed the equation μ_xi = μ_oi [1 - (X/X_mi)]ⁿⁱ, where μ_oi and μ_xi are, respectively, the specific growth (i = g) and fermentation (i = f) rates in the absence or presence of a concentration (X) of added ethanol, and X_mi is the maximal concentration of ethanol which allows growth or fermentation. The toxic power is given by n_i. In Ca²⁺ - supplemented medium (0.75 mM), n_g = 0.42 for growth and n_f = 0.43 for fermentation compared with 0.52 and 0.55, respectively, in unsupplemented medium; for both media, X_mg = 10% (vol/vol) and X_mf = 13% (vol/vol). For lethal concentrations of ethanol, the specific death rates were minimal for cells that were grown and incubated with ethanol in medium with an optimal concentration of Ca²⁺, maximal for cells grown and incubated with ethanol in unsupplemented medium, and intermediate for cells grown in unsupplemented medium and incubated with ethanol in calcium-supplemented medium. The effect of Ca²⁺ on the acidification curve of energized cells in the presence of ethanol was found to be closely associated with its protective effect on growth, fermentation, and viability.     

Immobilization studies of whole microbial cells on transition metal activated inorganic supports

Summary Whole cells of Saccharomyces bayanus, Saccharomyces cerevisiae and Zymomonas mobilis were immobilized by chelation/metal-link processes onto porous inorganic carriers. The immobilized yeast cells displayed much higher sucrose hydrolyzing activities (90–517 U/g) than the bacterial, Z. mobilis, cells (0.76–1.65 U/g). The yeast cells chelated on hydrous metal oxide derivative of pumice stone presented higher initial -d-fructofuranosidase (invertase, EC 3.2.1.26) activity (161–517 U/g) than on other derivatives (90–201 U/g). The introduction of an organic bridge between the cells and the metal activator led to a decrease of the initial activity of the immobilized cells, however S. cerevisiae cells immobilized on the carbonyl derivative of titanium (IV) activated pumice stone, by covalent linkage, displayed a very stable behaviour, which in continuous operation at 30° C show only a slightly decrease on invertase activity for a two month period (half-life=470 days). The continuous hydrolysis of a 2% w/v sucrose solution at 30° C in an immobilized S. cerevisiae packed bed reactor was described by a simple kinetic model developed by the authors (Cabral et al., 1984a), which can also be used to predict the enzyme activity of the immobilized cells from conversion degree data.     

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.Author for correspondence     

Volume regulation by flounder red blood cells in anisotonic media

The nucleated high K, low Na red blood cells of the winter flounder demonstrated a volume regulatory response subsequent to osmotic swelling or shrinkage. During volume regulation the net water flow was secondary to net inorganic cation flux. Volume regulation the net water flow was secondary to net inorganic cation flux. Volume regulation after osmotic swelling is referred to as regulatory volume decrease (RVD) and was characterized by net K and water loss. Since the electrochemical gradient for K is directed out of the cell there is no need to invoke active processes to explain RVD. When osmotically shrunken, the flounder erythrocyte demonstrated a regulatory volume increase (RVI) back toward control cell volume. The water movements characteristic of RVI were a consequence of net cellular NaCl and KCl uptake with Na accounting for 75 percent of the increase in intracellular cation content. Since the Na electrochemical gradient is directed into the cell, net Na uptake was the result of Na flux via dissipative pathways. The addition of 10(-4)M ouabain to suspensions of flounder erythrocytes was without effect upon net water movements during volume regulation. The presence of ouabain did however lead to a decreased ration of intracellular K:Na. Analysis of net Na and K fluxes in the presence and absence of ouabain led to the conclusion that Na and K fluxes via both conservative and dissipative pathways are increased in response to osmotic swelling or shrinkage. In addition, the Na and K flux rate through both pump and leak pathways decreased in a parallel fashion as cell volume was regulated. Taken as a whole, the Na and K movements through the flounder erythrocyte membrane demonstrated a functional dependence during volume regulation.     

Biological treatment of phenolic wastes: Comparison between free and immobilized cell systems

Summary Phenol degradation by free and immobilized cells ofFusarium flocciferum was studied in a chemostat at steady-state conditions. For the free cell system the dilution rates varied from 0.02 to 0.13h^–1, with a total phenol removal up to 0.08h^–1. Wash-out seemed to set in at 0.11h^–1. The immobilized cells showed virtually complete phenol utilization at 1g/l, over a period of four months. At D=0.2h^–1 and above 1g/l phenol, the complete phenol removal is not achieved: a progressive increase in the outlet concentration was observed attaining a value of 284mg/l at 1.5g/l.     

Investigation of the operational stabilities and kinetics of glucoamylase immobilized on alkylamine derivatives of titanium(IV)-activated porous inorganic supports

Glucoamylase (exo-1,4-α-d-glucosidase, EC 3.2.3.1) was coupled to several porous silica matrices by an improved metal-link/chelation process using alkylamine derivatives of titanium(IV)-activated supports. In order to select the titanium activation procedure which gave stable enzyme preparations, long-term stability tests were performed. The immobilized glucoamylase preparations, in which the carrier was activated to dryness with a 15% w/v TiCl₄ solution, displayed very stable behaviour, with half-lives of ～60 days. The optimum operating conditions were determined for these preparations. There are significant differences between the behaviour of the immobilized enzyme and the free enzyme. The apparent K_m increased on immobilization due to diffusional resistances. The pH optimum for the immobilized preparation showed a slight shift to acid pH relative to that of the soluble enzyme. Also, the optimum temperature descreased to 60°C after immobilization. In order to test Michaelis-Menten kinetics at high degrees of conversion, time-course analysis of soluble starch hydrolysis was performed. It was observed that simple Michaelis-Menten kinetics are not applicable to the free/immobilized glucoamylase-starch system at high degrees of conversion.     

Biodeterioration of Mayan buildings at uxmal and tulum,Mexico

Uxmal and Tulum are two important Mayan sites in the Yucatan peninsula. The buildings are mainly composed of limestone and grey/black discoloration is seen on exposed walls and copious greenish biofilms on inner walls. The principal microorganisms detected on interior walls at both Uxmal and Tulum were cyanobacteria; heterotrophic bacteria and filamentous fungi were also present. A dark‐pigmented mitosporic fungus and Bacillus cereus, both isolated from Uxmal, were shown to be acidogenic in laboratory cultures. Cyanobacteria belonging to rock‐degrading genera Synechocystis and Gloeocapsa were identified at both sites. Surface analysis previously showed that calcium ions were present in the biofilms on buildings at Uxmal and Tulum, suggesting the deposition of biosolubilized stone. Apart from their potential to degrade the substrate, the coccoid cyanobacteria supply organic nutrients for bacteria and fungi, which can produce organic acids, further increasing stone degradation.     

Botanical affinity of pollen harvested by Apis mellifera L. in a semi-arid area from Bahia,Brazil

We analysed the botanical composition of pollen harvested by Apis mellifera L. in the Canudos Biological Station, Bahia, Brazil, and the influence of climatic factors on pollen sample composition was assessed. Forty-six pollen types were identified belonging to species occurring in the study area. The family Leguminosae was of significant importance amongst the samples, represented by ten pollen types. Diodia radula, Rhaphiodon echinus, and Mimosa misera pollen types occurred most constantly among the samples. We observed that isolated pollen class characterises samples analysed. It was also observed that pollen type richness is directly linked to rainfall, reflecting the strong influence of this climatic parameter on flowering intensity, and thus on the ability of the bees to obtain food resources.