Nelly Christova

Biosurfactant Production By A New Pseudomonas Putida Strain

Observation of both tensio-active and emulsifying activities indicated that biosurfactants were produced by the newly isolated and promising strain Pseudomonas putida 21BN. The biosurfactants were identified as rhamnolipids, the amphiphilic surface-active glycolipids usually secreted by Pseudomonas spp. Their production was observed when the strain was grown on soluble substrates, such as glucose or on poorly soluble substrates, such as hexadecane, reaching values of 1.2 g l-1. When grown on hexadecane as the sole carbon source the biosurfactant lowered the surface tension of the medium to 29 mN m-1 and formed stable and compact emulsions with emulsifying activity of 69%

Production and structural elucidation of trehalose tetraesters (biosurfactants) from a novel alkanothrophic Rhodococcus wratislaviensis strain

Aims:  To isolate a biosurfactant‐producing bacterial strain and to identify and characterize the chemical structure and properties of its biosurfactants.

Rhamnolipid biosurfactants produced by Renibacterium salmoninarum 27BN during growth on n-hexadecane.

A new strain Renibacterium salmoninarum 27BN was isolated for its capacity to utilize nhexadecane as sole substrate. Growth on n-hexadecane was accompanied with the production of glycolipid surface active substances detected by surface pressure lowering and emulsifying activity. Glycolipid detection by thin layer chromatography and infrared spectra analyses showed for the first time that Renibacterium salmoninarum 27BN secretes the two rhamnolipids RLL and RRLL typical for Pseudomonas aeruginosa. Growth of Renibacterium salmoninarum 27BN on n-hexadecane depended on the bioavailability of the substrate and the secreted rhamnolipids appeared to be efficient in increasing hexadecane availability for the cells.

Naphthalene degradation and biosurfactant activity by Bacillus cereus 28BN.

Biosurfactant activity and naphthalene degradation by a new strain identified as Bacillus cereus 28BN were studied. The strain grew well and produced effective biosurfactants in the presence of n-alkanes, naphthalene, crude oil and vegetable oils. The biosurfactants were detected by the surface tension lowering of the medium, thin layer chromatography and infrared spectra analysis. With (2%) naphthalene as the sole carbon source, high levels of rhamnolipids at a concentration of 2.3 g l-1 were determined in the stationary growth. After 20 d of incubation 72 ± 4% of the initial naphthalene was degraded. This is the first report for a Bacillus cereus rhamnolipid producing strain that utilized naphthalene under aerobic conditions. The strain looks promising for application in environmental technologies.

Enhanced hydrocarbon biodegradation by a newly isolated Bacillus subtilis strain.

The relation between hydrocarbon degradation and biosurfactant (rhamnolipid) production by a new Bacillus subtilis 22BN strain was investigated. The strain was isolated for its capacity to utilize n-hexadecane and naphthalene and at the same time to produce surfaceactive compound at high concentrations (1.5 -2.0 g l-1). Biosurfactant production was detected by surface tension lowering and emulsifying activity. The strain is a good degrader of both hydrocarbons used with degradability of 98.3 ± 1% and 75 ± 2% for n-hexadecane and naphthalene, respectively. Measurement of cell hydrophobicity showed that the combination of slightly soluble substrate and rhamnolipid developed higher hydrophobicity correlated with increased utilization of both hydrocarbon substrates. To our knowledge, this is the first report of Bacillus subtilis strain that degrades hydrophobic compounds and at the same time produces rhamnolipid biosurfactant.

Dependence of yeast permeabilization with Triton X-100 on the cell age

Acid phosphatase activity and protein release were determined in cell suspensions ofYarrowia lipolytica andTorulospora delbrueckii at different stages of their growth by permeabilization with Triton X-100. The effect of the surfactant on the cell permeability did not depend on the cell age.

Chemical Characterization and Physical and Biological Activities of Rhamnolipids Produced by Pseudomonas aeruginosa BN10

Pseudomonas aeruginosa BN10 isolated from hydrocarbon-polluted soil was found to produce rhamnolipids when cultivated on 2% glycerol, glucose, n-hexadecane, and n-alkanes. The rhamnolipids were partially purified on silica gel columns and their chemical structures elucidated by combination of one- and two-dimensional 1H and 13C NMR techniques and ESI-MS analysis. Eight structural rhamnolipid homologues were identified: Rha-C10- C8, Rha-C10-C10, Rha-C10-C12:1, Rha-C10-C12, Rha2-C10-C8, Rha2-C10-C10, Rha2-C10-C12:1, and Rha2-C10-C12. The chemical composition of the rhamnolipid mixtures produced on different carbon sources did not vary with the type of carbon source used. The rhamnolipid mixture produced by Pseudomonas aeruginosa BN10 on glycerol reduced the surface tension of pure water from 72 to 29 mN m-1 at a critical micellar concentration of 40 mg l-1, and the interfacial tension was 0.9 mN m-1. The new surfactant product formed stable emulsions with hydrocarbons and showed high antimicrobial activity against Gram-positive bacteria. The present study shows that the new strain Pseudomonas aeruginosa BN10 demonstrates enhanced production of the di-rhamnolipid Rha2-C10-C10 on all carbon sources used. Due to its excellent surface and good antimicrobial activities the rhamnolipid homologue mixture from Pseudomonas aeruginosa BN10 can be exploited for use in bioremediation, petroleum and pharmaceutical industries.

Purification and Properties of Alkaline Phosphatase with Protein Phosphatase Activity from Saccharomyces cerevisiae

Abstract An alkaline phosphatase (ALPase) from Saccharomyces cerevisiae strain 257 was purified 345-fold with specific activity of 54 533 nmol × min−1 × mg protein−1 . It was shown to be a dimeric protein (apparent mol. wt. approx. 130 kDa) with optimum activity at pH 8.6 - 8.8 and good stability at 50 °C. The ALPase was a non-specific enzyme hydrolyzing a wide variety of monophosphate esters. The enzyme showed protein phosphatase activity and this activity was not Mg2+ - dependent in contrast to p-nitrophenyl phosphate (pNPP) activity. The Km value for pNNP hydrolysis was determined to be 2.2 × 10−5 м. Orthophosphate inhibited the enzyme in a competitive mode with the Ki of 2.3 x 10−4 м. Phosphate transfer of the ALPase is almost zero with all alcohols tested except for Tris.

Phosphorylase Phosphatase Activity in Saccharomyces cerevisiae 257

Abstract Phosphorylase Phosphatase, Protein Phosphatase, Saccharomyces cerevisiae Aphosphatase, active towards phosphorylase a and phosphorylated proteins casein and histone II-A , was isolated from Saccharomyces cerevisiae 257. The enzyme dephosphorylated glycogen phosphorylase from commercial yeast rendering it inactive. The protein phosphatase activity was not influenced by any metal ions. Phosphorylase phosphatase activity was slightly stimulated by p -nitrophenyl phosphate and inhibited by heparin.

New Approach for n-Hexadecane Biodegradation by Sol-Gel Entrapped Bacterial Cells

Abstract In this study sol-gel hybrid materials in the system SiO2-chitosan (CS) - polyethylene glycol (PEG), as novel structures with potential application in bioremediation were investigated. The organic components - CS and PEG were used as structural modifiers for functionality improvement. The catabolic activity to n-hexadecane of Pseudomonas aeruginosa BN10 free and immobilized cells was estimated. The cell immobilization technique was employed to evaluate its efficiency on biodegradation and protective effect from high levels of hydrocarbons. The characteristics of obtained hybrid materials were investigated via X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Atomic-force microscopy (AFM) analyses. The obtained results revealed that the organic part in the synthesized hybrids is important for microstructure and defined properties creation. The rate of n-hexadecane mineralization by the bacterial strain was influenced by variation in cell densities applied in the immobilization procedures. Semi-continuous processes with multiple xenobiotic supplies were carried out. The synthesized by the sol-gel method hybrid matrices proved to be suitable carriers for realizing an effective biodegradation process of n-hexadecane by Pseudomonas aeruginosa BN10. Biodegradation of 50 kg/m3 of n-hexadecane was realized by free cells. Significantly greater quantity (150 kg/m3) was mineralized for 15 active cycles by entrapped bacterial cells. Biodegradation process with gradual increase of xenobiotic concentration reaching 30 kg/m3 for 120 h was also accomplished.