Mathematical models allow describing the dynamics of microbial populations under different environmental conditions. In this work, three models - Logistic, Gompertz and Baranyi-Roberts - were evaluated to characterize the growth of five beneficial bacteria present in a biological mountain soil. Model parameters were optimized using the particle swarm optimization (PSO) algorithm. Statistical analyses, based on the root mean square error (RMSE), the coefficient of determination $\left(\mathrm{R}^2\right)$, the bias factor $\left(B_f\right)$) and the precision factor $A_f$), showed that the results show that the variability between strains suggests that the choice of the optimal model may depend on the specific characteristics of each strain, however, the Logistic model proved to be the most robust and consistent, offering the best fit to the experimental data in most strains.

La presente investigación se realizó en Rio Hato, provincia de Coclé, con el objetivo de aislar e identificar microorganismos con actividad antagonista contra el patógeno fúngico Thanetophorus cucumeris (Rhizoctonia solani) en plantas de frijol (Phaseolus vulgaris), a fin de minimizar el uso de fungicidas y otros compuestos químicos utilizados en el control convencional de este hongo. Se aislaron un total de 185 bacterias y 72 hongos a partir de plantas de frijol en sus tres estados fenológicos (vegetativo, floración y fructificación) dentro de la rizósfera y filósfera. Se determinó que hubo diferencias significativas entre las diluciones utilizadas, siendo la dilución de 10-4 donde se aislaron mayor cantidad de bacterias. En relación con los organismos epífitos hubo diferencias significativas entre las diluciones, siendo la dilución 10-4 donde más bacterias se aislaron, no se determinaron diferencias entre las fases fenológicas. La fase vegetativa presentó la mayor cantidad de aislamientos; no existieron diferencias para las secciones de la filósfera. En cuanto a los hongos epifíticos no hubo diferencias estadísticas entre las diluciones ni en las fases fenológicas. En la sección endófita, la fase de fructificación presentó la mayoría de los aislamientos fúngicos. En relación con los hongos de la rizósfera se determinaron diferencias significativas en las diluciones, siendo 10-4 donde más aislamientos se obtuvo. Finalmente, se lograron aislar siete bacterias y cuatro hongos positivos con actividad biológica antagonista contra el patógeno T. cucumeris.

Se realizaron muestreos de la filósfera de arroz (variedad GAB 8), en una parcela bajo la modalidad de agricultura orgánica de subsistencia, en Los Alvéos, Coclé, Panamá. Se efectuaron aislamientos de bacterias de la filósfera del arroz, pruebas de enfrentamiento in vitro e identificación de los microorganismos bacterias con potencial antagónico frente al patógeno Burkholdería glumae que provoca añublo bacterial de la panícula del arroz. Se aislaron un total de 64 cepas bacterianas epifíticas de las cuales 24 correspondieron a la sección apical de la hoja, 11 de la sección media y 30 de la sección basal de la filósfera, de estas, 21 presentaron antagonismo positivo (halo?4mm de diámetro) ante el fitopatógeno B. glumae, se identificaron las 10 con el mayor halo de inhibición, correspondiendo al género Bacillus spp (se utilizó el sistema API y secuenciación del gen rpoB).

The objective of this study was to characterize horticultural farms in Cerro Punta, Tierras Altas (Chiriqui, Panama), on socioeconomic and agro-environmental aspects, with emphasis on the pesticides used. Thirty-one farms were randomly selected, and producers were surveyed. In addition, random soil sampling was carried out in five locations for physical-chemical and residue analysis of pesticides such as organophosphates, carbamates, pyrethroids and organochlorines. According to the results, 48% of the respondents were between 41 and 55 years of age, 39% had primary school education and 55% belonged to producer associations. The five main crops are potatoes, carrots, cabbage, lettuce, and onions, and 26% raise animals. Production costs ranged from less than USD 3500 to more than USD 14000 per hectare per year; yields ranged from 3.68 t.ha(-1) to 52.62 t.ha(-1), associated with the technologies implemented. Seventy-seven percent of the producers use untreated poultry manure, and 36 different pesticides are used in the area. Fifty-two percent use full personal protective equipment. Laboratory analyses show that the soils are of the Andisol order, with pH between 5.7 and 6.5, organic matter content between 1.34% and 4.34% and effective cation exchange capacity between 8.04 and 26.75.

The objective of this study was to characterize horticultural farms in Cerro Punta, Highlands– Chiriqui; about socioeconomic and agri-environmental aspects, with emphasis on the pesticides used, Panama. About 31 farms were randomly selected and producers were surveyed. In addition, a random soil sampling was carried out in five locations, to proceed with the physical-chemical analysis and pesticide residues analysis, such as organophosphates, carbamates, pyrethroids and organochlorines. According to the results, 48% of those surveyed are between 41 and 55 years old, with education at the primary level in 39% of cases and 55% belong to farmers associations. The five main crops are potatoes, carrots, cabbage, lettuce and onion and 26% carry out animal husbandry. The production costs were variable, from less than USD 3500 to more than USD 14 000 per hectare per year; the yield ranged from 3.68 t. ha-1 to 52.62 t. ha-1; associated with the implemented technologies. About 77% of the producers use untreated chicken manure and 36 different pesticides are used in the area. The 52% of the farmers use complete personal protective equipment. Regarding the laboratory analysis, the soils have a loamy-sandy texture, with a pH between 5.7 and 6.5, organic matter content between 1.34% and 4.34% and the Effective Cation Exchange Capacity between 8.04 and 26.75.

The gram-negative bacteriumBurkholderia Glumaeis the causal agent of the disease called bacterial panicle blight,which causes grain rot, in our case rotting of rice, which is the main crop in Panama. It was first reported in our country in2005 causing losses greater than 40 %. This study focuses onthe comparison of various nonlinear mathematical models often used to describe the growth dynamics of these kinds of bacteria and seeks to determine the best fit. The state parameters ofthese models will be optimized via the metaheuristic Particle Swarm algorithm, which is an iterative method that seeks to optimize a function, in order to select the mathematical model that allows modeling the growth of the bacteria and analysis of its characteristics, such as replication patterns, among others.

Debaryomyces hansenii is a halotolerant and Na+-includer yeast that can be isolated from different food and low-water activity products. It has also been defined as a marine-occurring yeast but key aspects for this salt tolerant behavior are far from being understood. Here, we searched for clues helping to elucidate the basis of this ability. Our results on growth, Rb+ transport, total K+ and Na+ content and vacuolar fragmentation are compatible with a yeast species adapted to cope with salt stress. On the other hand, we confirmed the existence of D. hansenii strategies that are generally observed in sensitive organisms, such as the production of glycerol as a compatible solute and the efficient vacuolar sequestration of Na+. We propose a striking role of D. hansenii vacuoles in the maintenance of constant cytosolic K+ values, even in the presence of extracellular Na+ concentration values more than two orders of magnitude higher than extracellular K+. Finally, the ability to deal with cytosolic Na+ levels significantly higher than those found in S. cerevisiae, shows the existence of important and specific salt tolerance mechanisms and determinants in D. hansenii.

The Nitrophenol compounds are used as intermediates in the production of pharmaceuticals, dyes, pesticides, wood preservatives and explosives. 2,4-dinitrophenol (2,4- DNP) is a toxic and persistent pollutant compound considered a priority by the Agency for Environmental Protection (EPA). Is selected Rhodobacter capsulatus B10S bacterial strain belonging to the group of the red photosynthetic bacteria (Rhodospirillales), this organism fotorreduce 2,4-dinitrophenol, 2-amino-4-nitrophenol (ANP) under anaerobic conditions, using a nitrophenol reductase activity which is induced in the presence of nitrophenols and repressed in cells cultured with ammonium. 2,4-DNP is an uncoupling energy that strongly inhibits nitrogen fixation in R. capsulatus. In fact, this bacteria can only grow diazotrofically (nitrogen fixation conditions) when the 2,4-DNP has become almost entirely in ANP. The aim of this study is to determine the differential expression of proteins (induction, repression, overexpression) by two-dimensional electrophoresis R. capsulatus B10S, in the presence of 2,4-DNP, in cultured cells and ammonium daizotrofic conditions. For cells grown in ammonium (RCVNH4) ammonium and more DNP (RCVNH4DNP) gels and 17 cm pH range 5-8, thirteen patches (protein) were detected, which once identified, are expected to provide information on the effect of the consumption of ammonium 2,4-DNP, regulating their transport into the cell, expression of gene (s) of nitroreductase (s), nitroreductase activity and the electron donor (s) nitroreductase (s).

Saccharomyces cerevisiae mutants lacking both isoforms of the main plasma membrane potassium transporter display impaired potassium transport and defective growth at limiting concentrations of the cation. Moreover, they are hyperpolarized and have a lower intracellular pH than wild-type. In order to unravel global physiological processes altered in trk1,2 mutants, we have established conditions at which both wild-type and mutants can grow at different rates. Using a combination of physiological, biochemical and proteomic approaches, we show that during growth at suboptimal potassium concentrations, double trk1,2 mutants accumulate less potassium and reach lower yields. In contrast, the mutants maintain increased viability in the stationary phase and retain more potassium. Moreover, the mutants show increased expression of stress-related proteins such as catalase T, thioredoxin peroxidase or hexokinase 2, suggesting that they are better adapted to the additional stress factors associated with entry into stationary growth phase.

Living cells accumulate potassium (K+) to fulfil multiple functions. It is well documented that the model yeast Saccharomyces cerevisiae grows at very different concentrations of external alkali cations and keeps high and low intracellular concentrations of K+ and sodium (Na+) respectively. However less attention has been paid to the study of the intracellular distribution of these cations. The most widely used experimental approach, plasma membrane permeabilization, produces incomplete results, since it usually considers only cytoplasm and vacuoles as compartments where the cations are present in significant amounts. By isolating and analysing the main yeast organelles, we have determined the subcellular location of K+ and Na+ in S. cerevisiae. We show that while vacuoles accumulate most of the intracellular K+ and Na+, the cytosol contains relatively low amounts, which is especially relevant in the case of Na+. However K+ concentrations in the cytosol are kept rather constant during the K+-starvation process and we conclude that, for that purpose, vacuolar K+ has to be rapidly mobilized. We also show that this intracellular distribution is altered in four different mutants with impaired vacuolar physiology. Finally, we show that both in wild-type and vacuolar mutants, nuclei contain and keep a relatively constant and important percentage of total intracellular K+ and Na+, which most probably is involved in the neutralization of negative charges.

Saccharomyces cerevisiae cells are able to grow at very different potassium concentrations adapting its intracellular cation levels to changes in the external milieu. Potassium homeostasis in wild type cells resuspended in media with low potassium is an example of non-perfect adaptation since the same intracellular concentration is not approached irrespective of the extracellular levels of the cation. By using yeasts lacking the Trk1,2 system or expressing different versions of the mutated main plasma membrane potassium transporter (Trk1), we show that Trk1 is not essential for adaptation to potassium changes but the dynamics of potassium loss is very different in the wild type and in trk1,2 mutant or in yeasts expressing Trk1 versions with highly impaired transport characteristics. We also show that the pattern here described can be also fulfilled by heterologous expression of NcHAK1, a potassium transporter not belonging to the TRK family. Hyperpolarization and cationic drugs sensitivity in mutants with defective transport capacity provide additional support to the hypothesis of connections between the activity of the Trk system and the plasma membrane H(+) ATPase (Pma1) in the adaptive process.

The intrinsic ability of cells to adapt to a wide range of environmental conditions is a fundamental process required for survival. Potassium is the most abundant cation in living cells and is required for essential cellular processes, including the regulation of cell volume, pH and protein synthesis. Yeast cells can grow from low micromolar to molar potassium concentrations and utilize sophisticated control mechanisms to keep the internal potassium concentration in a viable range. We developed a mathematical model for Saccharomyces cerevisiae to explore the complex interplay between biophysical forces and molecular regulation facilitating potassium homeostasis. By using a novel inference method ("the reverse tracking algorithm") we predicted and then verified experimentally that the main regulators under conditions of potassium starvation are proton fluxes responding to changes of potassium concentrations. In contrast to the prevailing view, we show that regulation of the main potassium transport systems (Trk1,2 and Nha1) in the plasma membrane is not sufficient to achieve homeostasis.

ABSTRACT Potassium homeostasis is crucial for living cells. In the yeast Saccharomyces cerevisiae , the uptake of potassium is driven by the electrochemical gradient generated by the Pma1 H + -ATPase, and this process represents a major consumer of the gradient. We considered that any mutation resulting in an alteration of the electrochemical gradient could give rise to anomalous sensitivity to any cationic drug independently of its toxicity mechanism. Here, we describe a genomewide screen for mutants that present altered tolerance to hygromycin B, spermine, and tetramethylammonium. Two hundred twenty-six mutant strains displayed altered tolerance to all three drugs (202 hypersensitive and 24 hypertolerant), and more than 50% presented a strong or moderate growth defect at a limiting potassium concentration (1 mM). Functional groups such as protein kinases and phosphatases, intracellular trafficking, transcription, or cell cycle and DNA processing were enriched. Essentially, our screen has identified a substantial number of genes that were not previously described to play a direct or indirect role in potassium homeostasis. A subset of 27 representative mutants were selected and subjected to diverse biochemical tests that, in some cases, allowed us to postulate the basis for the observed phenotypes.

To estimate the prevalence of antibodies to human immunodeficiency virus (HIV), antibodies to hepatitis B core antigen (anti-HBc), hepatitis B surface antigen (HBsAg), and antibodies to delta virus (anti-DV).Cross-sectional (prevalence) study. A non-proportional (stratified by length of stay) random sample of 20% of admitted patients was selected.The Hospital Psiquiátrico Nuestra Señora de Montserrat (Sant Boi de Llobregat, Barcelona, Spain) admits about 670 patients in its short-term, rehabilitation (mid-term) and long-term wards.139 patients were selected: 91% were males, mean age was 55 years, and 10% belonged to an HIV risk group; mean length of hospitalization since last discharge was 13 years.Blood samples were drawn in October, 1988. Anti-HBc, HBsAg and anti-DV were determined by competitive enzyme immunoassay (EIA). Anti-HIV-1 were determined by sandwich EIA; negativity of results with high absorbency but below the cut-off point was confirmed by Western blot.None of the sampled patients had circulating anti-HIV-1 antibodies. Four cases showing high absorbency (below the "cut-off" point) were ruled out by Western-blot. Overall, the prevalence of anti-HBc was 52.8% (54.4% in long-term wards, 35.0% in mid-term wards, and 13.8% in short-term wards). The prevalence of HBsAg was 2.3%, of anti-DV 1.5%, and of HDAg 0%.Prevalence of anti-HIV is null in the studied institution. Current efforts to prevent HIV infection must continue; a hepatitis B vaccination program is highly warranted among patients and professionals of the studied hospital.

OBJECTIVES:To estimate the prevalence of antibodies to human immunodeficiency virus (HIV), antibodies to hepatitis B core antigen (anti-HBc), hepatitis B surface antigen (HBsAg), and antibodies to delta virus (anti-DV).DESIGN:Cross-sectional (prevalence) study. A non-proportional (stratified by length of stay) random sample of 20% of admitted patients was selected.CLINICAL SETTING:The Hospital Psiquiátrico Nuestra Señora de Montserrat (Sant Boi de Llobregat, Barcelona, Spain) admits about 670 patients in its short-term, rehabilitation (mid-term) and long-term wards.SUBJECTS:139 patients were selected: 91% were males, mean age was 55 years, and 10% belonged to an HIV risk group; mean length of hospitalization since last discharge was 13 years.MEASUREMENTS:Blood samples were drawn in October, 1988. Anti-HBc, HBsAg and anti-DV were determined by competitive enzyme immunoassay (EIA). Anti-HIV-1 were determined by sandwich EIA; negativity of results with high absorbency but below the cut-off point was confirmed by Western blot.RESULTS:None of the sampled patients had circulating anti-HIV-1 antibodies. Four cases showing high absorbency (below the "cut-off" point) were ruled out by Western-blot. Overall, the prevalence of anti-HBc was 52.8% (54.4% in long-term wards, 35.0% in mid-term wards, and 13.8% in short-term wards). The prevalence of HBsAg was 2.3%, of anti-DV 1.5%, and of HDAg 0%.CONCLUSIONS:Prevalence of anti-HIV is null in the studied institution. Current efforts to prevent HIV infection must continue; a hepatitis B vaccination program is highly warranted among patients and professionals of the studied hospital.