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M Mota

Publications and source records attributed to M Mota.

At least 19 recordsLinked to original sources
PubMed2006

Utilisation of controlled pore topology for the separation of bioparticles in a mixed-glass beads column.

To study the flow of shaped particles in porous media, elution of spherical and rod-like micro-organisms was performed through beds of spherical glass beads. A 0.04 cm/s constant flow rate was used with 5 microm yeast suspensions, 1 microm latex micro-spheres and rod-like bacilli Lactobacillus bulgaricus 6 microm long and 0.5 microm in diameter. Yeast cells' diameter is close to the bacilli length and micro-spheres have the same diameter as bacilli. All particle types have similar density. To make the different packing beds, 1.125 mm coarse beads and 0.1115 mm fine beads were used. Experiments were carried out using a column loaded with the binary packing (volume fraction of coarse particles in the mixture 0.7) or a monosize packing with the same amount of coarse or fine particles as used in the binary packing. Analysis of experimental results was based on two models: pure exclusion effect and hydrodynamic separation model [hydrodynamic chromatography (HDC)]. Results for spheres show that the classic HDC model fits to the experimental data whenever the ratio of particle size to the pathway bend scale is high ( approximately 1/100, micro-spheres). However, if this ratio increases and becomes approximately 1/20, the HDC model needs to be corrected due to the effect of channel wall curvature on exclusion. This led to a modified HDC equation of the form R=B/(1+2lambda-2.8lambda(2)), where R is the retention, lambda is the aspect ratio and constant B>or=1. Bacillus separation follows an exclusion mechanism, since pore topology is important in the separation of shaped particles when the aspect ratio approaches lambda=0.1. In the case of a binary packing bed, rod-like particles display a different behaviour than the one exhibited by the spherical particles of the same scale as bacilli, either in length or in diameter. This may be explained by the interaction between rod-like bacilli and the bed's pore topology. A generalised exclusion model for particles was proposed to be R=A/(1-lambda)(z), where A is the coefficient proportional to the tortuosity and the parameter z=1, 2 or 3 depends mainly on pore shape. Controlled pore topology opens interesting applications for bio-separation (in porous micro-fluidic devices, deep bed filtration) and might be especially important for macromolecules and micro-organisms separation with different shapes.

Bacillus↗
PubMed2006

Ultrasonic characterization of granites obtained from industrial quarries of Extremadura (Spain).

The industry of ornamental rocks, such as granites, represents one of the most important industrial activities in the region of Extremadura, SW Spain. A detailed knowledge of the intrinsic properties of this natural stone and its environmental evolution is a required goal in order to fully characterize its quality. In this work, two independent NDT acoustic techniques have been used to measure the acoustic velocity of longitudinal waves in different prismatic granitic-samples of industrial quarries. A low-frequency transceiver set-up, based on a high-voltage BPV Steinkamp instrument and two 50 kHz probes, has been used to measure pulse travel times by ultrasonic through-transmission testing. In complementary fashion, an Erudite MK3 test equipment with an electromagnetic vibrator and two piezoelectric sensors has also been employed to measure ultrasonic velocity by means of a resonance-based method, using the same types of granite varieties. In addition, a comprehensive set of physical/mechanical properties have also been analyzed, according to Spanish regulations in force, by means of alternative methods including destructive techniques such as strength, porosity, absorption, etc. A large number of samples, representing the most important varieties of granites from quarries of Extremadura, have been analyzed using the above-mentioned procedures. Some results obtained by destructive techniques have been correlated with those found using ultrasonic techniques. Our experimental setting allowed a complementary characterization of granite samples and a thorough validation of the different techniques employed, thus providing the industry of ornamental rocks with a non-destructive tool that will facilitate a more detailed insight on the properties of the rocks under study.

Journal Article↗
PubMed2006

Bisexual branching processes in a genetic context: the extinction problem for Y-linked genes.

In this paper the inheritance of a Y-linked gene with alleles R and r in a population with both females and males is modelled using a two-type bisexual branching process. It is assumed that the reproductive distribution associated with the R allele can differ from the associated with the r allele and that females prefer to mate with a male having the R allele rather than with a male with the r allele. Under these assumptions, we provide some conditions for the extinction and/or survival of both alleles in the population. These conditions depend on the magnitudes of the average number of females and males per mating unit. Moreover, the almost sure extinction of the r allele is independent of the behaviour of the R allele. On the other hand, the survival of the R allele with positive probability may depend strongly on the reproductive behaviour of the other allele. Theoretical results are illustrated by means of simulated examples and some open problems are proposed to the reader as conjectures.

Alleles↗
PubMed2005

Anaerobic biodegradation of oleic and palmitic acids: evidence of mass transfer limitations caused by long chain fatty acid accumulation onto the anaerobic sludge.

Palmitic acid was the main long chain fatty acids (LCFA) that accumulated onto the anaerobic sludge when oleic acid was fed to an EGSB reactor. The conversion between oleic and palmitic acid was linked to the biological activity. When palmitic acid was fed to an EGSB reactor it represented also the main LCFA that accumulated onto the sludge. The way of palmitic acid accumulation was different in the oleic and in the palmitic acid fed reactors. When oleic acid was fed, the biomass-associated LCFA (83% as palmitic acid) were mainly adsorbed and entrapped in the sludge that became "encapsulated" by an LCFA layer. However, when palmitic acid was fed, the biomass-associated LCFA (the totality as palmitic acid) was mainly precipitated in white spots like precipitates in between the sludge, which remained "non-encapsulated." The two sludges were compared in terms of the specific methanogenic activity (SMA) in the presence of acetate, propionate, butyrate, and H(2)CO(2), before and after the mineralization of similar amounts of biomass-associated LCFA (4.6 and 5.2 g COD-LCFA/g of volatile suspended solids (VSS), for the oleic and palmitic acid fed sludge, respectively). The "non-encapsulated," sludge exhibited a considerable initial methanogenic activity on all the tested substrates, with the single exception of butyrate. However, with the "encapsulated" sludge only methane production from ethanol and H(2)/CO(2) was detected, after a lag phase of about 50 h. After mineralization of the biomass-associated LCFA, both sludges exhibited activities of similar order of magnitude in the presence of the same individual substrates and significantly higher than before. The results evidenced that LCFA accumulation onto the sludge can create a physical barrier and hinder the transfer of substrates and products, inducing a delay on the initial methane production. Whatever the mechanism, metabolic or physical, that is behind this inhibition, it is reversible, being eliminated after the depletion of the biomass-associated LCFA.

Acetates↗
PubMed2005

The bisexual branching process with population-size dependent mating as a mathematical model to describe phenomena concerning to inhabit or re-inhabit environments with animal species.

We consider the bisexual Galton-Watson branching process with population-size dependent mating as a mathematical model adequate for the description of some natural phenomena. More specifically we are interested in studying some questions about the problem of populating an environmental with new animal species or re-populating it with species which have previously disappeared.

Algorithms↗
PubMed2005

Decalactone production by Yarrowia lipolytica under increased O2 transfer rates.

Yarrowia lipolytica converts methyl ricinoleate to gamma-decalactone, a high-value fruity aroma compound. The highest amount of 3-hydroxy-gamma-decalactone produced by the yeast (263 mg l(-1)) occurred by increasing the k(L)a up to 120 h(-1) at atmospheric pressure; above it, its concentration decreased, suggesting a predominance of the activity of 3-hydroxyacyl-CoA dehydrogenase. Cultures were grown under high-pressure, i.e., under increased O(2) solubility, but, although growth was accelerated, gamma-decalactone production decreased. However, by applying 0.5 MPa during growth and biotransformation gave increased concentrations of dec-2-en-4-olide and dec-3-en-4-olide (70 mg l(-1)).

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed2004

Mineralization of LCFA associated with anaerobic sludge: Kinetics, enhancement of methanogenic activity, and effect of VFA.

Long-chain fatty acids (LCFA) associated with anaerobic sludge by mechanisms of precipitation, adsorption, or entrapment can be biodegraded to methane. The mineralization kinetics of biomass-associated LCFA were established according to an inhibition model based on Haldane's enzymatic inhibition kinetics. A value around 1,000 mg COD-LCFA..g VSS(-1) was obtained for the optimal specific LCFA content that allowed the maximal mineralization rate. For sludge with specific LCFA contents of 2,838 +/- 63 and 4,571 +/- 257 mg COD-LCFA..g VSS(-1), the specific methanogenic activities in the presence of acetate, butyrate, and H(2)/CO(2) were significantly enhanced after the mineralization of the biomass-associated LCFA. For sludge with a specific LCFA content near the optimal value defined by the kinetic model, the effect of adding VFA to the medium was studied during the mineralization of the biomass-associated LCFA. Different patterns were obtained for each individual substrate. Acetate and butyrate were preferentially consumed by the consortium, but in the case of propionate no evidence of a sequential consumption pattern could be withdrawn. It was concluded that LCFA do not exert a bactericidal neither a permanent toxic effect toward the anaerobic consortia. A discussion is addressed to the relative roles of a reversible inhibitory effect and a transport limitation effect imposed by the LCFA surrounding the cells.

Bacteria, Anaerobic↗
PubMed2004

Morphological and physiological changes in Saccharomyces cerevisiae by oxidative stress from hyperbaric air.

Increase in air or oxygen pressure in microbial cell cultures can cause oxidative stress and consequently affect cell physiology and morphology. The behaviour of Saccharomyces cerevisiae grown under hyperbaric atmospheres of air and pure oxygen was studied. A limit of 1.0 MPa for the air pressure increase (i.e. 0.21 MPa of oxygen partial pressure) in a fed-batch culture of S. cerevisiae was established. Values of 1.5 MPa air pressure and 0.32 MPa pure oxygen pressure strongly inhibited the metabolic activity and the viability of the cells. Also, morphological changes were observed, especially cell-size distribution and the genealogical age profile. Pressure caused cell compression and an increase in number of aged cells. These effects were attributed to oxygen toxicity since similar results were obtained using air or oxygen, if oxygen partial pressure was equal to or higher than 0.32 MPa. The activity of the antioxidant enzymes, catalase and superoxide dismutase (SOD) (cytosolic and mitochondrial isoformes) indicated that the enzymes have different roles in oxidative stress cell protection, depending on other factors that affect the cell physiological state.

Adaptation, Physiological↗
PubMed2004

Development of image analysis techniques as a tool to detect and quantify morphological changes in anaerobic sludge: II. Application to a granule deterioration process triggered by contact with oleic acid.

Image analysis techniques are applied to monitor the morphological changes in granular sludge present in an expanded granular sludge blanket (EGSB) reactor fed with oleic acid. Deterioration of granular sludge was monitored along the trial period by measuring the percentage of aggregates smaller than 1 mm (in terms of Feret diameter) either in terms of projected area or in terms of number of aggregates. A good correlation was obtained between these values and the percentage of aggregates smaller than 1 mm were physically sorted and quantified by the volatile suspended solid content. The ratio of total filaments length to cross-sectional area of aggregates defined as LfA, was applied to quantify the dispersion level of the granular sludge, which increased until day 141 and remained almost invariant afterwards. LfA was sensitive to the sludge deterioration process and was able to indicate, with the anticipation of about 1 month, the most significant biomass washout episode that occurred in the trial period. A mechanism of filaments' release, detachment and selective washout was proposed to explain the action of LfA from this viewpoint. The equivalent diameter of the bottom aggregates larger than 1 mm increased with the increase on the amount of long chain fatty acids associated with the biomass by mechanisms of adsorption, precipitation, or entrapment. After a threshold value of about 200 mg COD-LCFA gVSS (COD = chemical oxygen demand; LCFA = long chain fatty acids; VSS = volatile suspended solids), a migration of granular sludge from the bottom to a top-floating layer was evident.

Anaerobiosis↗
PubMed2004

Development of image analysis techniques as a tool to detect and quantify morphological changes in anaerobic sludge: I. Application to a granulation process.

Image analysis techniques were developed and applied to quantify the process of anaerobic granulation in an expanded granular sludge blanket reactor (EGSB) fed with a synthetic substrate based on glucose [60-30% COD (chemical oxygen demand)] and volatile fatty acids (40-70% COD) over 376 days. In a first operation period that lasted 177 days, the aggregation of dispersed sludge was quantitatively monitored through the recognition and quantification of aggregates and filaments. A parameter defined as the ratio between the filaments' length and the aggregates projected area (LfA) has proven to be sensitive to detect changes in the aggregation status of the anaerobic sludge. The aggregation time-defined as the moment when a balance between filaments' length and aggregates' size was established-was recognized through the LfA. The percentage of projected area of aggregates within three size ranges (0.01-0.1 mm, 0.1-1 mm, and >1 mm, equivalent diameter) reflected the granular size spectrum during the aggregation process. When sudden increases on the upflow velocity and on the organic loading rate were applied to the previously formed granules, the developed image analysis techniques revealed to be good indicators of granular sludge stability, since they were sensitive to detected filaments release, fragmentation, and erosion that usually leads to washout. The specific methanogenic activities in the presence of acetate, propionate, butyrate, and H(2)/CO(2) increased along the operation, particularly relevant was the sudden increase in the specific hydrogenophilic activity, immediately after the moment recognized as aggregation time.

Algorithms↗
PubMed2004

Enzymatic versus chemical deinking of non-impact ink printed paper.

Enzymatic versus chemical deinking is examined for MOW and photocopy prints. Several enzymatic preparations and two fibre/ink particle separation methods are tested. Deinking was monitored by image analysis and standard pulp and paper characterisation procedures. The effectiveness of the fibre/ink particle separation method depends on the ink particle's size: for smaller particles a washing step is recommended whereas for larger particles, the use of flotation is necessary. The enzymatic treatment is a competitive alternative for MOW and photocopy paper deinking. However, the process requires the selection of an adequate enzymatic preparation for each paper grade.

Biodegradation, Environmental↗
PubMed2004

Effect of hyperbaric stress on yeast morphology: study by automated image analysis.

The effects of hyperbaric stress on the morphology of Saccharomyces cerevisiae were studied in batch cultures under pressures between 0.1 MPa and 0.6 MPa and different gas compositions (air, oxygen, nitrogen or carbon dioxide), covering aerobic and anaerobic conditions. A method using automatic image analysis for classification of S. cerevisiae cells based on their morphology was developed and applied to experimental data. Information on cell size distribution and bud formation throughout the cell cycle is reported. The results show that the effect of pressure on cell activity strongly depends on the nature of the gas used for pressurization. While nitrogen and air to a maximum of 0.6 MPa of pressure were innocuous to yeast, oxygen and carbon dioxide pressure caused cell inactivation, which was confirmed by the reduction of bud cells with time. Moreover, a decrease in the average cell size was found for cells exposed for 7.5 h to 0.6 MPa CO2.

Air Pressure↗
PubMed2004

Carbohydrate carbon sources induce loss of flocculation of an ale-brewing yeast strain.

AIMS: To identify the nutrients that can trigger the loss of flocculation under growth conditions in an ale-brewing strain, Saccharomyces cerevisiae NCYC 1195. METHODS AND RESULTS: Flocculation was evaluated using the method of Soares, E.V. and Vroman, A. [Journal of Applied Microbiology (2003) 95, 325]. Yeast growth with metabolizable carbon sources (glucose, fructose, galactose, maltose or sucrose) at 2% (w/v), induced the loss of flocculation in yeast that had previously been allowed to flocculate. The yeast remained flocculent when transferred to a medium containing the required nutrients for yeast growth and a sole nonmetabolizable carbon source (lactose). Transfer of flocculent yeast into a growth medium with ethanol (4% v/v), as the sole carbon source did not induce the loss of flocculation. Even the addition of glucose (2% w/v) or glucose and antimycin A (0.1 mg l(-1)) to this culture did not bring about loss of flocculation. Cycloheximide addition (15 mg l(-1)) to glucose-growing cells stopped flocculation loss. CONCLUSIONS: Carbohydrates were the nutrients responsible for stimulating the loss of flocculation in flocculent yeast cells transferred to growing conditions. The glucose-induced loss of flocculation required de novo protein synthesis. Ethanol prevented glucose-induced loss of flocculation. This protective effect of ethanol was independent of the respiratory function of the yeast. SIGNIFICANCE AND IMPACT OF THE STUDY: This work contributes to the elucidation of the role of nutrients in the control of the flocculation cycle in NewFlo phenotype yeast strains.

Antifungal Agents↗
PubMed2004

A comparison of purine derivatives excretion with conventional methods as indices of microbial yield in dairy cows.

Three multiparous, ruminally and duodenally cannulated Holstein-Friesian milking cows (558 +/- 14 kg BW) with a mean milk yield of 19.9 +/- 1.4 kg/d in their 4th mo of lactation were fed a mixed diet of forage and concentrate at 100, 85, and 75% of ad libitum intake in a 3 x 3 Latin square design. Duodenal digesta flow was estimated using the dual-phase technique in which Cr-EDTA and Yb-acetate were used as liquid and solid markers, respectively. Microbial N (MN) was estimated using the duodenal flow of purine bases (PB); bacterial isolates from the rumen liquid and solid phases were used as references. Additionally, duodenal flow of PB and MN were estimated indirectly using the excretion of purine derivatives (PD) in urine and milk. Duodenal flow of PB and derived MN tended to decrease with feed restriction (from 258 to 154 mmol/d and 123.5 to 74.4 g/d, respectively). Estimates of PB and MN based on urinary PD showed the same trend, and decreases in PB (from 314 to 266 mmol/d, using LAB) were statistically significant. Using LAB, efficiencies of microbial protein synthesis in the ad libitum treatment were 12.9 and 17.0 g of MN/g of organic matter apparently digested in the rumen when estimated using duodenal PB and urinary excretion of PD, respectively. Urinary excretion of PD closely reflected changes in duodenal flow of PB as a result of feed restriction.

Ammonia↗
PubMed2003

Growth and beta-galactosidase activity in cultures of Kluyveromyces marxianus under increased air pressure.

AIMS: To investigate the effect of total air pressure raise on cell growth and intracellular beta-galactosidase activity in batch cultures of Kluyveromyces marxianus CBS 7894. METHODS AND RESULTS: A pressurized bioreactor was used for K. marxianus batch cultivation under increased air pressure from 1.2 to 6 bar. Under these conditions no inhibition of cell growth was observed. Moreover, the improvement of the oxygen transfer rate (OTR) from the gas to the culture medium by pressurization led to an enhancement of the cell growth rate obtained at atmospheric pressure without aeration. The specific beta-galactosidase productivity increased from 5.8 to 17.0 U gCD-1 h-1 using a 6-bar air pressure instead of air at atmospheric pressure. The antioxidant enzyme superoxide dismutase (SOD) was slightly induced by the air pressure raise, which indicates that the defensive mechanisms of the cells can cope with an air pressure up to 6 bar. CONCLUSIONS: These experiments showed that the increase of air pressure up to 6 bar is an alternative to other methods of preventing the oxygen limitation and can be applied in the beta-galactosidase production by K. marxianus. SIGNIFICANCE AND IMPACT OF THE STUDY: The results here reported proved that, in what biological aspects are concerned, it is possible to use the air pressure increase as an optimization parameter of beta-galactosidase production in high-density cell cultures of K. marxianus strains.

Air Pressure↗
PubMed2003

Image analysis, methanogenic activity measurements, and molecular biological techniques to monitor granular sludge from an EGSB reactor fed with oleic acid.

Morphological changes in anaerobic granular sludge fed with increasing loads of oleic acid were quantified by image analysis. The combination of this technique with data on the accumulation of adsorbed long chain fatty acid and with the molecular characterization of microbial community gave insight into the mechanisms of sludge disintegration, flotation and washout. It was found that the bacterial domain was more affected than the archaeal domain during this process. However, no acetoclastic activity and onlya residual hydrogenotrophic activity were detected in the sludge at the end of the operation.

Adsorption↗
PubMed2003

Accumulation of long chain fatty acids onto anaerobic sludge under steady state and shock loading conditions: effect on acetogenic and methanogenic activity.

Accumulation of substrate onto the biomass was quantified under steady-state and shock conditions in a fixed bed reactor fed with an oleic acid-based synthetic effluent. The accumulation of substrate onto the sludge was more dependent on oleic acid concentration than on oleic acid loading rate and decreased the acetogenic, acetoclastic and hydrogenophilic activity. However, even when the methanogenic activity measurements indicate a severe inhibition, the anaerobic sludge was able to methanise efficiently the accumulated substrate that was mainly adsorbed LCFA. Methanogenic activity measurements for a sludge loaded with 2,861 mg COD/gVSS as LCFA, revealed that only hydrogenophilic activity was detected, whereas the methanogenic activities with acetate, propionate and butyrate as substrates were null. However the methanogenic activity of the same sludge after allowing the depletion of the adsorbed LCFA were significantly enhanced in the presence of all substrates, except in propionate. A discussion about the relative importance of metabolic inhibition and transport limitations for the anaerobic degradation of LCFA is launched.

Bacteria, Anaerobic↗