Low-cost fermentative medium for biosurfactant production by Streptococcus thermophilus A

Interest in biosurfactants has increased considerably in recent years, as they are potential candidates for many commercial applications in the petroleum, pharmaceuticals, biomedical and food processing industries. Biosurfactants have several advantages over chemical s urfactants including lower toxicity and higher biodegradability, and effectiveness at extreme temperatures or pH values. In spite of the advantages, fermentation must be cost competitive with chemical synthesis and many of the potential applications that have been considered for biosurfactants depend on whether they can be produced economically. The use of alternative molasses medium (sucrose content 20 g/L, supplemented with 3 g/L yeast extract and 5 g/L peptone) for biosurfactant production by Streptococcus thermophilus A was studied. Suitable models were established to describe the response of the experiments pertaining to glucose or sucrose consumption, cell growth and biosurfactant production. Conventional synthetic M17 broth was used as control experiments. The replacement of M17 broth by cheaper molasses medium resulted on an increase about 1.4 times in the mass of produced biosurfactant (mg) per gram cell dry weight and a 80% medium preparation costs reduction.In con clusion, the results obtained showed that molasses medium can be used as a relatively inexpensive and economical alternative to conventional synthetic medium for biosurfactant production by S. thermophilus A

Low-cost fermentative medium for biosurfactant production by probiotic bacteria

Potential use of alternative fermentative medium for biosurfactant production by Lactococcus lactis 53 and Streptococcus thermophilus A was studied. Suitable models were established to describe the response of the experiments pertaining to glucose, lactose or sucrose consumption, cell growth and biosurfactant production. Synthetic media MRS and M17 broth were used as control experiments. When the synthetic media were replaced by cheaper alternative media, as cheese whey and molasses, fermentations were carried out effectively with high yields and productivities of biosurfactant. An increase about 1.2–1.5 times in the mass of produced biosurfactant per gram cell dry weight and 60–80% medium preparation costs reduction were achieved, for both strains. In conclusion, the results obtained showed that supplemented cheese whey and molasses media can be used as a relatively inexpensive and economical alternative to synthetic media for biosurfactant production by probiotic bacteria, thus an attractive alternative as many of the potential applications for biosurfactants depend on whether they can be produced economically.Fundação para a Ciência e a Tecnologia (FCT

Polysaccharide production and biofilm formation by Pseudomonas fluorescens: effects of pH and surface material

Although the synthesis of extracellular polysaccharides was first recognized in certain bacterial cultures a long time ago, its role in bacterial adhesion is still subject to some debate. Several fermentation batch cultures were performed under different conditions of pH (pH 7, maintained with NaOH and HCl; pH 7 in phosphate buffer, and without pH control) in order to study the relation between the production of extracellular polysaccharides and biofilm formation on polymeric slides suspended in the culture medium. The polymers used were polystyrene, polypropylene, polyethylene and poly(vinyl chloride). The maximum amount of exopolysaccharides in the culture medium occurs at pH 7, although slightly thicker biofilms seem to be formed when there is no pH control. The biofilms were analysed by scanning electron microscopy and by wavelength dispersion spectroscopy. Biofilm morphology seems to be much more dependent on the type of substratium than on the pH of the medium; for different pH values, a polymeric network can be more clearly observed on biofilms formed on all surfaces except poly(vinyl chloride)

Impact of biofilms in simulated drinking water and urban heat supply systems

Biofouling and biocorrosion were studied in drinking water and heating water systems by forming biofilms on steel and on polymethylmetacrylate. In the drinking water system, biofilm development was more significant on corroded surfaces, suggesting that in these conditions they were largely protected from disinfection, probably because of sheltering and chlorine demand by corrosion products. In the urban heat supply system, results suggest a higher biofilm activity at lower pH. Sulphate-reducing bacteria were detected in the urban heating biofilms, but little corrosion was observed on steel coupons. Results indicate that surface and bulk medium properties, as well as bacterial diversity are determinant parameters when studying biofouling and biocorrosion.Cirius – Danish Centre for International Cooperation and Mobility in Education and Trainin

Kinetic study of fermentative biosurfactant production by Lactobacillus strains

Screening of biosurfactant-producing ability of four Lactobacillus strains was performed, being shown that for all the tested strains biosurfactant production occurred mainly in the first 4 h. The Lactobacillus strains showed zones of clearing in the blood agar with a diameter <1 cm. The minimum surface tension value of the fermentation broth achieved was 39.5 mN/m for Lactobacillus pentosus CECT-4023 that represents a reduction in the surface tension of 10.5 mN/m comparing with the control. Time courses of glucose, biomass and biosurfactant were modeled according to reported models. Using MRS broth (Man, Rogosa & Sharpe medium for lactobacilli strains) as culture medium, the values estimated by the modeling of biosurfactant were Pmax = 1.6 g of biosurfactant/L and rp/X = 0.091 g/(L h), for Lactobacillus casei CECT-5275, Pmax = 1.7 g/L and rp/X = 0.217 g/(L h) for Lactobacillus rhamnosus CECT-288, Pmax = 1.7 g/L and rp/X = 0.069 g/(L h) for L. pentosus CECT-4023 and Pmax = 1.8 g/L and rp/X = 0.090 g/(L h) for Lactobacillus coryniformis subsp. torquens CECT-25600. Pmax is the maximum concentration of biosurfactant (g/L), and Pr is the ratio between the initial volumetric rate of product formation (rp) and the initial product concentration P0 (g/L). Using whey as production medium, the values estimated by the modeling of biosurfactant for L. pentosus CECT-4023 were Pmax = 1.4 g of biosurfactant/L and rp/X = 0.093 g/(L h). In conclusion, the results obtained for L. pentosus CECT-4023 showed that this is a strong biosurfactant producer strain and that cheese whey can be used as an alternative medium for biosurfactant production

The effect of dissolved stainless steel alloy elements on the activity and growth of SRB

Sulphate reducing bacteria have an important role in the sulphur cycle, and therefore in wastewater treatment systems. They are able to form biofilms on metallic surfaces, leading to fouling and corrosion problems. These bacteria are among the micro-organisms most frequently implicated in microbial corrosion of iron and ferrous alloys. Alloying elements added to steels for the improvement of their corrosion resistance such as molybdenum and nickel can be dissolved in bulk liquid during the corrosion processes and therefore available to the micro-organisms. That may affect bacterial metabolism and adhesion. In this study, suspended cultures of sulphate reducing bacteria (SRB) were subjected to several nickel concentrations in order to evaluate the effect of the dissolved metal on bacterial metabolism. Simultaneously, SRB biofilms were developed on stainless steel 304 and on polymethylmethacrylate (PMMA) in order to study surface effect on biofilm formation. Results showed that nickel (Ni) in all tested concentrations between 0.006 and 5 mg/L had a positive effect on the growth of Desuljovibrio desulfuricans. Additionally, biofilms formed on stainless steel presented higher metabolic activity, confirmed by sulphate removal and acetate concentration in the effluent stream. Metal elements present in stainless steel may affect SRB activity. This can be the case of nickel that represents around 8% of stainless steel 304 and that had a positive impact on suspended SRB cultures, under the tested concentrations

Modeling of biosurfactant production by Lactobacillus Strains

Screening of biosurfactant-producing ability of three Lactobacillus strains was performed, being shown that, for all the tested strains, biosurfactant production is occurring mainly in the first 7 hours. All strains reduced 8 mN/m the surface tension of the fermentation broth at the end of fermentation and lysed blood agar with scores ranging between (++) corresponding to complete hemolysis with a diameter < 1 cm. Time courses of lactose, biomass and biosurfactant were modeled according to reported models, assuming product inhibition. Using optimized MRS broth as culture medium, the values estimated by the modeling of biosurfactant were P_max = 1.4 g of biosurfactant/L and rp/X = 0.137g/L.hˉ¹ for Lactobacillus casei CECT-5275, P_max = 1.5 g/L and rp/X = 0.145g/L.hˉ¹ for Lactobacillus rhamnosus CECT-288 and P_max = 1.5 g/L and rp/X = 0.089 g/L.hˉ¹ for Lactobacillus pentosus CECT-4023. Using whey as production medium, the values obtained for Lactobacillus rhamnosus CECT-288 were P_max = 1.3 g of biosurfactant/L and rp/X = 0.078 g/L.hˉ¹. In conclusion, the results obtained showed that whey can be used as an alternative medium for biosurfactant production by Lactobacillus strains

The influence of surface material on the development of Desulfovibrio desulfuricans biofilms

Sulphate reducing bacteria have an important role in the sulphur cycle, and therefore in wastewater treatment systems. They are able to form biofilms on metallic surfaces, leading to fouling and corrosion problems. Additionally, hydrogen sulphide that is a product of their metabolism can cause serious health risks. In this study, sulphate reducing bacteria (SRB) biofilms were developed on stainless steel 304 and on polycarbonate in order to evaluate surface effect on biofilm formation. Results showed that the biofilm formed on stainless steel presented higher metabolic activity, confirmed by lactate and sulfate removals. Metal elements present in stainless steel may affect SRB activity. This can be the case of nickel that represents around 8% of stainless steel 304. Studies performed with suspended cultures of Desulfovibrio desulfuricans also showed that the presence of nickel in the media had a positive impact on bacterial activity

The influence of nickel on the adhesion ability of Desulfovibrio desulfuricans

The build-up of biofilms on metals surfaces may lead to severe corrosion, especially in the presence of sulphate-reducing bacteria (SRB). To prevent the deterioration of material caused by biofilms it is necessary to understand the processes governing biofilm development including mechanisms of cell adhesion. Additionally, corrosion of metallic surfaces due to bacteria may lead to the dissolution of metallic elements that may further affect adhesion and biofilm development. A study was carried out to evaluate how the presence of nickel in the substrata affects the adhesion ability of Desulfovibrio desulfuricans. The substrata tested were stainless steel 304 (SS), metallic nickel (Ni) and polymethylmetacrylate (PMMA), a non-metallic material used as control. The influence of nickel on SRB growth and its relation to adhesion was also checked. A statistically significant difference in the number of adhered cells to the materials tested was detected, with higher bacterial number on nickel, followed by SS and finally by PMMA. The higher number of SRB adhered to steel compared with PMMA may be explained by differences in hydrophobicity, in roughness and in the electron-acceptor character of the substrata. Additionally, bacterial growth was found to be positively affected by the presence of nickel as revealed by a significant increase in the specific growth rate of SRB in the presence of increased nickel concentrations.Programme Praxis XXI