Bacterial Adhesion To Hydrocarbons Research Articles

Biosurfactant, polythene, plastic, and diesel biodegradation activity of endophytic Nocardiopsis sp. mrinalini9 isolated from Hibiscus rosasinensis leaves

Endophytic non-streptomycetes group of actinomycetes from Hibiscus rosasinensis leaves were screened for biosurfactant, polythene, plastic, and diesel biodegradation activities. Biosurfactant activity was evaluated by hemolysis, drop-collapsing test, lipase production, oil-spreading technique, bacterial adhesion to hydrocarbon (BATH) assay, penetration assay, and emulsification assay. Similarly, polythene, plastic, and diesel biodegradation activity were also carried out. Among the five non-streptomycetes isolates, only one newly found actinomycete isolate named as A9 exhibited significant biosurfactant and biodegradation activity. Based on Bergey's manual of systematic bacteriology, the strain A9 was similar to Nocardiopsis sp. Molecular characterization and phylogenetic analysis support the classification of the isolate as a new strain which was named as Nocardiopsis sp.mrinalini9. The isolate was closely related to the type strain of Nocardiopsis synnemataformans sharing a 16S rRNA gene sequence similarity of 99%. The partial 16S rRNA sequence of the isolate (1061 bp) was deposited in Genebank under the accession number KF909126. Still, DNA-DNA hybridizations, phenotypic comparisons, and chemotaxonomic analysis need to be performed to confirm its novelty. It is evident from the study that rare endphytes associated with medicinal plants has got excellent hydrocarbon biodegradation capacity.

Co-production of Pectinase and Biosurfactant by the Newly Isolated Strain Bacillus subtilis BKDS1

Aim: To isolate pectinase producing bacterial strains from various samples and to investigate the co-production of pectinase and biosurfactant by this isolated strain. Study Design: Isolation, screening, selection and identification of pectinolytic bacteria. Production of pectinase and analysis of exo-pectinase types. Partial purification by ammonium sulphate precipitation and dialysis. The study also analyses the capability of the selected strain for biosurfactant production. Place and Duration of Study: Department of Life Sciences, University of Calicut, Kerala 673635, India, between July 2013 and November 2014. Methodology: The pectinolytic bacteria was isolated and screened by iodine plate assay method. The enzyme production was confirmed by 3,5-dinitrosalicylic acid (DNS) method. The potent enzyme producing strain was biochemically characterised and identified by 16S rRNA gene sequence analysis. Thiobarbituric acid (TBA) and DNS assay were performed to test the types of exo-pectinase produced. Partial purification of the enzyme was done by ammonium sulphate precipitation. Biosurfactant production by the strain was tested by methods like foam formation, Original Research Article Kavuthodi et al.; BMRJ, 10(2): 1-12, 2015; Article no.BMRJ.19627 2 drop collapse test, oil displacement test, microplate assay, hemolytic assay, penetration assay, emulsification activity and bacterial adhesion to hydrocarbon (BATH) assay. Results: Thirty six pectinolytic bacterial strains were screened from the collected samples. Four isolates were selected on the basis of zone size (20 mm to 26 mm) in well plate screening method. In which, the isolate showed maximum enzyme production in DNS assay (0.707 U/mL) is the same which exhibited larger pectin depolymerization area (26 mm) in well diffusion assay. This strain was identified as Bacillus subtilis BKDS1 using 16S rDNA based molecular technique. The optimum incubation time was found to be 72 h for the maximum enzyme production (1.288 U/mL). Assay of exo-pectinase revealed that, the organism was able to produce polygalacturonase (PG), pectin lyase (PNL) and pectate lyase (PEL). In ammonium sulphate precipitation, the enzyme activity was found in 40 -100% salt saturation fractions. On further analysis, it was observed that the organism also produced biosurfactant along with pectinase in the same culture medium. Conclusion: The present study indicates the possibility of an integrated process for obtaining pectinase enzymes and biosurfactants in the same culture media. So this could greatly increase the economic viability of the isolated strain.

Degradation of oil and grease from high-strength industrial effluents using locally isolated aerobic biosurfactant-producing bacteria

The potential of oil and grease (O&G)-degrading ability of three local bacterial isolates was evaluated using wastewaters obtained from food processing, electrical and electronic and oil palm (POME) industries. These bacteria were chosen based on its high bacterial adherence to hydrocarbon (BATH), culture turbidity and maximum biosurfactant production (BSF) capabilities. From the 16S rRNA analysis, the food-processing isolate was identified and deposited in GenBank as Serratia marcescensEU555434, electrical & electronic (Aeromonas hydrophilaKF049214) and POME (Bacillus cereusKJ605415). Prior to evaluation for its O&G degradation ability (effect of contact time, different concentrations of wastewater, pH and initial organic loading rate), S. marcescens was adapted in used cooking oil while B. cereus in POME. S. marcescens, with the highest BSF and BATH values, showed maximum oil and grease degradation ability (91%) at pH 7.0 after 12 days of incubation and initial organic loading rate of 1.46 × 10−1 kgO&Gl−1day−1. For B. cereus, 100% (v/v) of POME (3012 mg l−1 oil and grease) was degraded after 7 days of incubation at 200 rpm, 30 °C and pH 6 while A. hydrophila was able to degrade 100% (v/v) of 4.88 mg l−1 of O&G from the electronic wastewater, supplemented with tryptone and lactose after only 2 h of incubation at 200 rpm, 30 °C at pH 7.0. The role of tryptone and lactose in complete biodegradation of O&G by A. hydrophila is significant as neither the addition of tryptone or lactose only resulted in enhanced O&G degradation, compared to E&E wastewater only. This finding showed the potential of using local aerobic bacterial isolates as an alternative solution to remove the presence of O&G in various industrial wastewaters.

Probiotic Attributes of Autochthonous Lactobacillus rhamnosus Strains of Human Origin

The study was aimed at evaluating the probiotic potential of indigenous autochthonous Lactobacillus rhamnosus strains isolated from infant feces and vaginal mucosa of healthy female. The survival of the selected strains and the two reference strains (L. rhamnosus GG and L. casei Actimel) was 67-81% at pH2 and 70-80% after passage through the simulated gastrointestinal fluid. These strains are able to grow in the presence of 4% bile salt, 10% NaCl, and 0.6% phenol. The cell surface of L. rhamnosus strains is hydrophilic in nature as revealed by bacterial adhesion to hydrocarbons (BATH) assay. Despite this, L. rhamnosus strains showed mucin adherence, autoaggregation and coaggregation properties that are strain-specific. In addition, they produce bile salt hydrolase (BSH) and β-galactosidase activities. L. rhamnosus strains exhibit antimicrobial activity against food spoilage organisms and gastrointestinal pathogens, as well as Candida and Aspergillus spp. L. rhamnosus strains have similar antibiotic susceptibility pattern, and resistance to certain antibiotics is intrinsic or innate. The strains are neither haemolytic nor producer of biogenic amines such as histamine, putrescine, cadaverine and tyramine. Lyophilized cells of L. rhamnosus Fb exhibited probiotic properties demonstrating potential of the strain for technological suitability and in the preparation of diverse probiotic food formulations.

Studying bacterial hydrophobicity and biofilm formation at liquid–liquid interfaces through interfacial rheology and pendant drop tensiometry

Bacterial adsorption to interfaces is a key factor in biofilm formation. One major limitation to understanding biofilm formation and development is the accurate measurement of bacterial cell adhesion to hydrophobic interfaces. With this study, bacterial attachment and biofilm growth over time at water–oil interface was monitored through interfacial rheology and tensiometry. Five model bacteria (Pseudomonas putida KT2442, Pseudomonas putida W2, Salmonella typhimurium, Escherichia coli, and Bacillus subtilis) were allowed to adsorb at the water–oil interface either in their non-growing or growing state. We found that we were able to observe the initial kinetics of bacterial attachment and the transient biofilm formation at the water–oil interface through interfacial rheology and tensiometry. Electrophoretic mobility measurements and bacterial adhesion to hydrocarbons (BATH) tests were performed to characterize the selected bacteria. To validate interfacial rheology and tensiometry measurements, we monitored biofilm formation utilizing both confocal laser scanning microscopy and light microscopy. Using this combination of techniques, we were able to observe the elasticity and tension development over time, from the first bacterial attachment up to biofilm formation.

Evaluation of Screening Methods for the Isolation of Biosurfactant Producing Marine Bacteria

Hemolytic assay, bacterial adhesion to hydrocarbons (BATH) assay, drop collapse assay, oil spreading assay, emulsification assay and surface tension measurement were compared for their reliability and ease of use to screen biosurfactant producing bacteria. 105 bacterial strains were screened for their biosurfactant production. Results from screening methods revealed that hemolytic and BATH assays are not reliable methods to check biosurfactant production because hemolytic assay relies on lysis of blood cells, which can be caused by compounds produced by microbes other than the biosurfactants. In that case hemolytic assay may include strains that do not produce biosurfactant. BATH assay relies on hydrophobicity or adherence of cells with hydrophobic compounds. Results obtained in BATH assay for three bacterial isolates, Branhamella catarrhalis, Citrobacter intermedius and Klebsiella ozaenae were positive, but when the same isolates screened for drop collapse, oil spreading, and surface tension measurement the results were negative. This indicates that these bacterial cells are either acting as biosurfactant themselves (cell surface) or they don’t have the ability to produce biosurfactants. In conclusion, drop collapse and oil spreading assays are reliable methods to screen large number of samples. However, for confirmation surface tension measurement can be used at the end. Another interesting finding in this study was the use of crude oil as hydrophobic substrate for the isolation of biosurfactant producing bacterial strains; this approach may be useful during the initial isolation of biosurfactant producing bacteria to reduce the number of strains to be screened.

Analysis of the Cell Surface Hydrophobicity of Yoghurt Fermentation Bacteria

The cell surface hydrophobicity (CSH) of lactic acid bacteria was considered to colonization and adhesion, and playing a prebiotic function in the digestive tract. Therefore, CSH of yoghurt fermentation bacteria most commonly used was analyzed, such as Lactobacillus acidophilus, Lactobacillus bulgaricus and Streptococcus thermophilus to identify initially CSH and the influencing factors of CSH of these strains and provided a theoretical basis for the future production of high-quality dairy fermentation agents and probiotics. The method of bacterial adhesion to hydrocarbons (BATH) was utilized to determine CSH of these strains and used the different conditions to process the cell. Through this research, the results was that L. acidophilus had a strong CSH, greater than L. bulgaricus and S. thermophilus. And the influencing factors of CSH of L. acidophilus were time, temperature, pH, concentration, Ca2+ and protease. But CSH was significantly reduced by trypsin and pepsin. CSH L. acidophilus was connected with the adhesion ability. In addition, it was speculated that some substances which could mediate CSH of L. acidophilus may be a class of proteins. Therefore, in the process of dairy fermentation agent, these factors could be controlled to obtain high-quality products.

CsgA Production by Escherichia coli O157:H7 Alters Attachment to Abiotic Surfaces in Some Growth Environments

The role of curli expression in attachment of Escherichia coli O157:H7 to glass, Teflon, and stainless steel (SS) was investigated through the creation of csgA knockout mutants in two isolates of E. coli O157:H7. Attachment assays using epifluorescence microscopy and measurements of the force of adhesion of bacterial cells to the substrates using atomic force microscopy (AFM) force mapping were used to determine differences in attachment between wild-type (wt) and csgA-negative (ΔcsgA) strains following growth in four different media. The hydrophobicity of the cells was determined using contact angle measurements (CAM) and bacterial adhesion to hydrocarbons (BATH). The attachment assay results indicated that ΔcsgA strains attached to glass, Teflon, and SS surfaces in significantly different numbers than their wt counterparts in a growth medium-dependent fashion (P < 0.05). However, no clear correlation was seen between attachment numbers, surface type, or growth medium. No correlation was seen between BATH and CAM results (R(2) < 0.70). Hydrophobicity differed between the wt and ΔcsgA in some cases in a growth medium- and method-dependent fashion (P < 0.05). AFM force mapping revealed no significant difference in the forces of adhesion to glass and SS surfaces between wt and ΔcsgA strains (P > 0.05) but a significantly greater force of adhesion to Teflon for one of the two wt strains than for its ΔcsgA counterpart (P < 0.05). This study shows that CsgA production by E. coli O157:H7 may alter attachment behavior in some environments; however, further investigation is required in order to determine the exact relationship between CsgA production and attachment to abiotic surfaces.

High-density polyethylene (HDPE)-degrading potential bacteria from marine ecosystem of Gulf of Mannar, India

Assessment of high-density polyethylene (HDPE)-degrading bacteria isolated from plastic waste dumpsites of Gulf of Mannar. Rationally, 15 bacteria (GMB1-GMB15) were isolated by enrichment technique. GMB5 and GMB7 were selected for further studies based on their efficiency to degrade the HDPE and identified as Arthrobacter sp. and Pseudomonas sp., respectively. Assessed weight loss of HDPE after 30 days of incubation was nearly 12% for Arthrobacter sp. and 15% for Pseudomonas sp. The bacterial adhesion to hydrocarbon (BATH) assay showed that the cell surface hydrophobicity of Pseudomonas sp. was higher than Arthrobacter sp. Both fluorescein diacetate hydrolysis and protein content of the biofilm were used to test the viability and protein density of the biomass. Acute peak elevation was observed between 2 and 5 days of inoculation for both bacteria. Fourier transform infrared (FT-IR) spectrum showed that keto carbonyl bond index (KCBI), Ester carbonyl bond index (ECBI) and Vinyl bond index (VBI) were increased indicating changes in functional group(s) and/or side chain modification confirming the biodegradation. The results pose us to suggest that both Pseudomonas sp. and Arthrobacter sp. were proven efficient to degrade HDPE, albeit the former was more efficacious, yet the ability of latter cannot be neglected. Recent alarm on ecological threats to marine system is dumping plastic waste in the marine ecosystem and coastal arena by anthropogenic activity. In maintenance phase of the plastic-derived polyethylene waste, the microbial degradation plays a major role; the information accomplished in this work will be the initiating point for the degradation of polyethylene by indigenous bacterial population in the marine ecosystem and provides a novel eco-friendly solution in eco-management.

Carbon content reduction in a model reluctant clayey soil: Slurry phase n-hexadecane bioremediation

Clayey soils contaminated with organic pollutants are nowadays one of the important environmental issues as they are highly reluctant to conventional bioremediation techniques. In this study, biodegradability of n-hexadecane as a model contaminant in oil polluted clayey soil by an indigenous bacterium was investigated. Maximal bacterial growth was achieved at 8% (v/v) n-hexadecane as sole carbon and energy sources in aqueous phase. The predominant n-hexadecane uptake mechanism was identified to be biosurfactant-mediated using bacterial adhesion to hydrocarbon (BATH) test and surface tension measurements. The effect of n-hexadecane concentration, soil to water ratio, inoculum concentration and pH on total organic carbon (TOC) reduction from kaolin soil in slurry phase was investigated at two levels in shake flasks using full factorial experimental design method where 10,000 (mg n-hexadecane)(kg soil) −1, soil–water ratio of 1:3, 10% (v/w) inoculum and pH of 7 resulted in the highest TOC reduction of 70% within 20 days. Additionally, slurry bioreactor experiments were performed to study the effect of various aeration rates on n-hexadecane biodegradation during 9 days where 2.5 vvm was found as an appropriate aeration rate leading to 54% TOC reduction. Slurry phase bioremediation is shown to be a successful method for remediation of clayey reluctant soils.

Measuring ‘hydrophobicity’ of filamentous bacteria found in wastewater treatment plants

Attempts to measure the hydrophobicity of the cell surfaces of Gordonia amarae and Rhodococcus erythropolis, filamentous bacteria found in wastewater treatment plants, by several methods—microbial adhesion to hydrocarbons (MATH) or bacterial adhesion to hydrocarbons (BATH), contact angle, and micro-sphere adhesion to cells (MAC)—were unsuccessful. The results were erratic and inconsistent. This was in part because of the filamentous growth habit of G. amarae, but it was also a consequence of the fact that the ‘hydrophobicity’ of bacterial cells is not a clearly defined quantity. A technique is introduced in which bacteria are suspended in solutions of synthetic surfactants (non-ionic, cationic and anionic), and the suspensions aerated under defined conditions. The partitioning of bacterial cells between the foam and liquid phases was reproducible. The method was tested in model systems in which the bacteria were replaced by silica particles with defined surface modifications. Although this technique is not a direct measure of ‘hydrophobicity’, the partitioning of cells depends in part upon their surface hydrophobicity. In addition, qualitative information is gained about ionic interactions between the bacteria and the bubble surface. The results are pertinent to the problem of foaming in wastewater treatment plants.

Salmonella Sofia Differs from Other Poultry-Associated Salmonella Serovars with Respect to Cell Surface Hydrophobicity

Salmonella enterica is one of the most important foodborne pathogens. Salmonella enterica subsp. II 4,12:b:– (Salmonella Sofia) is commonly found in Australian poultry. It has been suggested that physicochemical properties such as surface charge and hydrophobicity may affect bacterial attachment to surfaces and their ability to persist in food systems. A possible link between hydrophobicity cell surface charge and persistence of Salmonella from the poultry system was examined. Hydrophobicity of Salmonella Sofia (n = 14), Salmonella Typhimurium (n = 6), Salmonella Infantis (n = 3), and Salmonella Virchow (n = 2) was assayed using hydrophobic interaction chromatography, bacterial adherence to hydrocarbons (BATH), using xylene or hexadecane, and the contact angle method (CAM). Cellular surface charge (CSC) of the isolates was determined using zeta potential measurements. The majority (12 of 14) of Salmonella Sofia isolates were found to be hydrophobic when assayed using BATH with xylene, except isolates S1635 and S1636, and the other serovars were found to be hydrophilic. Salmonella Sofia isolates were not significantly different (P > 0.05) from isolates of other serovars as measured by hydrophobic interaction, BATH with hexadecane, or the CAM. No significant differences (P > 0.05) in zeta potential measurements were observed between isolates. Principal component analysis using results from all four measures of hydrophobicity allowed clear differentiation between isolates of the serovar Salmonella Sofia (except S1635 and S1636) and those of other Salmonella serovars. Differences in physicochemical properties may be a contributing factor to the Salmonella Sofia serovar's ability to attach to surfaces and persist in a food system.

A Comparison of Various Methods to Predict Bacterial Predilection for Organic Solvents Used as Reaction Media

Bacterial predilection for organic solvents is important in whole-cell biocatalysis in organic media. Although various methods of measuring bacterial hydrophobicity have been proposed, it is not fully determined whether they are applicable to the assessment of bacterial predilection for organic solvents in whole-cell biocatalytic processes. In this study, bacterial predilection for organic solvents was assessed by bacterial adhesion to hydrocarbon (BATH), contact angle measurement (CAM), hydrophobic interaction chromatography (HIC), and glass adhesion test (GAT). These methods were applied to the cultures of four bacterial species of industrial importance, namely, Rhodococcus opacus B-4, R. erythropolis PR4, Pseudomonas putida T-57, and Escherichia coli JM109, in organic media. Experimental results revealed that CAM assays could be used to predict the dispersibility of bacterial cells in anhydrous organic solvents. However, when bacteria were suspended in aqueous-organic (A/O) two-phase media, the results of BATH assays provided the most reliable assessment of bacterial predilection for organic solvents. This discrepancy noted between CAM and BATH assays was attributed to the effect of electrostatic interaction between bacteria and oil droplets. In A/O two-phase media, the accessibility of a water-immiscible dye, nile red, to the bacterial cell surface, correlated well with BATH assay results.

Experimental and QSAR of Acetophenones as Antibacterial Agents

Antibacterial activity of 20 acetophenone derivatives was evaluated against two Gram-positive and three Gram-negative organisms, namely, Bacillus subtilis NCIM 2718, Staphylococcus aureus NCIM5021, Salmonella typhi NCIM2501, Enterobacter aerogenes NCIM5139, and Proteus vulgaris NCIM2813 by two-fold dilution method. The most active amongst this group of compounds were 4-methyl, 2-hydroxy, 3-bromo, 4-ethoxy, 3-nitro and 4-nitro acetophenones. Quantitative structure-activity relationships were developed by dividing the data into training and validation sets, the former was used to develop and the latter was used to test the models. Spatial, electronic and topological descriptors were predominantly found to influence the activity. The statistical measures such as r( 2) (0.76-0.91), cross-validated r( 2) (0.56-0.85), F-ratio and predicted residual sum of square values were found to be in the acceptable range. The developed models were able to predict the activity of the validation data set within the 99% confidence limit (except for two data points). 4-Nitroacetophenone was found to be the most slimicidal in nature. Bacterial Adhesion to Hydrocarbons (BATH) assay indicated that Staphylococcus aureus NCIM5021 had the most hydrophobic cell surface of these five organisms. Cell surface hydrophobicity of organisms also had an impact on the antibacterial activity of the acetophenones.

Evaluation of Adherence, Hydrophobicity, Aggregation, and Biofilm Development of Flavobacterium johnsoniae-Like Isolates

Flavobacterium spp. isolates have been identified in diverse biofilm structures, but the mechanism of adherence has not been elucidated. The absence of conventional biofilm-associated structures such as fimbriae, pili, and flagella suggest that surface hydrophobicity, and/or autoaggregation and coaggregation may play an important role in adherence and biofilm formation. The biofilm-forming capacity of 29 Flavobacterium johnsoniae-like isolates obtained from South African aquaculture systems was assessed using microtiter plate assays. The role of hydrophobicity [salting aggregation test (SAT) and bacterial adherence to hydrocarbons (BATH) assays], autoaggregation, and coaggregation on biofilm formation by Flavobacterium spp. was also investigated, while biofilm structure was examined using flow cells and microscopy. All isolates displayed a hydrophilic nature, but showed varying levels of adherence in microtiter assays. Significant negative correlations were observed between adherence and biofilm-forming capacity in nutrient-poor medium at 26 degrees C and BATH hydrophobicity and motility, respectively. Isolates displayed strain-to-strain variation in their autoaggregation indices and their abilities to coaggregate with various Gram-negative and Gram-positive organisms. Microcolony and/or biofilm development were observed microscopically, and flavobacterial isolates displayed stronger biofilm structures and interaction with a Vibrio spp. isolate than with an Aeromonas hydrophila isolate. The role of extracellular polysaccharides and specific outer membrane proteins will have to be examined to reveal mechanisms of adherence and coaggregation employed by biofilm-forming F. johnsoniae-like strains.

Growth and physiological response of Arthrobacter protophormiae RKJ100 toward higher concentrations of o-nitrobenzoate and p-hydroxybenzoate

Bioremediation of sites that are heavily contaminated with pollutant chemicals is a challenge as most of the microorganisms cannot tolerate higher concentrations of toxic compounds. Only a few strains of the genus Pseudomonas have been studied for their tolerance toward the higher concentrations of aromatic pollutant compounds, a phenomenon that is accompanied by various physiological changes. In the present study we have characterized the growth response and physiological changes (adaptations) of a Gram-positive bacterium, Arthrobacter protophormiae RKJ100, toward the higher concentrations of two aromatic compounds, viz. o-nitrobenzoate (ONB) and p-hydroxybenzoate (PHB). Arthrobacter protophormiae RKJ100 could utilize 30 mM ONB and 50 mM PHB as sole sources of carbon and energy. It was capable of growth on higher concentrations of ONB (up to 200 mM) and PHB (up to 150 mM) when the cells were pre-exposed to lower concentrations of these compounds. The adaptive responses shown by the organism during growth on higher concentrations of these compounds were evident from significant changes in cellular fatty acid profiles. In addition, Bacterial Adhesion To Hydrocarbon (BATH) assay and scanning electron microscopy showed substantial increase in cell surface hydrophobicity and decrease in cell size of A. protophormiae RKJ100 when grown on ONB and PHB as compared to succinate-grown cells.

Insight into heterogeneity in cell-surface hydrophobicity and ability to degrade hydrocarbons among cells of two hydrocarbon-degrading bacterial populations

The sequential bacterial adherence to hydrocarbons (BATH) of successive generations of hydrophobic fractions of Paenibacillus sp. R0032A and Burkholderia cepacia gave rise to bacterial populations of increasing cell-surface hydrophobicity. Thus, hydrophobicity of the first generation (H1) was less than that of the second generation (H2), which was less than that of the third generation (H3). Beyond H3, the hydrophobic populations became less stable and tended to lyse in hexadecane after violent (vortex) agitation, resulting in an apparent decline in BATH value. The exhaustively fractionated aqueous-phase population (L) was very hydrophilic. The overall cell-surface distribution of the population was L < parental strain < H1 < H2 < H3. The ability to degrade crude oil, hexadecane, or phenanthrene matched the degree of cell-surface hydrophobicity: L < P < H1 < H2 < H3. Thus, in natural populations of hydrocarbon-degrading Paenibacillus sp. R0032A and B. cepacia, there is a heterogeneity in the hydrophobic surface characteriistics that affects the ability of cells to use various hydrocarbon substrates.

Effects of physicochemical surface characteristics of Listeria monocytogenes strains on attachment to glass

Seven strains of Listeria monocytogenes frequently involved in foodborne disease (epidemic strains) and 14 sporadic strains were examined to compare the attachment and subsequent biofilm growth on glass slides at 37 °C. Epidemic strains at 3 h incubation had significantly higher attachment values than sporadic strains ( P < 0.001 ), but subsequent biofilm growth over 24 h was not dependent on initial attachment. To better understand this phenomenon, the surface hydrophobicity and charge, as well as the extracellular carbohydrate content of the 21 L. monocytogenes strains were studied to determine if these surface characteristics had an effect on bacterial attachment to glass. Hydrophobicity was measured by the bacterial adherence to hydrocarbon (BATH) and polystyrene adherence methods. Hydrophobicity values obtained with the BATH method were linearly correlated with those from the polystyrene adherence method ( r = 0.64 , P < 0.001 ), but no correlation was found between hydrophobicity and bacterial attachment to glass. Hydrophobicity and surface charge measured as electrophoretic mobility (EM) were correlated ( r = 0.77 , P < 0.001 ); however, there was no correlation between the degree of attachment and surface charge. Colorimetric measurements of the total extracellular carbohydrates revealed that attached cells produced significantly ( P < 0.05 ) higher levels than planktonic cells after a 3 h time period. Analysis of co-variance (Nested ANCOVA) furthermore demonstrated that total carbohydrates produced by planktonic cells had a significant positive effect on 24 h biofilm growth ( P = 0.006 ). This is the first report to indicate that the ability of a L. monocytogenes strain to produce high levels of extracellular carbohydrates may increase its ability to form a biofilm. Genetic studies targeting carbohydrate synthesis pathways of L. monocytogenes will be required to fully understand the importance of this observation.

Hydrophobicity and surface electrostatic charge of conidia of the mycoparasitic Trichoderma species

The present investigation was done to understand the fungal-fungal interactions mechanisms based on level of nonspecific adhesion of a potential fungal mycoparasite (Trichoderma) to their fungal host (Macrophomina phaseolina). The relative cell surface hydrophobicity (CSH) and cell surface electrostatic charge (CSEC) of 29 isolates of Trichoderma species, analyzed by bacterial adhesion to hydrocarbon (BATH), hydrophobic interaction chromatography (HIC), microelectrophoresis and contact angle, revealed a large degree of variability. CSH and CSEC of conidia depended on culture age, pH and temperature. Maximum CSH and CSEC were recorded in 25–28 °C range, and both declined significantly with increasing temperature. Isolate Trichoderma hazianum (Th)-23/98 expressed surface hydrophobicity at 25–28 °C and hydrophilicity at 40 °C. Surface hydrophobicity of the isolate was susceptible to various proteases (trypsin, pepsin, proteinase k and a-chymotrypsin) and inhibitors (SDS, mercaptoethanol and Triton X-100) and a significant reduction in CSH was recorded in hydrophobic conidia. Hydrophilic conidia remained more or less unaffected by such treatments. SDS-PAGE analysis of the hydrophobic and hydrophilic conidia exhibited several protein bands in the 25 to 61 kDa range. However, each protein population contained one protein that was not observed in the other population. For hydrophobic conidia, the unique protein had an apparent molecular mass of 49 kDa, while the unique protein associated with hydrophilic conidia had a molecular mass of 61 kDa. Our findings suggest that CSH and CSEC of mycoparasitic Trichoderma may contribute to non-specific adhesion on to the sclerotial surfaces of Macrophomina phaseolina that may be influenced by growth and environmental conditions.

The effect of NAG–thiazoline on morphology and surface hydrophobicity ofEscherichia coli

The β-hexosaminidase inhibitor and structural analog of the putative oxazolium reaction intermediate of lytic transglycosylases, N-acetylglucosamine thiazoline (NAG–thiazoline), was synthesized in 46% overall yield and tested as an inhibitor of Escherichia coli growth. NAG–thiazoline, at concentrations up to 1 mg/ml, was not found to affect the viability of E. coli DH5α. However, the compound did induce morphological changes to the cells. Growth of cells in the presence of NAG–thiazoline caused an apparent inhibition of the biosynthesis of the cylindrical regions of the cells such that they became much shorter in length. The surface of these shorter cells was found to be much less hydrophobic compared to untreated cells as determined by the bacterial adhesion to hydrocarbon (BATH) assay. In addition, the co-administration of NAG–thiazoline with 1.7 × MIC concentrations of ampicillin prevented cell lysis suggesting that the compound inhibited autolytic enzymes, in particular the lytic transglycosylases.