Permeabilization of yeast cells (Kluyveromyces lactis) with organic solvents

Dielectric constants of organic pollutants determine their strength for enhancing microbial iron reduction

Physicochemical properties are essential characteristics of organic compounds, which not only impact the fate of organic pollutants but also determine their application in biological processes. Here, we first found that the dielectric constants (ɛ) of organic pollutants negatively correlated to their strength for enhancing microbial Fe(III) reduction. Those with lower ɛ values than 2.61 potentially promoted the above process following the sequence carbon tetrachloride (CT) > benzene > toluene > tetrachloroethylene (PCE) due to their different ability to deprotonate the phosphorus-related groups on the outer cell membrane of iron-reducing bacteria Shewanella oneidensis MR-1 (MR-1). The stronger deprotonation of phosphorus-related groups induced more negative charge of cell surface and more strongly increased cell membrane permeability and consequently stimulated faster release of flavin mononucleotide (FMN) as an electron shuttle/cofactor for Fe(III) reduction. These findings are significant for understanding the biogeochemistry in multi-organic contaminated subsurface and providing knowledge for remediation strategies and current production.

Purified lactases versus whole-cell lactases-the winner takes it all

Lactose-free dairy products are in great demand worldwide due to the high prevalence of lactose intolerance. To make lactose-free dairy products, commercially available β-galactosidase enzymes, also termed lactases, are used to break down lactose to its constituent monosaccharides, glucose and galactose. In this mini-review, the characteristics of lactase enzymes, their origin, and ways of use are discussed in light of their potential for hydrolyzing lactose. We also discuss whole-cell lactase catalysts, which appear to have great potential in terms of cost reduction and convenience, and which are more natural alternatives to purified enzymes. Lactic acid bacteria (LAB) already used in food fermentations seem to be optimal candidates for whole-cell lactases. However, they have not been industrially exploited yet due to technical hurdles. For whole-cell lactases to be efficient, the lactase enzymes inside the cells must be made available for lactose hydrolysis, and thus, cells need to be permeabilized or disrupted prior to use. Here we review state-of-the-art approaches for disrupting or permeabilizing microorganisms. Lastly, based on recent scientific achievements, we propose a novel, resource-efficient, and low-cost scenario for achieving lactose hydrolysis at a dairy plant using a LAB whole-cell lactase.Key points• Lactases (β-galactosidase) are essential for producing lactose-free dairy products• Novel permeabilization techniques facilitate the use of LAB lactases• Whole-cell lactase catalysts have great potential for reducing costs and resources Graphical abstract.

Bifacial biological effects of ethanol: acetaldehyde production by oral Streptococcus species and the antibacterial effects of ethanol against these bacteria

Background:Many previous studies have focused on the acetaldehyde produced from ethanol by oral bacteria as a risk factor for oral cancer. Most of these studies involved low ethanol concentrations (ca. 10 mM), but oral bacteria are exposed to a wide range of ethanol concentrations (100–10,000 mM) when alcoholic beverages are consumed. In contrast, ethanol is widely used at high concentrations (> 5,000 mM) as an antiseptic/disinfectant, suggesting that ethanol has bifacial biological effects; i.e. it acts as both a metabolic substrate for bacterial acetaldehyde production and an antimicrobial agent.

Materials and methods:We examined the acetaldehyde production from ethanol by oral streptococci and the effects of ethanol exposure on the growth and viability of these bacteria at a wide range of ethanol concentrations (10–10,000 mM).

Results:Acetaldehyde production was the highest at an ethanol concentration of 2,000 mM (2.1–48-fold higher than that seen at an ethanol concentration of 10 mM). Bacterial growth was inhibited by > 1,000 mM of ethanol, and the bacteria did not seem viable in the presence of > 5,000 mM of ethanol, although they still produced acetaldehyde.

Conclusion:Ethanol has bifacial biological effects, and the concentration ranges of these effects overlap.

Extracción de sustancias bioactivas de <i>Pleurotus ostreatus</i> (Pleurotaceae) por maceración dinámica

La extracción de compuestos bioactivos de Pleurotus ostreatus por maceración dinámica, es un proceso sencillo y económico, que normalmente presenta baja eficiencia. El objetivo de este trabajo fue evaluar el proceso de extracción para determinar qué tratamiento permite la mayor eficiencia, analizando la influencia de los factores de estudio: concentración de etanol (50 %, 80 %, 95 %) y relación sólido/solvente (1:10, 1:20, 1:30). Se maceraron 5 g de polvo fúngico en etanol acuoso durante 90 minutos, a 150 rpm, 25 °C y tamaño de partícula de 0,5 a 1,0 mm. Se trataron los datos mediante estadística paramétrica con un nivel de confianza del 95 %. Los resultados revelaron que la mayor eficiencia de extracción total (40,9 %) en base seca se obtuvo con etanol al 50 % y una relación sólido/solvente de 1:30. Por componentes se encontró que, el etanol al 50 % con una relación de 1:20 permitió la máxima eficiencia para carbohidratos totales (17,9 %) y polisacáridos (17,2 %), mientras que con una relación de 1:30 se obtuvo la máxima eficiencia para azúcares reductores (0,91 %) y polifenoles (0,23 %). Por otro lado, el etanol al 95 % y la relación 1:30 permitió la máxima eficiencia para proteínas (29,4 %). La extracción de beta-glucanos no fue significativa. La eficiencia de la extracción está muy influenciada por los parámetros de operación, principalmente por la concentración de etanol; en particular, la de 50 % resultó más favorable para la obtención de la mayoría de sustancias bioactivas con potencial nutracéutico.

Development of a novel integrated process for co-production of β-galactosidase and ethanol using lactose as substrate

A novel integrated process was developed successfully for co-production of β-galactosidase and ethanol using lactose as substrate, containing fermentation (Kluyveromyces lactis), isolation, permeabilization (a new recycling process) and spray drying. Firstly, a new fed-batch strategy optimized co-produced β-galactosidase at 105.91U/mL and ethanol at 32.16mg/mL, 4.40-fold and 10.82-fold increase over the results from initial conditions, respectively. Then a new mathematic model for the recycling permeabilization was established successfully. As expected, the total cells sediment from isolation of the fed-batch culture was permeabilized completely by distilled ethanol from broth supernatant. More amazedly, the specific activity of β-galactosidase product by spray drying the permeabilized cells reached 2.61U/mg, meeting the demand of commercial products. Furthermore, the ethanol product at 33.8% (v/v) was obtained from the novel integrated process, which could be applied for various applications. To conclude, the novel integrated process might be a feasible strategy to scale up for industrialization.

Directed multistep biocatalysis using tailored permeabilized cells

: Recent developments in the field of biocatalysis using permeabilized cells are reviewed here, with a special emphasis on the newly emerging area of multistep biocatalysis using permeabilized cells. New methods of metabolic engineering using in silico network design and new methods of genetic engineering provide the opportunity to design more complex biocatalysts for the synthesis of complex biomolecules. Methods for the permeabilization of cells are thoroughly reviewed. We provide an extended review of useful available databases and bioinformatics tools, particularly for setting up genome-scale reconstructed networks. Examples described include phosphorylated carbohydrates, sugar nucleotides, and polyketides.

Development of a process for generating three-dimensional microbial patterns amenable for engineering use

We describe in detail a process for generating three-dimensional patterns of microbes on an optimum substrate in such a way that the patterns are amenable for engineering applications.

A versatile and economical method for the release of recombinant proteins from Escherichia coli by 1-propanol cell disruption

Release of enhanced green fluorescent protein from Escherichia coli by 1-propanol cell disruption.

Fabrication of three dimensional patterns of wide dimensional range using microbes and their applications

Inspired by the wound healing property of certain trees, we report a novel microbes based additive process for producing three dimensional patterns, which has a potential of engineering applications in a variety of fields. Imposing a two dimensional pattern of microbes on a gel media and allowing them to grow in the third dimension is known from its use in biological studies. Instead, we have introduced an intermediate porous substrate between the gel media and the microbial growth, which enables three dimensional patterns in specific forms that can be lifted off and used in engineering applications. In order to demonstrate the applicability of this idea in a diverse set of areas, two applications are selected. In one, using this method of microbial growth, we have fabricated microlenses for enhanced light extraction in organic light emitting diodes, where densely packed microlenses of the diameters of hundreds of microns lead to luminance increase by a factor of 1.24X. In another entirely different type of application, braille text patterns are prepared on a normal office paper where the grown microbial colonies serve as braille tactile dots. Braille dot patterns thus prepared meet the standard specifications (size and spacing) for braille books.

Enhanced production of recombinant aspartase of Aeromonas media NFB-5 in a stirred tank reactor

Aspartase gene (aspA) from Aeromonas media NFB-5 was cloned and expressed in Escherichia coli BL21 using pET21b(+) expression vector. Maximum production of aspartase was obtained at shake-flask after 5 h of IPTG (1.5 mM) induction at 37°C and by supplementing the media with KH2PO4 (0.3%, w/v) and K2HPO4 (0.3%, w/v). Further production was investigated at a laboratory scale stirred tank reactor using response surface methodology (RSM). Agitation (130-270 rpm), aeration (0.30-1.70 vvm) and IPTG induction time (3-7 h) was optimized. Optimal levels of agitation (250 rpm), aeration (1.25 vvm) and induction time (6h) were determined by statistical analysis of the experimental data. More than 7-fold increase in recombinant aspartase (1234 U/g wet weight) was observed than the parent strain (172 U/g wet wt). Homogenized immobilized permeabilized recombinant cells (566 mg/g wet cells) produced more L-aspartic acid as compared to permeabilized recombinant free cells (154 mg/g wet cells).

Biotechnological approaches for the value addition of whey

Whey, the liquid remaining after milk fat and casein have been separated from whole milk, is one of the major disposal problems of the dairy industry, and demands simple and economical solutions. In view of the fast developments in biotechnological techniques, alternatives of treating whey by transforming lactose present in it to value added products have been actively explored. Whey can be used directly as a substrate for the growth of different microorganisms to obtain various products such as ethanol, single-cell protein, enzymes, lactic acid, citric acid, biogas and so on. In this review, a comprehensive and illustrative survey is made to elaborate the various biotechnological innovations/techniques applied for the effective utilization of whey for the production of different bioproducts.

Two-phase systems: potential for in situ extraction of microalgal products

Algae are currently used for production of niche products and are becoming increasingly interesting for the production of bulk commodities, such as biodiesel. For the production of these goods to become economically feasible, production costs will have to be lowered by one order of magnitude. The application of two-phase systems could be used to lower production costs. These systems circumvent the costly step of cell harvesting, whilst the product is extracted and prepared for downstream processing. The mechanism of extraction is a fundamental aspect of the practical question whether two-phase systems can be applied for in situ extraction, viz, simultaneous growth, product formation and extraction, or as a separate downstream processing step. Three possible mechanisms are discussed; 1) product excretion 2) cell permeabilization, and 3) cell death. It was shown that in the case of product excretion, the application of two-phase systems for in situ extraction can be very valuable. With permeabilization and cell death, in situ extraction is not ideal, but the application of two-phase systems as downstream extraction steps can be part of a well-designed biorefinery process. In this way, processing costs can be decreased while the product is mildly and selectively extracted. Thus far none of the algal strains used in two-phase systems have been shown to excrete their product; the output has always been the result of cell death. Two-phase systems can be a good approach as a downstream processing step for these species. For future applications of two-phase in situ extraction in algal production processes, either new species that show product excretion should be discovered, or existing species should be modified to induce product excretion.

Optimal selection of organic solvents for biocompatible extraction of beta-carotene from Dunaliella salina

In the aim of beta-carotene biocompatible extraction, toxicity of various pure solvents belonging to different homologous series has been investigated for Dunaliella salina. The results showed that solvents having logP(oct) > 5 or having a molecular weight over 150 g/mol can be considered biocompatible for this microalga. The membrane critical solvent concentration for each series of solvents has been calculated applying Osborne's model, showing that the aliphatic chlorinated hydrocarbon is the most toxic family studied. Mixtures of a biocompatible solvent (decane) with a toxic solvent (CH(2)Cl(2), MEK, MTBE) have been studied. The beta-carotene extraction ability of CH(2)Cl(2)-decane mixture was found six times more efficient than with pure decane. It has been demonstrated that the extraction ability of solvent depends on its affinity with the product extracted and on its concentration incorporated in the cellular membrane.

Production of L-carnitine by secondary metabolism of bacteria

The increasing commercial demand for L-carnitine has led to a multiplication of efforts to improve its production with bacteria. The use of different cell environments, such as growing, resting, permeabilized, dried, osmotically stressed, freely suspended and immobilized cells, to maintain enzymes sufficiently active for L-carnitine production is discussed in the text. The different cell states of enterobacteria, such as Escherichia coli and Proteus sp., which can be used to produce L-carnitine from crotonobetaine or D-carnitine as substrate, are analyzed. Moreover, the combined application of both bioprocess and metabolic engineering has allowed a deeper understanding of the main factors controlling the production process, such as energy depletion and the alteration of the acetyl-CoA/CoA ratio which are coupled to the end of the biotransformation. Furthermore, the profiles of key central metabolic activities such as the TCA cycle, the glyoxylate shunt and the acetate metabolism are seen to be closely interrelated and affect the biotransformation efficiency. Although genetically modified strains have been obtained, new strain improvement strategies are still needed, especially in Escherichia coli as a model organism for molecular biology studies. This review aims to summarize and update the state of the art in L-carnitine production using E. coli and Proteus sp, emphasizing the importance of proper reactor design and operation strategies, together with metabolic engineering aspects and the need for feed-back between wet and in silico work to optimize this biotransformation.

Configuration of a bioreactor for milk lactose hydrolysis

Permeabilized microbial cells can be used as a crude enzyme preparation for industrial applications. Immobilization and process recycling can compensate for the low specific activity of this preparation. For biomass immobilization, the common support is alginate beads; however, its low surface area and the low biomass concentration limit the activity. We here describe a biocatalyst consisting of a paste of permeabilized Kluyveromyces lactis cells gelled with manganese alginate over a semicircular stainless steel screen. A ratio of wet permeabilized biomass to alginate of 50:4 (wt/wt) resulted in a paste with maximum immobilized beta-galactosidase activity and maximum gel biomass retention. The biocatalysts retained activity better when stored in milk at 4 degrees C than in 50% glycerol. The unused biocatalysts stored in milk did not lose activity after 50 d. However, repeated use of the same biocatalyst 40 times resulted in almost 50% loss of activity. A bioreactor design with two different conditions of operation were tested for milk lactose hydrolysis using this biocatalyst. The bioreactor was operated at 40 degrees C as packed bed or with recirculation, similar to a continuous stirred tank reactor. The continuous system with recirculation resulted in 82.9% lactose hydrolysis at a residence time of 285.5 min (flow of 2.0 ml/min), indicating the potential of this system for processing low lactose milk, or even in processing other substrates, using an appropriate biocatalyst.

Biokinetic models for representing the complete inhibition of microbial activity at high substrate concentrations

This paper reintroduces the Wayman and Tseng model for representing substrate inhibition effects on specific growth rate by further documenting its potential predictive capabilities. It also introduces a modification to this model in which an Andrews inhibition function is used in place of the Monod noninhibitory substrate function. This modification better represents the relationship between specific growth rate and substrate concentration for those substrates that show Andrews type inhibition at lower substrate concentrations, rather than the Monod type noninhibitory behavior described in the model of Wayman and Tseng. Results from nonlinear, least squares regression analysis are used to evaluate the ability of these models to empirically represent experimental data (both new and from the literature). The statistical goodness of fit is evaluated by comparing the regression results against those obtained using other empirical models. Finally, possible mechanisms of toxicity responsible for the observed inhibition trends are used to further justify use of these empirical models. The dominant mechanism considered to be relevant for conceptually explaining complete inhibition at high concentrations of solvents is the deterioration of cell membrane integrity. Literature citations are used to support this argument. This work should lead to improvements in the mathematical modeling of contaminant fate and transport in the environment and in the simulation of microbial growth and organic compound biodegradation in engineered systems.

Microencapsulation of microbial cells

The high level of biocatalysts such as microbial cells and enzymes plays an important role in increasing the productivity of a bioreactor. The beads entrapped with microbial cells are not strong enough for long-term use. The small void space of polymer matrix and the leakage of cells limit a final cell loading in the beads. The recent success of encapsulating microbial cells makes it possible to prepare dense biocatalyst composed of recombinant microbial cells. In addition to encapsulating microbial cells, immobilization of animal and plant cells in capsules is also briefly described.

The proteolytic system of the yeast Kluyveromyces lactis

Major proteolytic activities were characterized in the yeast K. lactis NRRL 1118, grown in chemostat cultures. This yeast expressed proteolytic activities similar to those found in S. cerevisiae. This fact was particularly evident in the case of proteases such as PrA, PrB and CpY with regard to substrate specificity, activation at pH 5. 0 and inhibition patterns. The presence of a CpS activity could not be detected in either fresh or activated cell-free extracts by using the dipeptide N-Cbz-Gly-Leu, even in the presence of Zn(+2). On the other hand, K. lactis exhibits at least two major intracellular Ap activities different from those reported in other yeasts, and these seem to be carried out by closely related proteins. These activities corresponded to molecular masses of about 60 kDa, close pI values, and a similar behaviour in non-denaturing polyacrylamide electrophoresis. Both activities were enhanced by Co(+2) and inhibited by EDTA. Among different aminoacyl-p-NAs, they preferentially hydrolysed Lys-p-NA. No increase of Ap activity was obtained by incubation of extracts at acid pH. The maximum PrA and PrB activities detected in N-limited cultures were six-fold higher than those expressed under C- or P-limitation. The effect of culture conditions on the Cp and Ap expression was much less pronounced in comparison with PrA and PrB activities, Ap levels even being slightly higher in C-limited cells. This fact suggests that hydrolysis of protein to peptides might be the limiting step in the pathway of general protein degradation in the vacuole.

Process-scale disruption of microorganisms

Common hosts for the large-scale manufacture of biological products, such as Escherichia coli and Saccharomyces cerevisiae, do not excrete products to the medium. Effective techniques for cell disruption are therefore required. These include physical, chemical, enzymatic and mechanical methods. Mechanical methods such as bead milling, high-pressure homogenization, and microfluidization are preferred. However, gentler, specific methods are receiving increasing attention particularly when used in combination to synergistically exploit their different specificities. Benefits can also be derived by integrating product release and recovery. In all cases it is essential to consider the interaction of the disruption operation with downstream units and to clearly demonstrate the cost benefits of alternative strategies.