Induction of microbial secondary metabolism

Precursors often stimulate production of secondary metabolites either by increasing the amount of a limiting precursor, by inducing a biosynthetic enzyme (synthase) or both. These are usually amino acids but other small molecules also function as inducers. The most well-known are the auto-inducers which include γ-butyrolactones (butanolides) of the actinomycetes, N-acylhomoserine lactones of Gram-negative bacteria, oligopeptides of Gram-positive bacteria, and B-factor (3’-[1-butylphosphoryl] adenosine) of Amycolatopsis mediterranei. The actinomycete butanolides exert their effects via receptor proteins which normally repress chemical and morphological differentiation (secondary metabolism and differentiation into aerial mycelia and spores respectively) but, when complexed with the butanolide, can no longer function. Homoserine lactones of Gram-negative bacteria function at high cell density and are structurally related to the butanolides. They turn on plant and animal virulence, light emission, plasmid transfer, and production of pigments, cyanide and β-lactam antibiotics. They are made by enzymes homologous to Lux1, excreted by the cell, enter other cells at high density, bind to a LuxR homologue, the complex then binding to DNA upstream of genes controlled by “quorum sensing” and turning on their expression. Quorum sensing also operates in the case of the peptide pheromones of the Gram-positive bacteria. Here, secretion is accomplished by an ATP binding casette (ABC transporter), the secreted pheromone being recognized by a sensor component of a two-component signal transduction system. The pheromone often induces its own synthesis as well as those proteins involved in protein/peptide antibiotic (including bacteriocins and lantibiotics) production, virulence and genetic competence. The B-factor of A. mediterranei is an inducer of ansamycin (rifamycin) formation

Herman Jan Phaff: professor, mentor, friend and colleague

Herman Jan Phaff, the father of yeast ecology, was born in the Netherlands in 1913. In his early years, he spent much time in his family’s winery, which sparked his interest in microbes. Trained in the famous Delft tradition, Phaff discovered many unrecognized ecological niches of yeast, such as shellfish, rabbit stomach, frass of bark beetles, tree exudates, cactus roots, Capri figs, sewage, Drosophila flies and shrimp. He is also remembered for his pioneering work on the coevolution of yeasts, insects and plants as well as for his work on yeast β-glucanase, which resulted in major advances in the understanding of the nature of the yeast cell wall. Phaff’s legacy includes research on pectin degradation by fungal enzymes and the application of molecular approaches to yeast systematics. He discovered and described many yeasts, such as the yeast named in his honor, Phaffia rhodozyma, which led to the establishment of a very important industrial fermentation process yielding high concentrations of the pigment astaxanthin, used throughout the world to provide a natural source of this important carotenoid

Genetic Regulation of fermentation organisms : fermentation, regulation, antibiotics

An effective fermentation organism is a wasteful creature that overproduces and excretes its metabolic intermediates and end products. Cultures obtained from screening programs usually possess subnormal regulatory controls. Development programs to increase product formation modify the residual control mechanisms so that the culture's "inefficiency" is increased. For production of primary metabolites, feedback inhibition and repression must be bypassed. This is usually accomplished by limiting the intracellular concentration of feedback inhibitors and repressors. Auxotrophic mutants and analogue resistant mutants are most often used for this purpose. Development of fermentations for secondary metabolites, such as antibiotics, is less rational because of our ignorance of the biosynthetic pathways and regulatory controls involved. However, evidence is accumulating that such fermentations are subject to (a) feedback regulation by the idiolite itself, (b)feedback regulation by primary metabolites that share a branched pathway with the secondary metabolite, (c) feedback regulation by inorganic phosphate, (d) catabolite regulation by rapidly utilized carbon sources, (e) induction by primary metabolites, and (f) ATP regulation. Secondary metabolites are not usually formed during growth because the enzymes of secondary metabolism are repressed during the trophophase. We have no clear idea about the type of repression control, but it probably involves growth rate as well as the factors mentioned above. Since the controls discussed above are genetically determined, mutations to increase productivity have been useful to the fermentation industry for over 30 years. Although such strain improvement programs usually involve random screening of survivors of mutagenesis, some recent progress has been made in the application of more rational screening procedures. Mutants are also used to change the spectrum of metabolites, to produce new antibiotics, and to elucidate the pathways of secondary metabolism. Extensive research is now taking place on the genetic mapping of antibiotic-producing microorganisms, especially actinomycetes. The model for this work is the genetic map of Streptomyces coelicolor, and the maps of more recently examined actinomycetes ,including Nocardia, appear to be similar. At least four of the genes of methylenomycin A production in S. coelicolorare plasmid-bound.ARNOLD L. DEMAIN, Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts

Fungal biotechnology

Fungi are used in many industrial processes, such as the production of enzymes, vitamins, polysaccharides, polyhydric alcohols, pigments, lipids, and glycolipids. Some of these products are produced commercially while others are potentially valuable in biotechnology. Fungal secondary metabolites are extremely important to our health and nutrition and have tremendous economic impact. In addition to the multiple reaction sequences of fermentations, fungi are extremely useful in carrying out biotransformation processes. These are becoming essential to the fine-chemical industry in the production of single-isomer intermediates. Recombinant DNA technology, which includes yeasts and other fungi as hosts, has markedly increased markets for microbial enzymes. Molecular manipulations have been added to mutational techniques as a means of increasing titers and yields of microbial processes and in the discovery of new drugs. Today, fungal biology is a major participant in global industry. Moreover, the best is yet to come as genomes of additional species are sequenced at some level (cDNA, complete genomes, expressed sequence tags) and gene and protein arrays become available

Comparative Genome Analysis Reveals an Absence of Leucine-Rich Repeat Pattern-Recognition Receptor Proteins in the Kingdom Fungi

Background: In plants and animals innate immunity is the first line of defence against attack by microbial pathogens. Specific molecular features of bacteria and fungi are recognised by pattern recognition receptors that have extracellular domains containing leucine rich repeats. Recognition of microbes by these receptors induces defence responses that protect hosts against potential microbial attack. Methodology/Principal Findings: A survey of genome sequences from 101 species, representing a broad cross-section of the eukaryotic phylogenetic tree, reveals an absence of leucine rich repeat-domain containing receptors in the fungal kingdom. Uniquely, however, fungi possess adenylate cyclases that contain distinct leucine rich repeat-domains, which have been demonstrated to act as an alternative means of perceiving the presence of bacteria by at least one fungal species. Interestingly, the morphologically similar osmotrophic oomycetes, which are taxonomically distant members of the stramenopiles, possess pattern recognition receptors with similar domain structures to those found in plants. Conclusions: The absence of pattern recognition receptors suggests that fungi may possess novel classes of patternrecognition receptor, such as the modified adenylate cyclase, or instead rely on secretion of anti-microbial secondary metabolites for protection from microbial attack. The absence of pattern recognition receptors in fungi, coupled with their abundance in oomycetes, suggests this may be a unique characteristic of the fungal kingdom rather than a consequence o