Evaluation in the performance of the biodegradation of herbicide diuron to high concentrations by Lysinibacillus fusiformis acclimatized by sequential batch culture.

We evaluated and characterized the biodegradation of the herbicide diuron in its commercial form above its saturation concentration by Lysinibacillus fusiformis acclimatized by sequential batch culturing. Acclimatization was carried out in eight cycles in liquid culture, improving the capacity of L. fusiformis to remove diuron from 55.13 ± 1.3% in the first batch to 87.2 ± 0.11% in the eighth batch. Diuron biosorption was characterized with Langmuir and Freundlich isotherms, obtaining a maximum biosorption (qmax) of 0.00885 mg mg-1. In diuron biodegradation assays, a consumption substrate biomass yield (YSD/X) of 6.266 mg mg-1 was obtained, showing that biodegradation was the main mechanism in diuron removal. Diuron biodegradation by L. fusiformis was characterized by the Monod model, with a maximum specific growth rate (µmax) of 0.0245 h-1 and an affinity constant (KSD) of 344.09 mg L-1. A low accumulation of 3,4-dichloroaniline with the production of chloride ions indicated dechlorination when diuron was present at high concentrations. A phytotoxic assay conducted with Lactuca sativa showed that the toxicity of an effluent with diuron at 250 mg L-1 decreased when it was pretreated with acclimatized L. fusiformis. Acclimatization by sequential batch culturing improved the ability of L. fusiformis to biodegrade diuron at high concentrations, showing potential in the bioremediation of diuron-contaminated sites.

Whole-cell bioconversion of naringenin to high added value hydroxylated compounds using Yarrowia lipolytica 2.2ab in surface and liquid cultures.

The bioconversion process of bioactive naringenin by whole-cells of Yarrowia lipolytica 2.2ab for the production of increased value-added compounds is successfully achieved in surface and liquid cultures. This approach is an alternative to the commercial production of these bioactive compounds from vegetable sources, which are limited due to their low concentrations and the complexity of the purification processes. The experimentation rendered seven value-added compounds in both surface and liquid bioconversion cultures. Some of the compounds produced have not been previously reported as products from the bioconversion processes, such as the case of ampelopsin. Biosynthetic pathways were suggested for the naringenin bioconversion using whole-cells of Y. lipolytica 2.2ab. Finally, the extracts obtained from the naringenin bioconversion in liquid cultures showed higher percentage of inhibition of DPPH· and ABTS· radicals up to 32.88 and 2.08 times, respectively, compared to commercial naringenin.

Stable bioemulsifiers are produced by Acinetobacter bouvetii UAM25 growing in different carbon sources.

Acinetobacter species are identified as producing surface-active and emulsifying molecules known as bioemulsifiers. Production, characterization and stability of bioemulsifiers produced by Acinetobacter bouvetii UAM25 were studied. A. bouvetii UAM25 grew in three different carbon and energy sources: ethanol, a glycerol-hexadecane mixture and waste cooking oil in an airlift bioreactor, showing that bioemulsifier production was growth associated. The three purified bioemulsifiers were lipo-heteropolysaccharides of high molecular weight (4866 ± 533 and 462 ± 101 kDa). The best carbon source and energy for bioemulsifier production was wasted cooking oil, with a highest emulsifying capacity (76.2 ± 3.5 EU mg-1) as compared with ethanol (46.6 ± 7.1 EU mg-1) and the glycerol-hexadecane mixture (49.5 ± 4.2 EU mg-1). The three bioemulsifiers in our study displayed similar macromolecular structures, regardless of the nature (hydrophobic or hydrophilic) of the carbon and energy source. Bioemulsifiers did not decrease surface tension, but the emulsifying capacity of all of them was retained under extreme variation in salinity (0-50 g NaCl L-1), pH (3-10) and temperature (25-121 °C), indicative of remarkable stability. These findings contribute to understanding of the relationship between: production, physical properties, chemical composition and stability of bioemulsifiers for their potential applications in biotechnology, such as bioremediation of hydrocarbon-contaminated soil and water.

Kinetic Constants for Biological Ammonium and Nitrite Oxidation Processes Under Sulfide Inhibition.

Inhibition of nitrification by sulfide was assessed using sludge obtained from a steady-state nitrifying reactor. Independent batch activity assays were performed with ammonium and nitrite as substrate, in order to discriminate the effect of sulfide on ammonium and nitrite oxidation. In the absence of sulfide, substrate affinity constants (K S,NH4 = 2.41 ± 0.11 mg N/L; K s, NO2 = 0.74 ± 0.03 mg N/L) and maximum specific rates (q max,NH4 = 0.086 ± 0.008 mg N/mg microbial protein h; q max,NO2 = 0.124 ± 0.001 mg N/mg microbial protein h) were determined. Inhibition of ammonium oxidation was no-competitive (inhibition constant (K i , NH4 ) of 2.54 ± 0.12 mg HS(-)-S/L) while inhibition of nitrite oxidation was mixed (competitive inhibition constant (K' i , NO2 ) of 0.22 ± 0.03 mg HS(-)-S/L and no-competitive inhibition constant (K i , NO2 ) of 1.03 ± 0.06 mg HS(-)-S/L). Sulfide has greater inhibitory effect on nitrite oxidation than ammonium oxidation, and its presence in nitrification systems should be avoided to prevent accumulation of nitrite. By simulating the effect of sulfide addition in a continuous nitrifying reactor under steady-state operation, it was shown that the maximum sulfide concentration that the sludge can tolerate without affecting the ammonium consumption efficiency and nitrate yield is 1 mg HS(-)-S/L.

Production of thermostable lipase by Thermomyces lanuginosus on solid-state fermentation: selective hydrolysis of sardine oil.

A naturally immobilized biocatalyst with lipase activity was produced by Thermomyces lanuginosus on solid-state fermentation with perlite as inert support. Maxima lipase activities (22 and 120 U/g of dry matter, using p-nitrophenyl octanoate and trioctanoine, respectively, as substrates) were obtained after 72 h of solid culture, remaining nearly constant up to 120 h. Maxima lipase activity was found at 60 to 85 °C and pH 10. The biocatalyst was stable at 60 °C for at least 4 h of incubation and a pH from 7 to 10. Energy values of activation and deactivation of lipase were of 26 and 6.7 kJ/mol, respectively. The biocatalyst shows high selectivity for the release of the omega-3 polyunsaturated fatty acids, eicosapentaenoic (EPA) and docosahexaenoic acids (DHA), during the hydrolysis of sardine oil. The EPA/DHA ratio (16:6) released by this biocatalyst was superior to that obtained with the commercial preparations of T. lanuginosus.

Assessment of the limiting step of mass transfer in n-hexadecane biodegradation in a bubble column reactor.

A mathematical model was developed to assess limiting step of mass transfer in the n-hexadecane (HXD) biodegradation by a microbial consortium. A double Monod kinetic (oxygen and HXD) for biomass production was successfully used to describe the experimental data. Good fitting (r²=0.92) between the model solution and experimental data was obtained. The overall mass transfer coefficients for HXD, k(L)a(HXD), and oxygen, k(L)a(O2), were experimentally determined and biosurfactant production was indirectly determined through surface tension measurements in the aqueous phase. It was observed that a surface tension reduction from 65 (0 h of culture) to 47 mN m⁻¹ (240 h of culture) was related to a decrease of 52% in the HXD droplet diameter and to an increase of 63% in k(L)a(HXD), respect the initial values. Conversely, k(L)a(O2) was repressed up to 37% compared to the initial value. The maximum rate analysis based on the mathematical model showed that HXD transfer was up to 5-fold lower than its consumption. On the contrary, oxygen transfer was always higher than its consumption. Thus, the limiting step under the working conditions was the HXD transfer to the aqueous phase. However, slight reductions in k(L)a(O2) could result in oxygen transfer limitations during the last 60 h of the cultures.

Physiological, morphological, and mannanase production studies on Aspergillus niger uam-gs1 mutants

Mutant strains from Aspergillus niger UAM-GS1 were produced by UV radiation to increase their hemicellulolytic and cellulolytic activity production. The mutant strains showing more enzymatic activity were those labelled GS1-S059 and GS1-S067. These strains also showed the largest relationship between diameter of hydrolysis zone and colony diameter. The mutant GS1-S067 showed a colony radial extension rate and a biomass growth rate g biomass/(cm² h), 1.17 times higher than that achieved by strain UAM-GS1. The high invasive capacity makes this mutant strain a promising alternative for its use in solid substrate fermentation (SSF). The morphological properties of the two mutant strains were evaluated by using scanning electron microscopy. The diameter of the sporangium of the mutant strains GS1-S059 and GS1-S067 was significantly larger (P < 0.05) than that found for the parental strain. The hypha length and diameter of the mutant strains significantly changed (P < 0.05) compared to the parental strain. A Pearson correlation analysis on hypha length, sporangium diameter, and cellulase and xylanase activities indicated that there was a strong relationship among these variables in relation to mannanase activity. Mutant strains GS1-S059 and GS1-S067 significantly increased their level of mannanase, xylanase and cellulase production, compared to the parental strain, improving their potential industrial applications.