Actinobacteria are Gram-positive bacteria with high G+C DNA content that constitute one of the largest bacterial phyla, and they are ubiquitously distributed in both aquatic and terrestrial ecosystems. Many Actinobacteria have a mycelial lifestyle and undergo complex morphological differentiation. They also have an extensive secondary metabolism and produce about two-thirds of all naturally derived antibiotics in current clinical use, as well as many anticancer, anthelmintic, and antifungal compounds. Consequently, these bacteria are of major importance for biotechnology, medicine, and agriculture. Actinobacteria play diverse roles in their associations with various higher organisms, since their members have adopted different lifestyles, and the phylum includes pathogens (notably, species of Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, and Tropheryma), soil inhabitants (e.g., Micromonospora and Streptomyces species), plant commensals (e.g., Frankia spp.), and gastrointestinal commensals (Bifidobacterium spp.). Actinobacteria also play an important role as symbionts and as pathogens in plant-associated microbial communities. This review presents an update on the biology of this important bacterial phylum.

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Taxonomy, Physiology, and Natural Products of Actinobacteria

To succeed, many cells must alternate between life-styles that permit rapid growth in the presence of abundant nutrients and ones that enhance survival in the absence of those nutrients. One such change in life-style, the “acetate switch,” occurs as cells deplete their environment of acetate-producing carbon sources and begin to rely on their ability to scavenge for acetate. This review explains why, when, and how cells excrete or dissimilate acetate. The central components of the “switch” (phosphotransacetylase [PTA], acetate kinase [ACK], and AMP-forming acetyl coenzyme A synthetase [AMP-ACS]) and the behavior of cells that lack these components are introduced. Acetyl phosphate (acetyl∼P), the high-energy intermediate of acetate dissimilation, is discussed, and conditions that influence its intracellular concentration are described. Evidence is provided that acetyl∼P influences cellular processes from organelle biogenesis to cell cycle regulation and from biofilm development to pathogenesis. The merits of each mechanism proposed to explain the interaction of acetyl∼P with two-component signal transduction pathways are addressed. A short list of enzymes that generate acetyl∼P by PTA-ACKA-independent mechanisms is introduced and discussed briefly. Attention is then directed to the mechanisms used by cells to “flip the switch,” the induction and activation of the acetate-scavenging AMP-ACS. First, evidence is presented that nucleoid proteins orchestrate a progression of distinct nucleoprotein complexes to ensure proper transcription of its gene. Next, the way in which cells regulate AMP-ACS activity through reversible acetylation is described. Finally, the “acetate switch” as it exists in selected eubacteria, archaea, and eukaryotes, including humans, is described.

The acetate switch.

Based on the principles and metrics of green chemistry and sustainable development, biocatalysis is both a green and sustainable technology. This is largely a result of the spectacular advances in molecular biology and biotechnology achieved in the past two decades. Protein engineering has enabled the optimization of existing enzymes and the invention of entirely new biocatalytic reactions that were previously unknown in Nature. It is now eminently feasible to develop enzymatic transformations to fit predefined parameters, resulting in processes that are truly sustainable by design. This approach has successfully been applied, for example, in the industrial synthesis of active pharmaceutical ingredients. In addition to the use of protein engineering, other aspects of biocatalysis engineering, such as substrate, medium, and reactor engineering, can be utilized to improve the efficiency and cost-effectiveness and, hence, the sustainability of biocatalytic reactions. Furthermore, immobilization of an enzyme ...

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Role of Biocatalysis in Sustainable Chemistry

Summary: Actinobacteria constitute one of the largest phyla among Bacteria and represent gram-positive bacteria with a high G+C content in their DNA. This bacterial group includes microorganisms exhibiting a wide spectrum of morphologies, from coccoid to fragmenting hyphal forms, as well as possessing highly variable physiological and metabolic properties. Furthermore, Actinobacteria members have adopted different lifestyles, and can be pathogens (e.g., Corynebacterium, Mycobacterium, Nocardia, Tropheryma, and Propionibacterium), soil inhabitants (Streptomyces), plant commensals (Leifsonia), or gastrointestinal commensals (Bifidobacterium). The divergence of Actinobacteria from other bacteria is ancient, making it impossible to identify the phylogenetically closest bacterial group to Actinobacteria. Genome sequence analysis has revolutionized every aspect of bacterial biology by enhancing the understanding of the genetics, physiology, and evolutionary development of bacteria. Various actinobacterial genomes have been sequenced, revealing a wide genomic heterogeneity probably as a reflection of their biodiversity. This review provides an account of the recent explosion of actinobacterial genomics data and an attempt to place this in a biological and evolutionary context.

Genomics of Actinobacteria: Tracing the Evolutionary History of an Ancient Phylum

The complete Corynebacterium glutamicum ATCC 13032 genome sequence and its impact on the production of l-aspartate-derived amino acids and vitamins

For almost 50 years now, biotechnological production processes have been used for industrial production of amino acids. Market development has been particularly dynamic for the flavor-enhancer glutamate and the animal feed amino acids L: -lysine, L: -threonine, and L: -tryptophan, which are produced by fermentation processes using high-performance strains of Corynebacterium glutamicum and Escherichia coli from sugar sources such as molasses, sucrose, or glucose. But the market for amino acids in synthesis is also becoming increasingly important, with annual growth rates of 5-7%. The use of enzymes and whole cell biocatalysts has proven particularly valuable in production of both proteinogenic and nonproteinogenic L: -amino acids, D: -amino acids, and enantiomerically pure amino acid derivatives, which are of great interest as building blocks for active ingredients that are applied as pharmaceuticals, cosmetics, and agricultural products. Nutrition and health will continue to be the driving forces for exploiting the potential of microorganisms, and possibly also of suitable plants, to arrive at even more efficient processes for amino acid production.

Biotechnological production of amino acids and derivatives: current status and prospects

Amino Acids – Technical Production and Use

2.1. Fermentative preparation of amino acids for animal feed supplement purposes is a complex process, since the amino acid is present in the fermentation broth at only a few percent. Drying the crude fermentation broth and using it as such generally led to aggregating sticky products or to products having too low a supplementary amino acid content. Using the new animal feed supplement and preparation process, a supplementary amino acid is intended to be made available which is not too expensive, not excessively hygroscopic or sticky, and whose contents can be standardised. 2.2. The animal feed supplement is based on a fermentation broth and contains the majority of its components, if required, with the exception of part of the biomass. Preferably, the biomass is present at no more than 10 % by weight of the dry matter. Proteins are preferably present at up to a maximum of 10 % by weight. For the production, during fermentation, at least towards the end, the sugar content is adjusted to a value of at most 4 g/l and during further processing, if required, at least a part of the biomass is separated off. 2.3. Supplementation or preparation of animal feed agents or premixes, in particular containing lysine.

Animal feed supplement based on fermentation broth-amino acid, process for its production and its use

The review covers the development of membrane reactor technologies at Degussa for the synthesis of fine chemicals. The operation of fed-batch or continuous biocatalytic processes in the enzyme membrane reactor (EMR) is well established at Degussa. Degussa has experience of running EMRs from laboratory gram scale up to a production scale of several hundreds of tons per year. The transfer of the enzyme membrane reactor from biocatalysis to chemical catalysis in the chemzyme membrane reactor (CMR) is discussed. Various homogeneous catalysts have been investigated in the CMR, and the scope and limitation of this new technique is discussed.

Membrane reactors at Degussa.

For the industrial production of L-amino acids, each of these processes has its importance. TABLE 1 shows an overview of the processes that are practiced for the production of individual amino acids, which are used as flavoring agents, feed additives, and in infusion solutions. Enzymatic catalysis is advantageous for cases where L-amino acids can be produced with high specificity from inexpensive precursors in a continuously operating process. The acylase-catalyzed stereospecific hydrolysis of N-acetyl-DL-amino acids is employed industrially for the production of L-alanine, L-valine, L-methionine, Lphenylalanine, and L-tryptophan. Enzymatic resolution can only be competitive when coupled with an efficient enzyme recycling or immobilization system and an easy racemization of the undesired acetyl-D-amino acids (FIG. I ) . enantiomeric compounds used as fine chemicals or pharmaceuticals:

Wolfgang Leuchtenberger

Papers

Biotechnological production of amino acids and derivatives: current status and prospects

Amino Acids – Technical Production and Use

Animal feed supplement based on fermentation broth-amino acid, process for its production and its use

Membrane reactors at Degussa.

Scale-up of an Enzyme Membrane Reactor Process for the Manufacture of l-Enantiomeric Compounds