pH Of Growth Medium Research Articles

Aminoglycoside inhibition of Staphylococcus aureus biofilm formation is nutrient dependent

Biofilms represent microbial communities, encased in a self-produced matrix or extracellular polymeric substance. Microbial biofilms are likely responsible for a large proportion of clinically significant infections and the multicellular nature of biofilm existence has been repeatedly associated with antibiotic resistance. Classical in vitro antibiotic-susceptibility testing utilizes artificial growth media and planktonic microbes, but this method may not account for the variability inherent in environments subject to biofilm growth in vivo. Experiments were designed to test the hypothesis that nutrient concentration can modulate the antibiotic susceptibility of Staphylococcus aureus biofilms. Developing S. aureus biofilms initiated on surgical sutures, and in selected experiments planktonic cultures, were incubated for 16 h in 66 % tryptic soy broth, 0.2 % glucose (1× TSBg), supplemented with bactericidal concentrations of gentamicin, streptomycin, ampicillin or vancomycin. In parallel experiments, antibiotics were added to growth medium diluted one-third (1/3× TSBg) or concentrated threefold (3× TSBg). Following incubation, viable bacteria were enumerated from planktonic cultures or suture sonicates, and biofilm biomass was assayed using spectrophotometry. Interestingly, bactericidal concentrations of gentamicin (5 µg gentamicin ml(-1)) and streptomycin (32 µg streptomycin ml(-1)) inhibited biofilm formation in samples incubated in 1/3× or 1× TSBg, but not in samples incubated in 3× TSBg. The nutrient dependence of aminoglycoside susceptibility is not only associated with biofilm formation, as planktonic cultures incubated in 3× TSBg in the presence of gentamicin also showed antibiotic resistance. These findings appeared specific for aminoglycosides because biofilm formation was inhibited in all three growth media supplemented with bactericidal concentrations of the cell wall-active antibiotics, ampicillin and vancomycin. Additional experiments showed that the ability of 3× TSBg to overcome the antibacterial effects of gentamicin was associated with decreased uptake of gentamicin by S. aureus. Uptake is known to be decreased at low pH, and the kinetic change in pH of growth medium from biofilms incubated in 5 µg gentamicin ml(-1) in the presence of 3× TSBg was decreased when compared with pH determinations from biofilms formed in 1/3× or 1× TSBg. These studies underscore the importance of environmental factors, including nutrient concentration and pH, on the antibiotic susceptibility of S. aureus planktonic and biofilm bacteria.

Engineering Hydrogen Gas Production from Formate in a Hyperthermophile by Heterologous Production of an 18-Subunit Membrane-bound Complex

Biohydrogen gas has enormous potential as a source of reductant for the microbial production of biofuels, but its low solubility and poor gas mass transfer rates are limiting factors. These limitations could be circumvented by engineering biofuel production in microorganisms that are also capable of generating H2 from highly soluble chemicals such as formate, which can function as an electron donor. Herein, the model hyperthermophile, Pyrococcus furiosus, which grows optimally near 100 °C by fermenting sugars to produce H2, has been engineered to also efficiently convert formate to H2. Using a bacterial artificial chromosome vector, the 16.9-kb 18-gene cluster encoding the membrane-bound, respiratory formate hydrogen lyase complex of Thermococcus onnurineus was inserted into the P. furiosus chromosome and expressed as a functional unit. This enabled P. furiosus to utilize formate as well as sugars as an H2 source and to do so at both 80° and 95 °C, near the optimum growth temperature of the donor (T. onnurineus) and engineered host (P. furiosus), respectively. This accomplishment also demonstrates the versatility of P. furiosus for metabolic engineering applications.

Harvesting Nannochloropsis oculata by Flocculation

<abstract><title><italic>Abstract.</italic></title> Algal biomass harvesting from dilute suspensions of a culture is challenging. Although a flocculation process is commonly used to separate suspended solids from water, information on the flocculation characteristics of microalgae cells is limited. In this study, the flocculation characteristics of Nannochloropsis oculata (NO) were examined. Chitosan addition, adjustment of the pH of the growth medium, and electroflocculation techniques were examined. Adjustment of the algae growth medium pH to 11 resulted in over 99% flocculation efficiency. Although chitosan addition facilitated cell flocculation at a lower pH (pH 9), the high flocculant requirement is a disadvantage of this process. In general, the efficiency of electroflocculation improved with increasing current, operation time (OT), and settling time (ST), and 97.1% NO cell flocculation efficiency could be obtained at 0.3 A, 3 min OT, and 30 min ST. This study demonstrated that over 90% NO cell flocculation efficiency is achievable by adjusting the pH of the growth medium, chitosan addition, or electroflocculation. The process selection for commercial operations needs to be based on the characteristics of the harvested biomass required for a given application and the environmental impact and economic feasibility of the process.

Carbonic anhydrase: a key regulatory and detoxifying enzyme for Karst plants

Karstification is a rapid process during which calcidic stones/limestones undergo dissolution with the consequence of a desertification of karst regions. A slow-down of those dissolution processes of Ca-carbonate can be approached by a reforestation program using karst-resistant plants that can resist alkaline pH and higher bicarbonate (HCO₃⁻) concentrations in the soil. Carbonic anhydrases (CA) are enzymes that mediate a rapid and reversible interconversion of CO₂ and HCO₃⁻. In the present study, the steady-state expression of a CA gene, encoding for the plant carbonic anhydrase from the parsley Petroselinum crispum, is monitored. The studies were primarily been performed during germination of the seeds up to the 12/14-day-old embryos. The CA cDNA was cloned. Quantitative polymerase chain reaction (qPCR) analysis revealed that the gene expression level of the P. crispum CA is strongly and significantly affected at more alkaline pH in the growth medium (pH 8.3). This abolishing effect is counteracted both by addition of HCO₃⁻ and by addition of polyphosphate (polyP) to the culture medium. In response to polyP, the increased pH in the vacuoles of the growing plants is normalized. The effect of polyP let us to propose that this polymer acts as a buffer system that facilitates the adjustment of the pH in the cytoplasm. In addition, it is proposed that polyP has the potential to act, especially in the karst, as a fertilizer that allows the karstic plants to cope with the adverse pH and HCO₃⁻ condition in the soil.

A natural plant growth promoter, calliterpenone, enhances growth and biomass, carbohydrate, and lipid production in cyanobacterium Synechocystis PCC 6803

Cyanobacteria have evolved photosynthetic mechanisms in which solar energy is used to fix CO2 into carbohydrates. The lipids from cyanobacteria can be converted to biodiesel by extraction–transesterification methods. The present study demonstrates the usefulness of the natural plant and microbial growth promoter calliterpenone from the plant Callicarpa macrophylla supplemented at three different doses (15, 25, 50 μL of a 0.01 mM solution) per 100 mL BG11+ medium for enhancing total biomass, carbohydrate, and lipid yields and reducing the surface-to-volume ratios of cells of Synechocystis PCC 6803. The enhanced total dried biomass, carbohydrate, and lipid production was 316.1, 140.34, and 130.76 %, respectively, higher than the control, and were obtained after 15 days of cultivation at the dose of 15 μL (0.01 mM) of calliterpenone per 100 mL BG11+ medium. A decrease in surface-to-volume ratio of cells from 1.19 to 0.84 compared to the control was also observed. Response surface methodology was used to optimize the doses of calliterpenone at different pH of growth media. An increase of 346.95, 187.2, and 134.46 % in biomass, carbohydrate, and lipid yields, respectively, was achieved after 10 days of cultivation in optimized BG11+ media at pH 7.5 and with 20 μL (0.01 mM) calliterpenone per 100 mL. Thus, this biomolecule can be exploited for higher yields of Synechocystis PCC 6803 in a relatively shorter culture time making this an attractive strategy for fuel production using this cyanobacterium.

Alteration of Plasma Membrane Organization by an Anticancer Lysophosphatidylcholine Analogue Induces Intracellular Acidification and Internalization of Plasma Membrane Transporters in Yeast

The lysophosphatidylcholine analogue edelfosine is a potent antitumor lipid that targets cellular membranes. The underlying mechanisms leading to cell death remain controversial, although two cellular membranes have emerged as primary targets of edelfosine, the plasma membrane (PM) and the endoplasmic reticulum. In an effort to identify conditions that enhance or prevent the cytotoxic effect of edelfosine, we have conducted genome-wide surveys of edelfosine sensitivity and resistance in Saccharomyces cerevisiae presented in this work and the accompanying paper (Cuesta-Marbán, Á., Botet, J., Czyz, O., Cacharro, L. M., Gajate, C., Hornillos, V., Delgado, J., Zhang, H., Amat-Guerri, F., Acuña, A. U., McMaster, C. R., Revuelta, J. L., Zaremberg, V., and Mollinedo, F. (January 23, 2013) J. Biol. Chem. 288,), respectively. Our results point to maintenance of pH homeostasis as a major player in modulating susceptibility to edelfosine with the PM proton pump Pma1p playing a main role. We demonstrate that edelfosine alters PM organization and induces intracellular acidification. Significantly, we show that edelfosine selectively reduces lateral segregation of PM proteins like Pma1p and nutrient H(+)-symporters inducing their ubiquitination and internalization. The biology associated to the mode of action of edelfosine we have unveiled includes selective modification of lipid raft integrity altering pH homeostasis, which in turn regulates cell growth.

Organic acids are not specifically involved in the nitrate-enhanced Zn hyperaccumulation mechanism in Noccaea caerulescens

Nitrogen form has been shown to affect Zn uptake, translocation and storage in the Zn-hyperaccumulating plant Noccaea caerulescens but the biochemical processes are not fully understood. Organic acids and amino acids have been implicated in Zn transport and storage. This study aimed to examine the effect of N form on concentrations of organic acids and amino acids and how these metabolites correlated with Zn hyperaccumulation. Plants were grown in nutrient solution with NO3−, NH4NO3 or NH4+, supplied with 50 or 300μM Zn, and buffered at either pH 4.5 or 6.5. The metabolomic profile was determined by gas chromatography mass spectroscopy. The concentration of Zn in shoots, xylem and roots was greatest for the NO3−, pH 6.5 and 300μM Zn treatments. For all N forms, the lower growth-medium pH raised xylem sap pH but had no influence on Zn concentration or exudation rate of the xylem sap. Nitrate enhanced organic acid production while NH4+ increased amino acid production. Organic acids in the xylem were more responsive to changes in growth-medium pH than N form, and did not correlate with Zn concentration in shoots, roots or xylem. Serine might be directly involved in Zn hyperaccumulation. Phosphoric acid was associated with reduced Zn accumulation in the shoots. Malic acid was not detected in the shoots but responded to cation uptake more than to Zn specifically in the roots. Citric acid responded to cation uptake more than to Zn specifically in the shoots but did not correlate with Zn concentration in the roots or the xylem sap, or any other cations in the roots. In conclusion, organic acids in N. caerulescens are not specifically involved in Zn hyperaccumulation but are involved in regulating pH in the xylem and cation–anion balance in plants.

Effect of Growth Media, pH and Temperature on Yeast to Hyphal Transition in &amp;lt;i&amp;gt;Candida albicans&amp;lt;/i&amp;gt;

The transition of C. albicans from unicellular yeast form to filamentous form i.e., pseudohyphae and hyphae is referred to as morphogenesis. C. albicans has the ability to respond to environmental conditions and accordingly changing its cell morphology. Three main morphological forms of C. albicans are unicellular yeast, pseudohyphae and hyphae. The effect of different growth media (Horse serum medium, RPMI-1640, MSGB), incubation temperatures (34°C, 37°C, 40°C) and pH values (5.4, 6.4, 7.4) on germ tube production by C. albicans was evaluated. Horse serum medium noticeably promotes filamentation while RPMI-1640 medium shows moderate filamentation and MSGB media shows moderately low filamentation. The germ tube of C. albicans developed early in 1.5 hr at high temperature i.e., 40°C. Incubation temperature of 37°C was associated with highest germ tube formation while 34°C shows low filamentation. A pH of 5.4 also induces low filamentation, pH 6.4 gives moderately lower than pH 7.4. A pH of 7.4 was best suited for germ tube induction. The peak of mycelium production appears between 1.5 and 6 hr after inoculation of C. albicans culture. These results suggested that environmental factors are important in selectively favoring yeast or hyphal form, most important being the growth medium, incubation temperature and external pH value.

Efficiency of neural network-based combinatorial model predicting optimal culture conditions for maximum biomass yields in hairy root cultures

KEY MESSAGE : ANN-based combinatorial model is proposed and its efficiency is assessed for the prediction of optimal culture conditions to achieve maximum productivity in a bioprocess in terms of high biomass. A neural network approach is utilized in combination with Hidden Markov concept to assess the optimal values of different environmental factors that result in maximum biomass productivity of cultured tissues after definite culture duration. Five hidden Markov models (HMMs) were derived for five test culture conditions, i.e. pH of liquid growth medium, volume of medium per culture vessel, sucrose concentration (%w/v) in growth medium, nitrate concentration (g/l) in the medium and finally the density of initial inoculum (g fresh weight) per culture vessel and their corresponding fresh weight biomass. The artificial neural network (ANN) model was represented as the function of these five Markov models, and the overall simulation of fresh weight biomass was done with this combinatorial ANN-HMM. The empirical results of Rauwolfia serpentina hairy roots were taken as model and compared with simulated results obtained from pure ANN and ANN-HMMs. The stochastic testing and Cronbach's α-value of pure and combinatorial model revealed more internal consistency and skewed character (0.4635) in histogram of ANN-HMM compared to pure ANN (0.3804). The simulated results for optimal conditions of maximum fresh weight production obtained from ANN-HMM and ANN model closely resemble the experimentally optimized culture conditions based on which highest fresh weight was obtained. However, only 2.99% deviation from the experimental values could be observed in the values obtained from combinatorial model when compared to the pure ANN model (5.44%). This comparison showed 45% better potential of combinatorial model for the prediction of optimal culture conditions for the best growth of hairy root cultures.

Escherichia coli Growth Changes by the Mediated Effects After Low-Intensity Electromagnetic Irradiation of Extremely High Frequencies

Water is the major constituent of environmental medium and biological systems. The effects occurring in water as a result of low-intensity electromagnetic irradiation (EMI) in extremely high frequencies are supposed to be the primary mechanism to create conditions for biological responses. The EMI effects on Escherichia coli, after irradiation of their suspension, are most probably water-mediated. Indirect effects of EMI at 51.8, 53, 70.6, and 73GHz frequencies on bacteria, through water, assay buffer (Tris-phosphate buffer with inorganic salts at low or moderate concentrations), or peptone growth medium were studied. The mediated effects of 70.6 and 73GHz irradiated water, assay buffer, and growth medium on E. coli growth characteristics were insignificant. But the results were different for 51.8 and 53GHz. EMI mediated effects on bacterial growth were clearly demonstrated. The effects were more strongly expressed with 53GHz. Moreover, it was shown that 70.6 and 73GHz similarly suppressed the cell growth after direct irradiation of E. coli in water or on solid medium. Interestingly, for 51.8 and 53GHz the bacterial growth decreases after suspension irradiation was less, compared to the direct irradiation of bacteria on solid medium. Especially, it was also more expressed in case of 53GHz. Also with electron microscopy, EMI-induced bacterial cell sizes and structure different changes were detected. In addition, the distinguished changes in surface tension, oxidation-reduction potential and pH of water, assay buffer, growth medium, and bacterial suspension were determined. They depended on EMI frequency used. The differences could be associated with the partial absorbance of EMI energy by the surrounding medium, which depends on a specific frequency. The results are crucial to understand biophysical mechanisms of EMI effects on bacteria.

Validation of Fermentative Parameters for Efficient Succinate Production in Batch Operation by &lt;i&gt;Actinobacillus succinogenes&lt;/i&gt; 130ZT

Succinate is an important platform molecule in the synthesis of a number of commodity and specialty chemicals. In the present study, the effects of different carbon and nitrogen sources, initial pH of the growth medium (pH 4.5-9.0), and temperature (25-45°C) on the fermentative succinate production by Actinobacillus succinogenes 130ZT were investigated in 100 mL anaerobic bottles. The results revealed that the highest concentration of succinate at 6.28 g/L was produced from 10 g/L of glucose or lactose in the medium containing 5 g/L yeast extract at 24 h. However, a comparable concentration of succinate was also produced when the medium was supplemented with 5 g/L spent brewer’s yeast extract. Based on these results, the cost effectiveness of succinate production could be improved by the use of glucose or lactose fermentation supplemented with spent brewer’s yeast extract. Optimized initial pH at 8.0, temperature at 37 °C, and inoculum size at 6% (v/v) provided the best succinate production at the concentration of 6.37 g/L with a yield of 68.73%.

High external pH enables more efficient secretion of alkaline α-amylase AmyK38 by Bacillus subtilis

BackgroundBacillus subtilis genome-reduced strain MGB874 exhibits enhanced production of exogenous extracellular alkaline cellulase Egl-237 and subtilisin-like alkaline protease M-protease. Here, we investigated the suitability of strain MGB874 for the production of α-amylase, which was anticipated to provoke secretion stress responses involving the CssRS (Control secretion stress Regulator and Sensor) system.ResultsCompared to wild-type strain 168, the production of a novel alkaline α-amylase, AmyK38, was severely decreased in strain MGB874 and higher secretion stress responses were also induced. Genetic analyses revealed that these phenomena were attributable to the decreased pH of growth medium as a result of the lowered expression of rocG, encoding glutamate dehydrogenase, whose activity leads to NH3 production. Notably, in both the genome-reduced and wild-type strains, an up-shift of the external pH by the addition of an alkaline solution improved AmyK38 production, which was associated with alleviation of the secretion stress response. These results suggest that the optimal external pH for the secretion of AmyK38 is higher than the typical external pH of growth medium used to culture B. subtilis. Under controlled pH conditions, the highest production level (1.08 g l-1) of AmyK38 was obtained using strain MGB874.ConclusionsWe demonstrated for the first time that RocG is an important factor for secretory enzyme production in B. subtilis through its role in preventing acidification of the growth medium. As expected, a higher external pH enabled a more efficient secretion of the alkaline α-amylase AmyK38 in B. subtilis. Under controlled pH conditions, the reduced-genome strain MGB874 was demonstrated to be a beneficial host for the production of AmyK38.

Study the ability of some local algae tolerance to some heavy metals

In this study Three genera of common algae isolated from local environment in Mosul city were tested for their ability to utilize heavy metals Oscillatoria angustissima, Fragellaria vaucheria and Lyngbya tylorii were isolated and grown under effect of five different concentrations of heavy metals cupper chloride CuCl2, cobalt chloride CoCl2 and nickel chloride NiCl2, and assayed for the rate of daily growth, biomass and final pH of growth medium after fifteenth days of incubation. The results showed, that the highest growth of algae was achieved at zero concentration for all treatments, while there was adecrease in growth rate and biomass production with increase of the concentration of heavy metals which were used in the experiments. All algal genera revealed tolerant capability in high concentration of heavy metals relatively. The results also showed, that Oscillatoria angustissima could tolerate high concentration especially nikel and the growth rate could not be affected sharply with high concentration of nikel in the growth medium.

The Effect of Growth Medium pH towards Trypsin-Like Activity Produced by Lactic Acid Bacteria

In cases of pancreatic disease, trypsin deficiency often occurs due to reduced expression of trypsin in the pancreas. Patients with pancreatic problem can be treated with a supplement containing digestive enzymes, including trypsin. However, most of the enzymes currently used for the treatment are derived from porcine and bovine sources. On the other hand, lactic acid bacteria are also known to show trypsin-like activity. In the previous work, our group screened 11 lactic acid bacteria isolates, which had previously been proven to show serine protease activity, for trypsin-like activity. The strains were initially grown in MRS (de Mann, Rogosa and Sharpe) medium before being transferred directly to the production medium to produce trypsin. During the previous study, the initial pH of the production medium was set at 6 (the same as the MRS medium pH), which is the optimum pH for the cell growth of lactic acid bacteria. However, most trypsin has an optimum pH of around 8. In this study, we altered the production medium pH to 8 and we harvested the lactic acid bacteria from MRS medium by centrifugation prior to their inoculation to the production medium. Observation of the culture growth and enzyme activity indicated that the new strategy improved the enzyme activity expressed by some strains.

Antibacterial and physical properties of calcium–phosphate and calcium–fluoride nanocomposites with chlorhexidine

ObjectivesPrevious studies have developed calcium phosphate and fluoride releasing composites. Other studies have incorporated chlorhexidine (CHX) particles into dental composites. However, CHX has not been incorporated in calcium phosphate and fluoride composites. The objectives of this study were to develop nanocomposites containing amorphous calcium phosphate (ACP) or calcium fluoride (CaF2) nanoparticles and CHX particles, and investigate Streptococcus mutans biofilm formation and lactic acid production for the first time. MethodsChlorhexidine was frozen via liquid nitrogen and ground to obtain a particle size of 0.62μm. Four nanocomposites were fabricated with fillers of: nano ACP; nano ACP+10% CHX; nano CaF2; nano CaF2+10% CHX. Three commercial materials were tested as controls: a resin-modified glass ionomer, and two composites. S. mutans live/dead assay, colony-forming unit (CFU) counts, biofilm metabolic activity, and lactic acid were measured. ResultsAdding CHX fillers to ACP and CaF2 nanocomposites greatly increased their antimicrobial capability. ACP and CaF2 nanocomposites with CHX that were inoculated with S. mutans had a growth medium pH>6.5 after 3 d, while the control commercial composites had a cariogenic pH of 4.2. Nanocomposites with CHX reduced the biofilm metabolic activity by 10–20 folds and reduced the acid production, compared to the controls. CFU on nanocomposites with CHX were three orders of magnitude less than that on commercial composite. Mechanical properties of nanocomposites with CHX matched a commercial composite without fluoride. SignificanceThe novel calcium phosphate and fluoride nanocomposites could be rendered antibacterial with CHX to greatly reduce biofilm formation, acid production, CFU and metabolic activity. The antimicrobial and remineralizing nanocomposites with good mechanical properties may be promising for a wide range of tooth restorations with anti-caries capabilities.

Study on Shrimp Waste Water and Vermicompost as a Nutrient Source for Bell Peppers

The aquaculture industry generates significant nutrient-rich wastewater that is released into streams and rivers causing environmental concern. The objective of this controlled environment study was to evaluate the effect of waste shrimp water (SW), vermicompost (VC), at rates of 10%, 20%, 40%, and 80% by volume alone or in combination with SW, controlled-release fertilizer (CRF), and water-soluble fertilizer (WSF) on bell peppers (Capsicum annuum L.) cv. X3R Red Knight. Application of VC at 80% or SW alone increased yields relative to unfertilized control. Combined applications of VC and SW increased yields compared with VC alone. Overall, total yields were greatest in the chemical fertilizer treatments (CRF and WSF) and least in the unfertilized control. SW and VC increased growth medium pH relative to the unfertilized control or to the chemical fertilizer treatments. In pepper fruits, the greatest nitrogen (N) content was found in the CRF treatment, although it was not different from VC at high rates or WSF treatments. Phosphorus concentration in peppers was greatest in the CRF treatment, less in all VC or SW treatments, but not different from unfertilized control or WSF treatment. Iron, magnesium (Mg), and zinc concentrations in peppers were greatest in CRF treatment but not different from control or WSF treatments. Overall, N accumulation in peppers was negatively correlated to growth medium pH and calcium (Ca); phosphorus (P) in peppers was negatively correlated to growth medium pH, Ca, and sodium (Na), whereas potassium (K) in peppers was negatively correlated to growth medium P, Mg, and Na. Results indicated: 1) SW may not be a viable pepper nutrient source; (2) SW can provide a similar nutrient supply as VC; and (3) chemical fertilizers can provide higher pepper yields compared with SW or VC alone or in combination.

EVALUATION OF THE PERFORMANCE OF BACILLUS CEREUS FOR ASSAY OF TETRACYCLINES IN CHICKEN MEAT

ABSTRACTIn the Kenyan poultry industry, there is lack of affordable and easy‐to‐perform antibiotic residue screening methods. The aim of this study was to determine the limits of detection (LODs) of oxytetracycline (OTC) and evaluate whether it is reliably detectable at maximum residue limits (MRLs) in poultry tissues. Microbiological detection was achieved by agar well diffusion using Bacillus cereus, three medium pH and two poultry organs. Inhibition zones increased significantly (P &lt; 0.001) when OTC was detected at a decreasing pH in both the liver and the kidney. OTC was detected below the MRLs of 600 ng/g in the liver and 1,200 ng/g in the kidney. However, growth media pH and antibiotic concentration affected the LODs. B. cereus plate at pH 7 can be used effectively for routine screening for OTC residues. The LODs were 131.3 ng/mL and 33.4 ng/mL, in the liver and the kidney, respectively.PRACTICAL APPLICATIONSApproximately 14.6 tons of active antibiotics are annually used in food animal production in Kenya. Most of the methods for screening of veterinary drugs in animal products are expensive. This is one of the factors that has contributed to the failure of observance of regulations regarding antibiotic residues in most developing countries. The described method can screen for residues of drugs in chicken meat inexpensively, quickly and with ease. This forms a basis for wider adaptability in the developing world so that unsafe samples can be selected from a majority of samples that do not contain drug residues for further quantitative testing.

A neural network approach for the prediction of in vitro culture parameters for maximum biomass yields in hairy root cultures

The present study deals with ANN based prediction of culture parameters in terms of inoculum density, pH and volume of growth medium per culture vessel and sucrose content of the growth medium for Glycyrrhiza hairy root cultures. This kind of study could be a model system in exploitation of hairy root cultures for commercial production of pharmaceutical compounds using large bioreactors. The study is aimed to evaluate the efficiency of regression neural network and back propagation neural network for the prediction of optimal culture conditions for maximum hairy root biomass yield. The training data for regression and back propagation networks were primed on the basis of function approximation, where final biomass fresh weight ( f wt ) was considered as a function of culture parameters. On this basis the variables in culture conditions were described in the form of equations which are for inoculum density: y=0.02 x+0.04, for pH of growth medium: y= x+2.8, for sucrose content in medium: y=9.9464 x+(−9.7143) and for culture medium per culture vessel: y=10 x. The fresh weight values obtained from training data were considered as target values and further compared with predicted fresh weight values. The empirical data were used as testing data and further compared with values predicted from trained networks. Standard MATLAB inbuilt generalized regression network with radial basis function radbas as transfer function in layer one and purelin in layer two and back propagation having purelin as transfer function in output layer and logsig in hidden layer were used. Although in comparative assessment both the networks were found efficient for prediction of optimal culture conditions for high biomass production, more accuracy in results was seen with regression network.

Microbiological analysis of some vended sachet water in Ogbomoso, Nigeria

Water borne bacterial pathogens were isolated from sachet water vended in Ogbomoso, Oyo State, Nigeria. The isolates were characterized and identified as Bacillus subtilis, Bacillus alvei, Pseudomonas putida, Pseudomonas fluorescens, Bacillus cereus, Enterobacter aerogenes and Proteus mirabilis. The antibiotic susceptibility profile of the seven isolates was determined and it was discovered that 59.3% was found sensitive to the commercial antibiotic disc used while 40.7% was resistant. The effect of temperature, pH and sodium chloride concentration on the growth rate of isolates was investigated. It was found that as temperature of incubation increased from 50 to 80°C, the rate of growth of all the isolate decreased and as the pH of the growth medium increased from 3 to 9, the rate of growth of all the isolates also increased. As the concentration of sodium chloride increased from 2 to 5%, the rate of growth of isolates also reduced. Key words: Bacillus subtilis, Bacillus alvei, Pseudomonas putida, Pseudomonas fluorescens, Bacillus cereus, Enterobacter aerogenes and Proteus mirabilis,sachet water, pH, temperature and sodium chloride.

In vitro characterization of Inocutis jamaicensis and experimental inoculation of Eucalyptus globulus standing trees

SummaryLesions of variable size, associated with the hymenomycete Inocutis jamaicensis, a white‐rot fungus, have been observed on the stems of Eucalyptus globulus trees in Uruguay. The aim of this study was to evaluate some ecophysiological characteristics of I. jamaicensis and assess its ability to colonize E. globulus trees of two different seed origins (Geeveston and Jeeralang) and the clone, 334‐1‐AR, obtained by micropropagation (ENCE, Spain). The growth of an I. jamaicensis isolate (MVHC11379) was evaluated at 25°C in a medium with a water potential of 0 (Ψ = 0). The growth rate did not vary significantly with a growth medium pH of between 4 and 7. I. jamaicensis showed no growth at either 5 or 37°C at any pH or Ψ tested. Weight loss of heartwood and sapwood of different plant provenances inoculated with I. jamaicensis under laboratory conditions was evaluated, and significant differences observed. Lignin‐modifying enzyme activity was evaluated in culture medium with or without E. globulus sawdust as substrate or inducer. Laccase activity was observed with sawdust and manganese peroxidase activity with and without sawdust. Only slight activity of aryl‐alcohol oxidase and lignin peroxidase was detected without sawdust. Experimental inoculation with I. jamaicensis of 3‐year‐old Geeveston and Jeeralang, and of 4‐year‐old 334‐1‐AR stems, resulted in successful fungal colonization of 56% of the 334‐1‐AR, 50% of Geeveston and 25% of Jeeralang trees. Only the heartwood was decayed. In 334‐1‐AR, the rotted wood was delimited by a reaction zone. Wood characteristics and the ability of I. jamaicensis to overcome the chemical reactions in the tree could partially explain differences in susceptibility to the fungus among provenances observed under natural and laboratory conditions.