Metabolic effects of furaldehydes and impacts on biotechnological processes

There is a growing awareness that lignocellulose will be a major raw material for production of both fuel and chemicals in the coming decades—most likely through various fermentation routes. Considerable attention has been given to the problem of finding efficient means of separating the major constituents in lignocellulose (i.e., lignin, hemicellulose, and cellulose) and to efficiently hydrolyze the carbohydrate parts into sugars. In these processes, by-products will inevitably form to some extent, and these will have to be dealt with in the ensuing microbial processes. One group of compounds in this category is the furaldehydes. 2-Furaldehyde (furfural) and substituted 2-furaldehydes—most importantly 5-hydroxymethyl-2-furaldehyde—are the dominant inhibitory compounds found in lignocellulosic hydrolyzates. The furaldehydes are known to have biological effects and act as inhibitors in fermentation processes. The effects of these compounds will therefore have to be considered in the design of biotechnological processes using lignocellulose. In this short review, we take a look at known metabolic effects, as well as strategies to overcome problems in biotechnological applications caused by furaldehydes.     

The Corynebacterium glutamicum genome: features and impacts on biotechnological processes

Corynebacterium glutamicum has played a principal role in the progress of the amino acid fermentation industry. The complete genome sequence of the representative wild-type strain of C. glutamicum, ATCC 13032, has been determined and analyzed to improve our understanding of the molecular biology and physiology of this organism, and to advance the development of more efficient production strains. Genome annotation has helped in elucidation of the gene repertoire defining a desired pathway, which is accelerating pathway engineering. Post genome technologies such as DNA arrays and proteomics are currently undergoing rapid development in C. glutamicum. Such progress has already exposed new regulatory networks and functions that had so far been unidentified in this microbe. The next goal of these studies is to integrate the fruits of genomics into strain development technology. A novel methodology that merges genomics with classical strain improvement has been developed and applied for the reconstruction of classically derived production strains. How can traditional fermentation benefit from the C. glutamicum genomic data? The path from genomics to biotechnological processes is presented.     

New ways of selecting lactic acid bacteria for biotechnological processes

Summary Illustrated by the selection of lactic acid bacteria to be used as biological ensilage agents, new methods are introduced; they are practicable in microtitre plate dimensions by means of an automatic analysing system. According to the test setting, statements can be made on the acidifiability, the inhibition effect on contaminants and the growth under different milieu conditions. Of 126 strains tested 20 satisfied screening criteria.     

Carbamoylases: characteristics and applications in biotechnological processes

Enzymatic kinetic resolution is a widely used biotechnological tool for the production of enantiomerically pure/enriched compounds. This technique takes advantage of the enantioselectivity or enantiospecificity of an enzyme for one of the enantiomers of a racemic substrate to isolate the desired isomer. N-Carbamoyl-d- and l-amino acid amidohydrolases (d- and l-carbamoylases) are model enzymes for this procedure due to their strict enantiospecificity. Carbamoylase-based kinetic resolution of amino acids has been applied for the last three decades, allowing the production of optically pure d- or l-amino acids. Furthermore, this enzyme has become crucial in the industrially used multienzymatic system known as “Hydantoinase Process,” where the kinetic resolution produced by coupling an enantioselective hydantoinase and the enantiospecific carbamoylase is enhanced by the enzymatic/chemical dynamic kinetic resolution of the low-rate hydrolyzed substrate. This review outlines the properties of d- and l-carbamoylases, emphasizing their biochemical/structural characteristics and their biotechnological applications. It also pinpoints new applications for the exploitation of carbamoylases over the forthcoming years.     

Metabolism of fluoroorganic compounds in microorganisms: impacts for the environment and the production of fine chemicals

Incorporation of fluorine into an organic compound can favourably alter its physicochemical properties with respect to biological activity, stability and lipophilicity. Accordingly, this element is found in many pharmaceutical and industrial chemicals. Organofluorine compounds are accepted as substrates by many enzymes, and the interactions of microorganisms with these compounds are of relevance to the environment and the fine chemicals industry. On the one hand, the microbial transformation of organofluorines can lead to the generation of toxic compounds that are of environmental concern, yet similar biotransformations can yield difficult-to-synthesise products and intermediates, in particular derivatives of biologically active secondary metabolites. In this paper, we review the historical and recent developments of organofluorine biotransformation in microorganisms and highlight the possibility of using microbes as models of fluorinated drug metabolism in mammals.     

Perspectives for biotechnological production of biodiesel and impacts

In recent years, biological ways for biodiesel production have drawn an increasing attention and compared to chemical approaches, lipase-mediated alcoholysis for biodiesel production has many advantages. Currently, there are extensive reports about enzyme-mediated alcoholysis for biodiesel production, and based on the application forms of biocatalyst, the related research can be classified into immobilized lipase, whole cell catalyst, and liquid lipase-mediated alcoholysis for biodiesel production, respectively. This mini-review is focusing on the study of the aforementioned three forms of biocatalyst for biodiesel production, as well as its impacts and prospects.     

寡营养细菌及其生态作用和应用的研究进展

寡营养细菌是自然环境中特别是在寡营养环境中广泛分布的一种细菌,对寡营养生态环境起着至关重要的作用。近年来,随着分子生物学技术的飞速发展,寡营养细菌开始被广泛深入的研究。其分离培养技术,细菌形态特征,在生态中的作用和应用是目前微生物领域和环境科学领域的前沿课题,本文对这几个方面近年来的研究状况进行了综述,并展望了未来的发展趋势。     

Advantages of using thermophiles in biotechnological processes: expectations and reality

When thermophilic organisms were first considered for use in biotechnology, certain advantages were expected. The extraordinarily high reaction rates and insensitivity of processes to contaminations have not been experienced in practice, but over the last decade increasing interest has been shown in the possibility of deriving a wide variety of bioproducts from thermophiles. In addition to their high thermostability they also promise to have greater tolerance to organic solvents and a longer useful life. The possibility of recovering volatile products directly from a culture provides the opportunity to develop simplified, elegant bioprocesses. However, a series of engineering problems remain to be solved.     

Tagatose: properties, applications, and biotechnological processes

d-Tagatose has attracted a great deal of attention in recent years due to its health benefits and similar properties to sucrose. d-Tagatose can be used as a low-calorie sweetener, as an intermediate for synthesis of other optically active compounds, and as an additive in detergent, cosmetic, and pharmaceutical formulation. Biotransformation of d-tagatose has been produced using several biocatalyst sources. Among the biocatalysts, l-arabinose isomerase has been mostly applied for d-tagatose production because of the industrial feasibility for the use of d-galactose as a substrate. In this article, the characterization of many l-arabinose isomerases and their d-tagatose production is compared. Protein engineering and immobilization of the enzyme for increasing the conversion rate of d-galactose to d-tagatose are also reviewed.     

Applications of yeast flocculation in biotechnological processes

A review on the main aspects associated with yeast flocculation and its application in biotechnological processes is presented. This subject is addressed following three main aspects—the basics of yeast flocculation, the development of “new” flocculating yeast strains and bioreactor development. In what concerns the basics of yeast flocculation, the state of the art on the most relevant aspects of mechanism, physiology and genetics of yeast flocculation is reported. The construction of flocculating yeast strains includes not only the recombinant constitutive flocculent brewer's yeast, but also recombinant flocculent yeast for lactose metabolisation and ethanol production. Furthermore, recent work on the heterologous β-galactosidase production using a recombinant flocculentSaccharomyces cerevisiae is considered. As bioreactors using flocculating yeast cells have particular properties, mainly associated with a high solid phase hold-up, a section dedicated to its operation is presented. Aspects such as bioreactor productivity and culture stability as well as bioreactor hydrodynamics and mass transfer properties of flocculating cell cultures are considered. Finally, the paper concludes describing some of the applications of high cell density flocculation bioreactors and discussing potential new uses of these systems.     

Consortia of cyanobacteria/microalgae and bacteria: biotechnological potential

Microbial metabolites are of huge biotechnological potential and their production can be coupled with detoxification of environmental pollutants and wastewater treatment mediated by the versatile microorganisms. The consortia of cyanobacteria/microalgae and bacteria can be efficient in detoxification of organic and inorganic pollutants, and removal of nutrients from wastewaters, compared to the individual microorganisms. Cyanobacterial/algal photosynthesis provides oxygen, a key electron acceptor to the pollutant-degrading heterotrophic bacteria. In turn, bacteria support photoautotrophic growth of the partners by providing carbon dioxide and other stimulatory means. Competition for resources and cooperation for pollutant abatement between these two guilds of microorganisms will determine the success of consortium engineering while harnessing the biotechnological potential of the partners. Relative to the introduction of gene(s) in a single organism wherein the genes depend on the regulatory- and metabolic network for proper expression, microbial consortium engineering is easier and achievable. The currently available biotechnological tools such as metabolic profiling and functional genomics can aid in the consortium engineering. The present review examines the current status of research on the consortia, and emphasizes the construction of consortia with desired partners to serve a dual mission of pollutant removal and commercial production of microbial metabolites.     

Catabolism and biotechnological applications of cholesterol degrading bacteria

Cholesterol is a steroid commonly found in nature with a great relevance in biology, medicine and chemistry, playing an essential role as a structural component of animal cell membranes. The ubiquity of cholesterol in the environment has made it a reference biomarker for environmental pollution analysis and a common carbon source for different microorganisms, some of them being important pathogens such as Mycobacterium tuberculosis. This work revises the accumulated biochemical and genetic knowledge on the bacterial pathways that degrade or transform this molecule, given that the characterization of cholesterol metabolism would contribute not only to understand its role in tuberculosis but also to develop new biotechnological processes that use this and other related molecules as starting or target materials.     

Biology of Pleurotus eryngii and role in biotechnological processes: a review

Pleurotus eryngii is considered a complex species owing to a perplexed structure within species and a wide geographical distribution. Due to its remarkable flavor, high nutritional value, and numerous medicinal features, P. eryngii is commercially cultivated on various raw plant materials. Its efficacy in using nutrients from lignocellulose residues is based on possession of a potent ligninolytic enzyme system, constituted of laccase, Mn-oxidizing peroxidases, and aryl-alcohol oxidase, which successfully degrade different aromatic compounds. Similarly, due to the ability of these enzymes, P. eryngii plays a very important role in many biotechnological processes, such as food production (edible basidiomata), biotransformation of raw plant materials to feed, biopulping and biobleaching of paper pulp, as well as bioremediation of soil and industrial waters.     

Microbial iron respiration: impacts on corrosion processes

In this review, we focus on how biofilms comprising iron-respiring bacteria influence steel corrosion. Specifically, we discuss how biofilm growth can affect the chemistry of the environment around the steel at different stages of biofilm development, under static or dynamic fluid regimes. We suggest that a mechanistic understanding of the role of biofilm metabolic activity may facilitate corrosion control.     

Quinoproteins: structure, function, and biotechnological applications

A new class of oxidoreductase containing an amino acid-derived o-quinone cofactor, of which the most typical is pyrroloquinoline quinone (PQQ), is called quinoproteins, and has been recognized as the third redox enzyme following pyridine nucleotide- and flavin-dependent dehydrogenases. Some quinoproteins include a heme c moiety in addition to the quinone cofactor in the molecule and are called quinohemoproteins. PQQ-containing quinoproteins and quinohemoproteins have a common structural basis, in which PQQ is deeply embedded in the center of the unique superbarrel structure. Increased evidence for the structure and function of quinoproteins has revealed their unique position within the redox enzymes with respect to catalytic and electron transfer properties, and also to physiological and energetic function. The peculiarities of the quinoproteins, together with their unique substrate specificity, have encouraged their biotechnological application in the fields of biosensing and bioconversion of useful compounds, and also to environmental treatment.     

Effect of impurities in biodiesel-derived waste glycerol on the performance and feasibility of biotechnological processes

The rapid development of biodiesel production technology has led to the generation of tremendous quantities of glycerol wastes, as the main by-product of the process. Stoichiometrically, it has been calculated that for every 100 kg of biodiesel, 10 kg of glycerol are produced. Based on the technology imposed by various biodiesel plants, glycerol wastes may contain numerous kinds of impurities such as methanol, salts, soaps, heavy metals, and residual fatty acids. This fact often renders biodiesel-derived glycerol unprofitable for further purification. Therefore, the utilization of crude glycerol though biotechnological means represents a promising alternative for the effective management of this industrial waste. This review summarizes the effect of various impurities-contaminants that are found in biodiesel-derived crude glycerol upon its conversion by microbial strains in biotechnological processes. Insights are given concerning the technologies that are currently applied in biodiesel production, with emphasis to the impurities that are added in the composition of crude glycerol, through each step of the production process. Moreover, extensive discussion is made in relation with the impact of the nature of impurities upon the performances of prokaryotic and eukaryotic microorganisms, during crude glycerol bioconversions into a variety of high added-value metabolic products. Finally, aspects concerning ways of crude glycerol treatment for the removal of inhibitory contaminants as reported in the literature are given and comprehensively discussed.