Surfactants in microbiology and biotechnology: Part 2. Application aspects

Using enzymes to remove biofilms of bacterial isolates sampled in the food-industry

The aim of this study was to analyze the cleaning efficiency of polysaccharidases and proteolytic enzymes against biofilms of bacterial species found in food industry processing lines and to study enzyme effects on the composition of extracellular polymeric substances (EPS) and biofilm removal in a Clean-in-Place (CIP) procedure. The screening of 7 proteases and polysaccharidases for removal of biofilms of 16 bacterial species was first evaluated using a microtiter plate assay. The alkaline pH buffer removed more biofilm biomass as well as affecting a larger range of bacterial species. The two serine proteases and alpha-amylase were the most efficient enzymes. Proteolytic enzymes promoted biofilm removal of a larger range of bacterial species than polysaccharidases. Using three isolates derived from two bacterial species widely found in food processing lines (Pseudomonas fluorescens and the Bacillus cereus group), biofilms were developed on stainless steel slides and enzymatic solutions were used to remove the biofilms using CIP procedure. Serine proteases were more efficient in removing cells of Bacillus biofilms than polysaccharidases. However, polysaccharidases were more efficient in removing P. fluorescens biofilms than serine proteases. Solubilization of enzymes with a buffer containing surfactants, and dispersing and chelating agents enhanced the efficiency of polysaccharidases and proteases respectively in removing biofilms of Bacillus and P. fluorescens. A combination of enzymes targeting several components of EPS, surfactants, dispersing and chelating agents would be an efficient alternative to chemical cleaning agents.

Microbial biosurfactants production, applications and future potential

Microorganisms synthesise a wide range of surface-active compounds (SAC), generally called biosurfactants. These compounds are mainly classified according to their molecular weight, physico-chemical properties and mode of action. The low-molecular-weight SACs or biosurfactants reduce the surface tension at the air/water interfaces and the interfacial tension at oil/water interfaces, whereas the high-molecular-weight SACs, also called bioemulsifiers, are more effective in stabilising oil-in-water emulsions. Biosurfactants are attracting much interest due to their potential advantages over their synthetic counterparts in many fields spanning environmental, food, biomedical, and other industrial applications. Their large-scale application and production, however, are currently limited by the high cost of production and by limited understanding of their interactions with cells and with the abiotic environment. In this paper, we review the current knowledge and the latest advances in biosurfactant applications and the biotechnological strategies being developed for improving production processes and future potential.

Bioemulsifier production byMicrobacterium SP. strains isolated from mangrove and their application to remove cadmiun and zinc from hazardous industrial residue

The contamination of ecosystems with heavy metals is an important issue in current world and remediation technologies should be in according to environmental sustainability concept. Bioemulsifier are promising agents to be used in metal removal and could be effective to many applications in environmental industries. The aims of this work was screening the potential production of bioemulsifier by microorganisms isolated from an oil contaminated mangrove, and evaluate cadmium and zinc removal potential of those strains from a hazardous industrial residue. From that, bioemulsifier-producing bacteria were isolated from urban mangrove sediments. Four isolates were identified as Microbacterium sp by 16S rRNA analysis and were able to reduce up to 53.3% of culture medium surface tension (TS) when using glucose as carbon and energy source and 20.2% when sucrose was used. Suspensions containing bioemulsifier produced by Microbacterium sp. strains show to be able to remove cadmium and zinc from contaminated industrial residue, and its ability varied according carbon source. Significant differences in metal removal were observed by all strains depending on the carbon source. When glucose was used, Cd and Zn removal varied from 17 to 41%, and 14 to 68%, respectively. However, when sucrose was used it was observed only 4 to a maximum of 15% of Cd removal, and 4 to 17% of Zn removal. When the same tests were performed after ethanol precipitation, the results were different: the percentages of removal of Zn (7–27%) and Cd (14–32%) were higher from sucrose cultures. This is the first report of heavy metals removal by bioemulsifier from Microbacterium sp.

Antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20

AIMS

The aim of this study was to determine the antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20 against several micro-organisms, including Gram-positive and Gram-negative bacteria, yeasts and filamentous fungi.

METHODS AND RESULTS

Antimicrobial and antiadhesive activities were determined using the microdilution method in 96-well culture plates. The biosurfactant showed antimicrobial activity against all the micro-organisms assayed, and for twelve of the eighteen micro-organisms (including the pathogenic Candida albicans, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus agalactiae), the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were achieved for biosurfactant concentrations between 25 and 50 mg ml(-1). Furthermore, the biosurfactant showed antiadhesive activity against most of the micro-organisms evaluated.

CONCLUSIONS

As far as we know, this is the first compilation of data on antimicrobial and antiadhesive activities of biosurfactants obtained from lactobacilli against such a broad group of micro-organisms. Although the antiadhesive activity of biosurfactants isolated from lactic acid bacteria has been widely reported, their antimicrobial activity is quite unusual and has been described only in a few strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained in this study regarding the antimicrobial and antiadhesive properties of this biosurfactant opens future prospects for its use against micro-organisms responsible for diseases and infections in the urinary, vaginal and gastrointestinal tracts, as well as in the skin, making it a suitable alternative to conventional antibiotics.

Possibilities and challenges for biosurfactants use in petroleum industry

Biosurfactants are a group of microbial molecules identified by their unique capabilities to interact with hydrocarbons. Emulsification and de-emulsification, dispersion, foaming, wetting and coating are some of the numerous surface activities that biosurfactants can achieve when applied within systems such as immiscible liquid/liquid (e.g., oil/water), solid/ liquid (e.g., rock/oil and rock/water) and gas/liquid. Therefore, the possibilities of exploiting these bioproducts in oil-related sciences are vast and made petroleum industry their largest possible market at present. The role of biosurfactants in enhancing oil recovery from reservoirs is certainly the best known; however they can be effectively applied in many other fields from transportation of crude oil in pipeline to the clean-up of oil storage tanks and even manufacturing of fine petrochemicals. When properly used, biosurfactants are comparable to traditional chemical analogues in terms of performances and offer advantages with regard to environment protection/conservation. This chapter aims at providing an up-to-date overview of biosurfactant roles, applications and possible future uses related to petroleum industry.

Microbial biosurfactants and biodegradation

Microbial biosurfactants are amphipathic molecules having typical molecular weights of 500-1500 Da, made up of peptides, saccharides or lipids or their combinations. In biodegradation processes they mediate solubilisation, mobilization and/or accession of hydrophobic substrates to microbes. They may be located on the cell surface or be secreted into the extracellular medium and they facilitate uptake of hydrophobic molecules through direct cellular contact with hydrophobic solids or droplets or through micellarisation. They are also involved in cell physiological processes such as biofilm formation and detachment, and in diverse biofilm associated processes such as wastewater treatment and microbial pathogenesis. The protection of contaminants in biosurfactants micelles may also inhibit uptake of contaminants by microbes. In bioremediation processes biosurfactants may facilitate release of contaminants from soil, but soils also tend to bind surfactants strongly which makes their role in contaminant desorption more complex. A greater understanding of the underlying roles played by biosurfactants in microbial physiology and in biodegradative processes is developing through advances in cell and molecular biology.

Biomedical and therapeutic applications of biosurfactants

During the last years, several applications of biosurfactants with medical purposes have been reported. Biosurfactants are considered relevant molecules for applications in combating many diseases and as therapeutic agents due to their antibacterial, antifungal and antiviral activities. Furthermore, their role as anti-adhesive agents against several pathogens illustrate their utility as suitable anti-adhesive coating agents for medical insertional materials leading to a reduction of a large number of hospital infections without the use of synthetic drugs and chemicals. Biomedical and therapeutic perspectives of biosurfactants applications are presented and discussed in this chapter.

Isolation and functional characterization of a biosurfactant produced by Lactobacillus paracasei

In this study, the crude biosurfactant produced by a Lactobacillus paracasei strain isolated in a Portuguese dairy industry was characterized. The minimum surface tension (41.8mN/m) and the critical micelle concentration (2.5mg/ml) obtained were found to be similar to the values previously reported for biosurfactants isolated from other lactobacilli. The biosurfactant was found to be stable to pH changes over a range from 6 to 10, being more effective at pH 7, and showed no loss of surface activity after incubation at 60 degrees C for 120h. Although the biosurfactant chemical composition has not been determined yet, a fraction was isolated through acidic precipitation, which exhibited higher surface activity as compared with the crude biosurfactant. Furthermore, this isolated biosurfactant showed antimicrobial and anti-adhesive activities against several pathogenic microorganisms. In addition, L. paracasei exhibited a strong autoaggregating phenotype, which was maintained after washing and resuspending the cells in PBS, meaning that this attribute must be related to cell surface components and not to excreted factors. The autoaggregation ability exhibited by this strain, together with the antimicrobial and anti-adhesive properties observed for this biosurfactant opens the possibility for its use as an effective probiotic strain.

Aqueous phase partitioning of hexachlorocyclohexane (HCH) isomers by biosurfactant produced by Pseudomonas aeruginosa WH-2

The different isomers of technical-grade hexachlorocyclohexane (t-HCH) including the insecticidal gamma-isomer, commonly known as lindane, have been reported to be toxic, carcinogenic and endocrine disrupters. The spatial arrangements of the chlorine atoms on different isomers and low aqueous phase solubility contribute to their persistence in environment, beta-HCH being the most resistance to transformation. The biosurfactant preparation of Pseudomonas aeruginosa isolate WH-2 was evaluated for its ability to improve the aqueous phase partitioning of different isomers of HCH-muck. Further, the ability of biosurfactant preparation to emulsify HCH and n-hexadecane was checked under different conditions, usually characteristic of sites contaminated with pollutants viz. wide range of pH, temperature, and salinity. The data obtained from this study will be helpful in designing suitable bioremediation strategies for huge stock piles of HCH-muck and sites polluted by reckless use/disposal of HCH-isomers.

Novel characteristics of sophorolipids, yeast glycolipid biosurfactants, as biodegradable low-foaming surfactants

Sophorolipids (SLs) are a family of glycolipid type biosurfactants, which are largely produced by the non-pathogenic yeast, Candida bombicola. In order to investigate the possibility of SLs for industrial use, here we examined the interfacial activities, cytotoxicity and biodegradability of SLs, and compared these properties with those of two lipopeptide type biosurfactants (surfactin and arthrofactin), sodium laurate (soap, SP) and four kinds of chemically synthesized surfactants including two block-copolymer nonionic surfactants (BPs), polyoxyethylene lauryl ether (AE) and sodium dodecyl sulfate (SDS). It was indicated that SLs had extremely low-foaming properties and high detergency comparable with commercially available low-foaming BPs. These interfacial activities of SLs were maintained under 100 ppm water hardness. Cytotoxicity of SLs on human keratinocytes was the same as surfactin, which has already been commercialized as cosmetic material, but higher than BPs. Moreover, biodegradability of SLs using the OECD Guidelines for Testing of Chemicals (301C, Modified MITI Test) displayed that SLs can be classified as "readily" biodegradable chemicals, which are defined as chemicals that are degraded 60% within 28 days under specified test methods. We observed 61% degradation of SLs on the eighth day of cultivation. Our results indicate that SLs are low-foaming surfactants with high detergency, which also exhibit both low cytotoxicity and readily biodegradable properties.

A case study of in situ oil contamination in a mangrove swamp (Rio De Janeiro, Brazil)

Mangroves are sensitive ecosystems of prominent ecological value that lamentably have lost much of their areas across the world. The vulnerability of mangroves grown in proximity to cities requires the development of new technologies for the remediation of acute oil spills and chronic contaminations. Studies on oil remediation are usually performed with in vitro microcosms whereas in situ experiments are rare. The aim of this work was to evaluate oil degradation on mangrove ecosystems using in situ microcosms seeded with an indigenous hydrocarbonoclastic bacterial consortium (HBC). Although the potential degradation of oil through HBC has been reported, their seeding directly on the sediment did not stimulate oil degradation during the experimental period. This is probably due to the availability of carbon sources that are easier to degrade than petroleum hydrocarbons. Our results emphasize the fragility of mangrove ecosystems during accidental oil spills and also the need for more efficient technologies for their remediation.

Mechanism of membrane permeabilization by a bacterial trehalose lipid biosurfactant produced by Rhodococcus sp

The interactions of a succinoyl bacterial trehalose lipid biosurfactant produced by Rhodococcus sp. with phospholipid vesicles, leading to membrane permeabilization, are studied by means of calorimetric and fluorescence and absorption spectroscopical techniques in search for a molecular model. The critical micelle concentration (CMC) of trehalose lipid is determined, by surface tension measurements, to be 300 muM. Binding of trehalose lipid to palmitoyloleoylphosphatidylcholine membranes is studied by means of isothermal titration calorimetry. The partition constant, in conjunction with the CMC, indicates that trehalose lipid behaves as a weak detergent, which prefers membrane incorporation over micellization. Addition of trehalose lipid to palmitoyloleoylphosphatidylcholine large unilamellar vesicles results in a size-selective leakage of entrapped solutes to the external medium. Experimental evidence is provided to support the requirement of a stage of flip-flop prior to membrane permeabilization, and the rate of flip-flop is measured using fluorescent probes assays. The lipid composition of the target membrane is found to modulate the leakage process to a great extent. It is proposed that trehalose lipid incorporates into phosphatidylcholine membranes and segregates within lateral domains which may constitute membrane defects or "pores", through which the leakage of small solutes might take place. The results presented here contribute to the knowledge of the molecular mechanisms underlying the membrane-related biological actions of this bacterial trehalose lipid biosurfactant.

Potential applications of surface active compounds by Gordonia sp. strain BS29 in soil remediation technologies

A wide range of structurally different surface active compounds (SACs) is synthesised by many prokaryotic and eukaryotic microorganisms. Due to their properties, microbial SACs have been exploited in environmental remediation techniques. From a diesel-contaminated soil, we isolated the Gordonia sp. strain BS29 which extensively grows on aliphatic hydrocarbons and produces two different types of SACs: extracellular bioemulsans and cell-bound biosurfactants. The aim of this work was to evaluate the potential applications of the strain BS29 and its SACs in the following environmental technologies: bioremediation of soils contaminated by aliphatic and aromatic hydrocarbons, and washing of soils contaminated by crude oil, polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Microcosm bioremediation experiments were carried out with soils contaminated by aliphatic hydrocarbons or PAHs, while batch soil washing experiments were carried out with soils contaminated by crude oil, PAHs or heavy metals. Bioremediation results showed that the BS29 bioemulsans are able to slightly enhance the biodegradation of recalcitrant branched hydrocarbons. On the other hand, we obtained the best results in soil washing of hydrocarbons. The BS29 bioemulsans effectively remove crude oil and PAHs from soil. Particularly, crude oil removal by BS29 bioemulsans is comparable to the rhamnolipid one in the same experimental conditions showing that the BS29 bioemulsans are promising washing agents for remediation of hydrocarbon-contaminated soils.

In situ detection of the intermediates in the biosynthesis of surfactin, a lipoheptapeptide from Bacillus subtilis OKB 105, by whole-cell cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in combination with mutant analysis

An innovative technique to investigate the intermediates involved in the biosynthesis of the lipoheptapeptide surfactin from Bacillus subtilis OKB105 combining whole-cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) with targeted generation of knock-out mutants was demonstrated. This method allows efficient, sensitive detection of biosynthetic intermediates in a minimum of time directly at the outer surface of microbial cells picked from agar plates or in surface extracts prepared thereof. Biosynthesis of surfactin is encoded by the srf-operon which is organized into four open reading frames which have been attributed to three multifunctional NRPS enzymes (SrfA-C) and a thioesterase/acyltransferase enzyme SrfD. For the wild-type strain OKB 105 only the end product surfactin was found mass spectrometrically. For the detection of lipopeptide intermediates three plasmid- and transposon-insertion mutants were generated interrupting the surfactin assembly line at defined positions. Strain LAB 327 was mutated in the spacer region between enzymes SrfA and B. Here only SrfA was active with the lipotripeptide beta-OH-acyl-L-Glu-L-Leu-D-Leu as the end product. Mutant OKB 120 bears a transposon mutation in SrfB between the first and second amino acid activating modules SrfB1 and SrfB2. It showed all intermediates from the lipodi- until to the lipotetrapeptide beta-OH-acyl-L-Glu-L-Leu-D-Leu-L-Val. In LAB 223 SrfC was knocked out by a transposon mutation. It produced the lipohexapeptide beta-OH-acyl-L-Glu-L-Leu-D-Leu-L-Val-L-Asp-D-Leu. Our work highlights the applicability and the potential of whole-cell MALDI-TOFMS as an innovative efficient tool for the analysis of intermediate steps of biosynthetic pathways.

Antimicrobial activity of the iron-sulfur nitroso compound Roussin's black salt [Fe4S3(NO)7] on the hyperthermophilic archaeon Pyrococcus furiosus

The iron-sulfur nitroso compound [Fe(4)S(3)(NO)(7)](-) is a broad-spectrum antimicrobial agent that has been used for more than 100 years to combat pathogenic anaerobes. Known as Roussin's black salt (RBS), it contains seven moles of nitric oxide, the release of which was always assumed to mediate its cytotoxicity. Using the hyperthermophilic archaeon Pyrococcus furiosus, it is demonstrated through growth studies, membrane analyses, and scanning electron microscopy that nitric oxide does not play a role in RBS toxicity; rather, the mechanism involves membrane disruption leading to cell lysis. Moreover, insoluble elemental sulfur (S(0)), which is reduced by P. furiosus to hydrogen sulfide, prevents cell lysis by RBS. It is proposed that S(0) also directly interacts with the membranes of P. furiosus during its transfer into the cell, ultimately for reduction by a cytosolic NADPH sulfur reductase. RBS is proposed to be a new class of inorganic antimicrobial agent that also has potential use as an inert cell-lysing agent.

Evaluation of screening methods for demulsifying bacteria and characterization of lipopeptide bio-demulsifier produced by Alcaligenes sp

In this paper, surface tension measurement, oil-spreading test and blood-plate hemolysis test were attempted in the screening of demulsifying bacteria. After the comparison to the screening results obtained in demulsification test, 50 mN/m of surface tension of culture was proposed as a preliminary screening standard for potential demulsifying bacteria. For the identification of efficient demulsifying strains, surface tension level was set at 40 mN/m. The detected strains were further verified in demulsification test. Compared to using demulsification test alone as screening method, the proposed screening protocol would be more efficient. From the screening, a highly efficient demulsifying stain, S-XJ-1, was isolated from petroleum-contaminated soil and identified as Alcaligenes sp. by 16S rRNA gene and physiological test. It achieved 96.5% and 49.8% of emulsion breaking ratio in W/O and O/W kerosene emulsion within 24h, respectively, and also showed 95% of water separation ratio in oilfield petroleum emulsion within 2h. The bio-demulsifier was found to be cell-wall combined. After soxhlet extraction and purification through silicon-gel column, the bio-demulsifier was then identified as lipopeptide biosurfactant by TLC and FT-IR.

Isolation and characterization of a C12-lipopeptide produced by Bacillus subtilis HSO 121

A new lipopeptide with C12 fatty acid has been isolated from the cell broth of Bacillus subtilis HSO121 by chromatographic methods, which is believed to be the homologue of lipopeptides. The fatty acid portion was methylated and analyzed by GC/MS, ESI Q-TOF MS and 1H-NMR. The peptide portion, of which the amino acid composition was obtained by HPLC combined with a phenyl isothiocyanate (PITC) derivatization methods, was analyzed by ESI Q-TOF MS. Comparing the obtained results with surfactin C13 showed that the new lipopeptide has a peptide moiety similar to that of surfactin and the difference exists in the fatty acid portion, which is an iso-C12 beta-hydroxy fatty acid. The critical micelle concentration (CMC) of this new homologue is estimated to be 6.27 x 10(-5) mol/l in 10 mmol/l phosphate buffer solution (PBS, pH 8.0) at 30 degrees C, and the surface tension at CMC (gamma CMC) achieved is as little as 27.71 mN/m. The hemolytic activities of the C12-lipopeptide on 2% human erythrocytes showed a HC50 of 26.5 micromol/l.

Mannosylerythritol lipids: a review

Mannosylerythritol lipids (MELs) are surface active compounds that belong to the glycolipid class of biosurfactants (BSs). MELs are produced by Pseudozyma sp. as a major component while Ustilago sp. produces them as a minor component. Although MELs have been known for over five decades, they recently regained attention due to their environmental compatibility, mild production conditions, structural diversity, self-assembling properties and versatile biochemical functions. In this review, the MEL producing microorganisms, the production conditions, their applications, their diverse structures and self-assembling properties are discussed. The biosynthetic pathways and the regulatory mechanisms involved in the production of MEL are also explained here.

Dielectric properties tangential to the interface in model insoluble monolayers: theoretical assessment

Studies of insoluble monolayers built of phospholipids and various long-chained fatty acids or their glycerin esters are the major source for what is currently known about the relationship between monolayer composition and physicochemical properties. The surface pressure, dipole moment, dielectric permittivity, polarizability, refractivity, and other electrical and optical features are governed by the surfactant structural specificity and solvent organization at the microscopic level. To provide insight into the atomistic details of the interfacial structure, model monolayers at the air/water interface of two distinctly different in composition and isotherm profile surfactants are investigated by means of molecular dynamics all-atom simulations. Analysis of the computational results allows the estimation of empirically unattainable quantities such as tangential (di)electric properties, their decomposition to surfactant and water contributions, and their relationship with the changes in interfacial molecular organization at different surface concentrations. The employed theoretical approach provides a comprehensive description of interfacial phenomena at the molecular level where the traditional phenomenological investigations are ineffective.

Molecular characterization of surfactant-driven microbial community changes in anaerobic phenanthrene-degrading cultures under methanogenic conditions

SDS and Triton X-100 added at their critical micelle concentrations (CMCs), increased phenanthrene solubility in the presence of sediments and inhibited phenanthrene biodegradation. Triton X-100 caused more inhibition than SDS. 16S rDNA analyses revealed that both surfactants changed the microbial communities of phenanthrene-degrading cultures. Further, after the surfactant additions, parts of the microbial populations were not detected and methane production decreased. Surfactant applications, necessary to achieve actual CMCs, alter microbial community structure and diminish methanogenic activity under anaerobic conditions. We propose that this change may be related to the inhibitory effects of SDS and Triton X-100 on phenanthrene biodegradation under methanogenic conditions.

Baby Shampoo Nasal Irrigations for the Symptomatic Post-functional Endoscopic Sinus Surgery Patient

Background

Symptoms of postnasal drainage and thickened mucus are commonly seen in patients with chronic rhinosinusitis (CRS) recalcitrant to sinus surgery and conventional medical therapies. Chemical surfactants can act as a mucolytic by reducing water surface tension and have the potential to serve as an antimicrobial agent. Baby shampoo is an inexpensive, commercially available solution containing multiple chemical surfactants. This is an in vitro study of its antimicrobial effects on Pseudomonas biofilms with translation to a clinical study for use as an adjuvant nasal wash in patients with CRS who remain symptomatic despite adequate sinus surgery and conventional medical therapies.

Methods

In vitro testing was performed to determine the optimal concentration of baby shampoo that disrupted preformed bacterial biofilms and inhibited biofilm formation. This concentration was then used in a prospective study of symptomatic post–functional endoscopic sinus surgery (FESS) patients who irrigated twice a day for 4 weeks. Validated outcome forms and objective smell testing was performed before and after therapy.

Results

One percent baby shampoo in normal saline was the optimal concentration for inhibition of Pseudomonas biofilm formation. Baby shampoo had no effect on the eradication of preformed Pseudomonas biofilms. Eighteen patients with CRS with an average of 2.8 surgeries were studied after irrigating with 1% baby shampoo solution. Two patients discontinued use because of minor nasal and skin irritations; 46.6% of patients experienced an overall improvement in their subjective symptoms, and 60% of patients noted improvement in specific symptoms of thickened mucus and postnasal drainage.

Conclusion

Baby shampoo nasal irrigation has promise as an inexpensive, tolerable adjuvant to conventional medical therapies for symptomatic patients after FESS. Its greatest benefit may be in improving symptoms of thickened nasal discharge and postnasal drainage.

Insecticidal activity of caffeine aqueous solutions and caffeine oleate emulsions against Drosophila melanogaster and Hypothenemus hampei

The bioactivity of caffeine aqueous solutions (0.20-2.00 wt %) and caffeine oleate emulsions (20 vol % oil, 2.00 wt % surfactant, 0.04 wt % caffeine, 0.05 wt % oleic acid) was assessed against two biological models: Drosophila melanogaster and Hypothenemus hampei. The caffeine aqueous solutions showed no insecticidal activity, whereas caffeine oleate emulsions had high bioactivity against both D. melanogaster and H. hampei. By preparing the caffeine oleate emulsions with anionic surfactants (i.e., sodium lauryl sulfate, sodium laureate, and sodium oleate), we obtained a lethal time 50 (LT50) of 23 min. In the case of caffeine oleate emulsions prepared with nonionic surfactants (i.e., Tween 20 and Tween 80), a LT50 of approximately 17 min was observed. The high bioactivity of the caffeine oleate emulsion against H. hampei opens the possibility of using this insecticide formulation as an effective way to control this pest that greatly affects coffee plantations around the world.

Bacterial metabolism of long-chain n-alkanes

Degradation of alkanes is a widespread phenomenon in nature, and numerous microorganisms, both prokaryotic and eukaryotic, capable of utilizing these substrates as a carbon and energy source have been isolated and characterized. In this review, we summarize recent advances in the understanding of bacterial metabolism of long-chain n-alkanes. Bacterial strategies for accessing these highly hydrophobic substrates are presented, along with systems for their enzymatic degradation and conversion into products of potential industrial value. We further summarize the current knowledge on the regulation of bacterial long-chain n-alkane metabolism and survey progress in understanding bacterial pathways for utilization of n-alkanes under anaerobic conditions.