Roberto Dorta-Guerra

On the influence of the culture conditions in bacterial antifouling bioassays and biofilm properties: Shewanella algae, a case study

BackgroundA variety of conditions (culture media, inocula, incubation temperatures) are employed in antifouling tests with marine bacteria. Shewanella algae was selected as model organism to evaluate the effect of these parameters on: bacterial growth, biofilm formation, the activity of model antifoulants, and the development and nanomechanical properties of the biofilms.The main objectives were:1) To highlight and quantify the effect of these conditions on relevant parameters for antifouling studies: biofilm morphology, thickness, roughness, surface coverage, elasticity and adhesion forces.2) To establish and characterise in detail a biofilm model with a relevant marine strain.ResultsBoth the medium and the temperature significantly influenced the total cell densities and biofilm biomasses in 24-hour cultures. Likewise, the IC50 of three antifouling standards (TBTO, tralopyril and zinc pyrithione) was significantly affected by the medium and the initial cell density. Four media (Marine Broth, MB; 2% NaCl Mueller-Hinton Broth, MH2; Luria Marine Broth, LMB; and Supplemented Artificial Seawater, SASW) were selected to explore their effect on the morphological and nanomechanical properties of 24-h biofilms. Two biofilm growth patterns were observed: a clear trend to vertical development, with varying thickness and surface coverage in MB, LMB and SASW, and a horizontal, relatively thin film in MH2. The Atomic Force Microscopy analysis showed the lowest Young modulii for MB (0.16 ± 0.10 MPa), followed by SASW (0.19 ± 0.09 MPa), LMB (0.22 ± 0.13 MPa) and MH2 (0.34 ± 0.16 MPa). Adhesion forces followed an inverted trend, being higher in MB (1.33 ± 0.38 nN) and lower in MH2 (0.73 ± 0.29 nN).ConclusionsAll the parameters significantly affected the ability of S. algae to grow and form biofilms, as well as the activity of antifouling molecules. A detailed study has been carried out in order to establish a biofilm model for further assays. The morphology and nanomechanics of S. algae biofilms were markedly influenced by the nutritional environments in which they were developed. As strategies for biofilm formation inhibition and biofilm detachment are of particular interest in antifouling research, the present findings also highlight the need for a careful selection of the assay conditions.

Effects of dietary fish oil substitution by Echium oil on enterocyte and hepatocyte lipid metabolism of gilthead seabream (Sparus aurata L.)

The fatty acid profile of vegetable oils (VOs), together with the poor ability of marine fish to convert polyunsaturated fatty acids (PUFA) to highly unsaturated fatty acids (HUFA), lead to important changes in the nutritional value of farmed fish fed VO, which include increased fat and 18:2n-6 and reduced n-3 HUFA. Echium oil (EO) has a good n-3/n-6 balance as well as an interesting profile with its high content of unusual fatty acids (SDA, 18:4n-3 and GLA, 18:3n-6) that are of increasing pharmacological interest. The effects of substituting 50 % of dietary fish oil (FO) by EO on gilthead seabream (Sparus aurata L.) enterocyte and hepatocyte lipid metabolism were studied. After 4months of feeding, cell viability, total lipid contents and lipid class compositions were not affected by EO. The cells clearly reflected the fatty acid profile of the EO showing increased SDA, GLA and its elongation product 20:3n-6, and only minorly decreased n-3 HUFA compared to other VO. Metabolism of [1-(14)C]18:2n-6 and [1-(14)C]18:3n-3 was also unaffected by EO in terms of total uptake, incorporation, beta-oxidation and elongation-desaturation activities.

Echium acanthocarpum hairy root cultures, a suitable system for polyunsaturated fatty acid studies and production

BackgroundThe therapeutic and health promoting role of highly unsaturated fatty acids (HUFAs) from fish, i.e. eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) are well known. These same benefits may however be shared by some of their precursors, the polyunsaturated fatty acids (PUFAs), such as stearidonic acid (SDA, 18:4 n-3). In order to obtain alternative sources for the large-scale production of PUFAs, new searches are being conducted focusing on higher plants oils which can contain these n-3 and n-6 C18 precursors, i.e. SDA and GLA (18:3n-6, γ-linolenic acid).ResultsThe establishment of the novel Echium acanthocarpum hairy root cultures represents a powerful tool in order to research the accumulation and metabolism of fatty acids (FAs) in a plant particularly rich in GLA and SDA. Furthermore, this study constitutes the first example of a Boraginaceae species hairy root induction and establishment for FA studies and production. The dominant PUFAs, 18:2n-6 (LA, linoleic acid) and 18:3n-6 (GLA), accounted for about 50% of total FAs obtained, while the n-3 PUFAs, 18:3n-3 (ALA, α-linolenic acid) and 18:4n-3 (SDA), represented approximately 5% of the total. Production of FAs did not parallel hairy root growth, and the optimal productivity was always associated with the highest biomass density during the culture period. Assuming a compromise between FA production and hairy root biomass, it was determined that sampling times 4 and 5 gave the most useful FA yields. Total lipid amounts were in general comparable between the different hairy root lines (29.75 and 60.95 mg/g DW), with the major lipid classes being triacylglycerols. The FAs were chiefly stored in the hairy roots with very minute amounts being released into the liquid nutrient medium.ConclusionsThe novel results presented here show the utility and high potential of E. acanthocarpum hairy roots. They are capable of biosynthesizing and accumulating a large range of polyunsaturated FAs, including the target GLA and SDA fatty acids in appreciable quantities.

Two-level experiments for binary response data

Information in a statistical experiment is often measured through the determinant of its information matrix. Under first order normal linear models, the determinant of the information matrix of a two-level factorial experiment neither depends on where the experiment is centered, nor on how it is oriented, and balanced allocations are more informative than unbalanced ones with the same number of runs. In contrast, under binary response models, none of these properties hold. The performance of two-level experiments for binomial responses is explored by investigating the dependence of the determinant of their information matrix on their location, orientation, range, presence or absence of interactions and on the relative allocation of runs to support points, and in particular, on the type of fractionating involved. Conventional wisdom about two-level factorial experiments, which is deeply rooted on normal response models, does not apply to binomial models. In binary response settings, factorial experiments should not be used for screening or as building blocks for binary response surface exploration, and there is no alternative to the optimal design theory approach to planning experiments.

Centralized and decentralized inventory policies for a single-vendor two-buyer system with permissible delay in payments

In todays business transactions, vendors usually offer their buyers a delay period in payment. This strategy has benefits to the vendor since it attracts new buyers who consider the delay period as a type of price reduction. In addition, permissible delay in payments also is advantageous for the buyers since they do not have to pay the vendor immediately after they receive the items. In contrast, the buyers can delay the payment until the end of the allowed period and during the credit period they can earn interest on the accumulated revenues. However, if the payment is not settled by the end of the credit period, a higher interest is charged. Under this scenario, an inventory model consisting of a single vendor which supplies an item to two different buyers is analyzed. First, we address the problem assuming that buyers and vendor are willing to cooperate and the integrated model is derived in terms of single-cycle policies. Next, we analyze a decentralized model where the buyers and the vendor make decisions independently. A numerical example is solved to illustrate both strategies. We carry out a computational study to compare integrated and decentralized policies. A sensitivity analysis is also performed to examine the effects of each parameter on both total costs. According to the computational results and the statistical analysis, in most scenarios the integrated policies outperform the decentralized strategies. HighlightsThe one-vendor two-buyer inventory system with permissible delay in payments is addressed.The problem is analyzed under both a cooperative and a non-cooperative environment.A numerical example is solved to illustrate the solutions approaches.Both solution procedures have been implemented and the computational results reveal that in most cases the integrated policies outperform the decentralized strategies.

Improvement of Polyunsaturated Fatty Acid Production in Echium acanthocarpum Transformed Hairy Root Cultures by Application of Different Abiotic Stress Conditions

Fatty acids are of great nutritional, therapeutic, and physiological importance, especially the polyunsaturated n-3 fatty acids, possessing larger carbon chains and abundant double bonds or their immediate precursors. A few higher plant species are able to accumulate these compounds, like those belonging to the Echium genus. Here, the novel E. acanthocarpum hairy root system, which is able to accumulate many fatty acids, including stearidonic and α-linolenic acids, was optimized for a better production. The application of abiotic stress resulted in larger yields of stearidonic and α-linolenic acids, 60 and 35%, respectively, with a decrease in linoleic acid, when grown in a nutrient medium consisting of B5 basal salts, sucrose or glucose, and, more importantly, at a temperature of 15°C. The application of osmotic stress employing sorbitol showed no positive influence on the fatty acid yields; furthermore, the combination of a lower culture temperature and glucose did not show a cumulative boosting effect on the yield, although this carbon source was similarly attractive. The abiotic stress also influenced the lipid profile of the cultures, significantly increasing the phosphatidylglycerol fraction but not the total lipid neither their biomass, proving the appropriateness of applying various abiotic stress in this culture to achieve larger yields.

Sample size determination for 2k-r experiments with a binomial response

Abstract This paper provides closed form expressions for the sample size for two-level factorial experiments when the response is the number of defectives. The sample sizes are obtained by approximating the two-sided test for no effect through tests for the mean of a normal distribution, and borrowing the classical sample size solution for that problem. The proposals are appraised relative to the exact sample sizes computed numerically, without appealing to any approximation to the binomial distribution, and the use of the sample size tables provided is illustrated through an example.

One-Half Fractions of a 23 Experiment for the Logistic Model

D-optimal experiments for binary response data have been extensively studied in recent years. On the other hand two-level fractional factorials are often used as screening designs at the preliminary stage of an investigation when the outcome is continuous. We explore the performance of the one-half two-level experiments for a logistic model with three factors, and show that the conventional wisdom about this kind of experiment does not apply when the response is binomial.

Fatty Acid Composition and Eicosanoid Levels (LTE4 and PGE2) of Human Milk from Normal Weight and Overweight Mothers

BACKGROUND Maternal obesity is known to affect human milk composition. Long-chain polyunsaturated fatty acids (LCPUFA) are vital nutrients to the nervous system development and precursors of eicosanoids related to obesity (prostaglandin E2-PGE2-and leukotriene E4-LTE4). The aim of the present research was to study the lipid profiles, with particular emphasis to LCPUFAs, and the concentrations of eicosanoids PGE2 and LTE4, involved in adipose tissue development, in human milk from overweight mothers compared with normal weight mothers. MATERIALS AND METHODS Study including 46 overweight and 86 normal weight breastfeeding volunteers was carried out. Fatty acids and eicosanoids (PGE2 and LTE4) were analyzed in mature human milk. Fatty acids quantification was determined by gas chromatography and mass spectrometry. PGE2 and LTE4 were measured by immununoassay. RESULTS Human milk of overweight mothers had lower contents of n-3 LCPUFA, including eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) and higher levels of total n-6 LCPUFA, compared with normal weight mothers (0.45 ± 0.23 versus 0.58 ± 0.38, p = 0.016; 0.05 ± 0.04 versus 0.08 ± 0.08, p = 0.005; 0.26 ± 0.15 versus 0.34 ± 0.22, p = 0.015; 0.84 ± 0.25 versus 0.74 ± 0.20, p = 0.029; respectively). Multiple regression analyses showed that maternal overweight was associated with human milk fatty acid profile. The levels of PGE2 and LTE4 in human milk did not show significant differences between groups. CONCLUSIONS Our findings support the hypothesis that mother weight status influences human milk n-3 LCPUFA lipid composition, but not its relationship with PGE2 and LTE4 levels.

Simulation-based designs for multiperiod control

In multiperiod control one sequentially chooses the value of an input variable to keep an output variable close to a target value. At any stage the input variable has to be such that the output is close to target while at the same time it provides as much information as possible about the model that relates input and output, to help keep the output close to target in the future. Certainty equivalence policies set the input variable at the value under which the output is estimated to be equal to target. Three alternative approaches that improve on certainty equivalence by searching for the best policy among families of policies that embed them are proposed, and their use is exemplified both on static as well as on time-varying dynamic models. Two approaches observe on credible regions for the root, while the third one is an adaptation of stochastic approximation sequences.