Showing papers in "Advances in Microbial Physiology in 1969"

Biosynthesis of Secondary Metabolites: Roles of Trace Metals

Abstract: Publisher Summary This chapter discusses the characteristics and functions of secondary metabolites and explains the inclusion of an additional class of substances in this category It suggests reasons for the need of secondary metabolism for unique quantities of trace metals Secondary metabolites are defined as natural products that have a restricted taxonomic distribution, possess no obvious function in cell growth, and are synthesized by cells that have stopped dividing Information gained from examination of both secondary metabolites that have medicinal or poisonous effects as well as those that are pharmacologically inactive has contributed to our understanding of the chemosynthetic functions of non-proliferating microbial cells The functions applicable to all secondary metabolites include (1) waste products of cellular metabolism, (2) reserve food-storage materials, (3) breakdown products derived from cellular macromolecules, and (4) “safety-valve” shunts of very low molecular-weight precursors into innocuous products Secondary metabolites are considered to be low molecular weight materials with an upper limit of about 1500 Many attempts have been made to obtain formation of secondary metabolites in cell-free systems A number of these attempts have been unsuccessful because (1) extracts were prepared at incorrect times during the growth cycle, (2) an incorrect mixture of soluble- and membrane fractions were employed, or (3) a number of sequentially active enzymes are needed but not all of these were present in the cells at the time of fractionation

Antimicrobial Agents and Membrane Function

Abstract: Publisher Summary This chapter explains the interactions of antibiotics (and antimicrobial agents generally) with cellular membranes, and the application of these reagents to the study of membrane physiology in micro-organisms. Much of the experimental material currently available refers to mitochondria and to artificial membrane systems, perhaps because biochemists were alert to the selective effects of many antibiotics on membrane functions. The chapter is restricted to those functions, which appear to be intrinsically associated with membranes: impermeability to small molecules, active transport, and the generation of metabolic energy. Eucaryotic cells, such as fungi and algae, differ fundamentally from the procaryotic bacteria in the organization of membranous elements. In the former, the plasma membrane serves as the main osmotic barrier and energy generation is the function of specialized organelles, mitochondria, and chloroplasts. In procaryotic cells, the division of labor is much less obvious. Exposure of bacteria to certain compounds—including organic solvents and detergents, destroys the osmotic barrier. This is readily recognized by release from the cells of small metabolites such as K+, phosphate, amino acids and sugars, and is generally lethal. The concept that ions traverse membranes in association with lipid-soluble carriers is traditional in membrane physiology, but it been recognized recently that certain pharmacological agents exert their effects by serving as artificial ion carriers.

Catabolite Repression and other Control Mechanisms in Carbohydrate Utilization

Abstract: Publisher Summary This chapter focuses on three devices: catabolite repression, transient repression, and catabolite inhibition, which regulate the utilization of many carbohydrates. Catabolite repression is a reduction in the rate of synthesis of certain enzymes, particularly those of degradative metabolism, in the presence of glucose or other readily metabolized carbon sources. Catabolite inhibition is a control exerted by glucose on enzyme activity rather than on enzyme formation, analogous to feedback inhibition in biosynthetic pathways. Catabolite repression influences many aspects of microbial growth and metabolism. In addition to the well known repressions of carbohydrate utilization and amino-acid degradation in bacteria and yeast, catabolite repression affects the formation of enzymes that function in the tricarboxylic acid cycle, glyoxylate cycle, fatty acid degradation, carbon dioxide fixation, and the respiratory chain. In higher organisms, catabolite repression has been observed in sugar cane, rats, and man. The question of whether catabolite repression acts to inhibit the transcription of DNA into m-RNA or to inhibit translation of messenger into protein has received conflicting answers. Catabolite repression is a control system that usually affects catabolic enzymes. If catabolite repression and transient repression are not mediated by the specific apo-repressor of each operon, there must be another protein that recognizes the low molecular-weight effector. The significance of a control mechanism, which influences the activity as opposed to the concentration of a carbohydrate-metabolizing enzyme is readily appreciated because bacteria have a limited ability to change enzyme concentrations.

The Roles of Exogenous Organic Matter in the Physiology of Chemolithotrophic Bacteria

Abstract: Publisher Summary Chemolithotrophy is defined as the production of metabolically useful energy by the oxidation of inorganic compounds. Chemolithotrophy is coupled to a specific assimilatory physiology, the utilization of carbonic acid as the exclusive carbon source, as well as to exogenous organic matter. Attempts have been made to unify into a single concept, the aspects of physiology, energy generation, and carbon assimilation that are independent, in all possible combinations. This chapter deals with the roles of exogenous organic compounds in the physiology of chemolithotrophic bacteria. The chapter considers autotrophy and mixotrophy, the former refers to a completely inorganic medium or cells grown in such a medium and latter to a commingling of alternative modes of energy generation or carbon assimilation. Facultative autotrophs that oxidize either molecular hydrogen or reduced inorganic sulfur compound and obligate autotrophs in which energy is derived chemolithotrophically by the oxidation of ammonia or nitrite, reduced inorganic sulfur compounds, or ferrous ion are also presented.

The Place of Continuous Culture in Microbiological Research

Abstract: Publisher Summary This chapter focuses on the importance of continuous culture in microbiological research. The present theory of continuous culture and its practicability stem from this dependence of growth rate on nutrient concentration. It is appropriate, therefore, to consider the behavior of organisms growing in a “continuous” culture. Although occasional attempts have been made to equate organisms growing in a continuous culture with similar organisms in a batch culture at specific stages of the growth cycle, basically the two situations are entirely different. With a complex medium, such as a tryptic digest of meat or acid hydrolysed casein, it would be difficult to ascertain the nature of the environmental change that would limit growth, this probably would vary with parameters such as temperature and medium-flow rate. To exploit continuous-culture methods to the full, it is essential to understand not only the ways in which this technique can succeed but also the ways in which it may possibly fail. The single advantage to be gained from growing cultures in a chemostat is that the environment is controlled and invariant with time; thus phenotypic variations in the population are minimized. There is an urgent need for the manufacture and marketing of a simple (and cheap) chemostat that is suitable for teaching purposes. Only then can students acquire early experience in the practice of continuous culture and overcome the doubts and inhibitions generated by exposure to the theoretical complexities of the system.

Thermophilic Bacteria and Bacteriophages

Abstract: Publisher Summary This chapter emphasizes on thermophilic bacteria belonging to the genus Bacillus and to the bacteriophages, which attack these organisms. The chapter considers three main groups of bacteria that include (1) strict or obligate thermophiles, these organisms show optimal growth at 65°–70°, and do not grow below 40°–42°; (2) facultative thermophiles, which have a maximum temperature for growth between 50° and 65°, and are capable of growth at room temperature; and (3) thermotolerant organisms, which have a maximum growth temperature of 45°–50° and also grow at room temperature. Thermophiles are isolated from soils of both temperate and tropical regions, air, salt, fresh water, from foods and grain, raw, pasteurized milk, and in faeces of man and domestic animals. As the incubation temperature for a thermophile is increased, there is an increase in the growth requirements of the particular organism under study. A thermophilic phage isolated from sewage-polluted river water exhibited an optimum temperature for lytic activity of about 50°, and had the ability to lyse its host at 57°–58°. The thermostability of the phage largely depends on the suspending fluid. In phosphate buffer or distilled water, the heat resistance is found to be less than when the phage is in broth or gelatin solution.

The Aliphatic Amidases of Pseudomonas aeruginosa

Abstract: Publisher Summary This chapter focuses on the aliphatic amidases of Pseudomonas aeruginosa. Several different classes of enzymes are known to hydrolyse some amide bonds. Many proteolytic enzymes can hydrolyse peptide or amino-acid amides, e.g., trypsin and papain hydrolyse benzoyl argininamide and leucine aminopeptidase hydrolyses leucinamide, aminobutyramide, and glycinamide. The chapter is concerned with the amidase produced by P. aeruginosa 8602. This is a typical strain but does not produce pyocyanin or a haemolysin. It grows well in a minimal salts medium at 30° or 37° and can utilize a wide range of carbon compounds as growth substrates. Acetamide and propionamide are good substrates and inducers and can provide both carbon and nitrogen for growth. Other amides, such as glycollamide and acrylamide, are also good substrates but the substrate specificity differs from the inducer specificity, e.g., lactamide is a very poor substrate but has the same inducing capacity as propionamide. Mutants of Pseudomonas aeruginosa 8602 producing amidase in the absence of inducer (C mutants) were first isolated on S/F agar plates. The genetic study of pseudomonads is much less developed than that of Escherichia coli or Salmonellu typhimuriurn but transfer of genetic material by conjugation has been known for some years. The nutritional versatility of pseudomonads offers many possible biochemical variations of metabolic pathways and regulatory mechanisms. The properties of the various regulator mutants have suggested that the regulation of amidase synthesis is controlled by a regulator gene of the lac i-type, producing a cytoplasmic repressor that in the wild type prevents amidase synthesis unless an inducer is present.

Assimilatory and Dissimilatory Metabolism of Inorganic Sulphur Compounds by Micro-Organisms

Abstract: Publisher Summary Sulfur is an essential element for the growth and activity of all living cells. Sulfur metabolism involves both reductive and oxidative processes and the co-operative action of these processes gives rise to the sulfur cycle in which sulfur is continually recycled between sulfate and reduced forms such as sulfide and sulfur-amino acids. The cycle embraces an eight-electron change between sulfate and sulfide and can involve the formation of intermediates, which have no stable counterparts in chemistry. The two classes of biological sulfate reduction includes—namely,(1) assimilatory, small-scale reductions of sulfate to sulfur-containing amino acids and (2) dissimilatory, large-scale transformations of sulfate to sulfide, which are linked to energy-yielding reactions in the organism. This chapter describes assimilatory and dissimilatory terms to distinguish transformations of inorganic sulfur compounds, which lead to the formation of cell constituents from those oxidative and reductive processes that are concerned primarily with energy metabolism. Essentially, assimilatory sulfate-reducing microorganisms depend on 3′-Phosphoadenylylsulfate (PAPS) reductase for cysteine biosynthesis and dissimilatory sulfur metabolism—both reductive and oxidative— are linked to Adenylylsulfate (APS) reductase.

The F-Pilus of Escherichia coli

Abstract: Publisher Summary This chapter deals with F-pilus—sex hair, sex pilus, F-fimbria, and sex firnbria— of Escherichia coli . It essentially describes methods of assay and synthesis of F-pili, their functions and properties, and the mutant approach to the F-pilus problem. F-pili first observed, differed from common pili by the random adsorption of small RNA viruses along their sides. F-pili are both longer and wider than Type I or common pili. Frequent appearance of knobs or enlargements at their distal extremities is also used to distinguish F-pili in micrographs. Free F-pili from the supernatant of a culture of male cells can be treated with ultrasonic vibrations to yield smaller fragments, which are capable of adsorbing phage, largely confirm that the filaments are made of number of repeating structural units, each of which can bind the RNA phage. Knowledge of the structure of F-pili can essentially shed light on various functions, which these filaments perform in phage injection and mating. F-pili also play an important role in the mating process of E .coli and also serve the function of adsorption organelles for male phages.

Serotype Expression in Paramecium

Abstract: Publisher Summary This chapter discusses the ciliated protozoan Paramecium aurelia , mainly the differentiation of its serotypes or surface immobilization antigens (i-antigens). This system has several features advantageous in the study of gene expression. For example, paramecia exhibit a range of readily distinguishable, alternative cell-types, expressing a character that is essential for the existence of the cell but is nevertheless neutral in the selective sense. These serotypes are generally mutually exclusive and can often be made to change reversibly, one to another, in response to standard changes in their environment. Paramecium aurelia is routinely considered as a large micro-organism or a small animal and even has features normally associated with plants. Paramecium possesses two types of nuclei, which are morphologically and functionally distinct. The micronuclei (usually two), which closely resemble the nuclei of eucaryotic cells, are the germinal nuclei. The single macronucleus is very large and is the physiologically active component, controlling the phenotypic features of the cell.

Encystment in Amoebae

Abstract: Publisher Summary This chapter focuses on encystment of amoebae. Many of the eucaryotic protista appear to be capable of encystment. In some cases, the formation of a cyst is related to the processes of sexual or asexual reproduction, but it is generally considered to be a response to environmental conditions that are suboptimum for growth of the organism. Encystment usually involves a drastic reorganization of the subcellular structure of the vegetative cell in which cilia, flagella, vacuoles, and other inclusions disappear. Much of our knowledge of encystment is based on data, which are included in reports of a general nature. Encystment can also be considered as an example of cellular differentiation. Many of the earlier investigations of encystment were carried out in mixed cultures, which ranged from the completely agnotobiotic to monoxenic cultures in which the protozoan was grown with a known microbial associate, usually a bacterium. The first ten hours of encystment in non-nutrient replacement media is marked, in H . castellanii, by an increase in the rate of oxygen uptake of the amoebae. After this initial increase, the rate of oxygen consumption decreases gradually to an immeasurable value by the time cyst formation is complete. The amoebae also show changes in the utilization of exogenous substrates during the first ten hours of encystment.

The Physiology of Ectotrophic Mycorrhizas

Abstract: Publisher Summary Mycorrhiza refers to a wide variety of associations between fungi and other plants. Frank referred to mycorrhiza as the dual system present in the ultimate rootlets of members of the Cupuliferae and Pinaceae. Essentially, in these species, the mycorrhizal condition is ectotrophic—in which the fungal partner forms an enveloping sheath around the ultimate rootlets of the host, together with intercellular hyphae of limited extent, commonly referred as the “Hartig Net.” This chapter deals with the physiology of ectotrophic mycorrhizas, especially those of the European beech, Fagus sylvatica, and various pines, Pinus spp. The physiology of mycorrhiza demonstrates two levels of interaction between the associated fungi and hosts—namely, there is interaction at a hormonal or micronutrient level, which is essential to the erection of the symbiotic union and once the symbiotic dual organism is established; the second interaction at a macronutrient level develops fully. Organic nutrients as carbohydrates also pass to the fungus through the body of which mineral nutrients absorbed from the soil pass to the host. These transfers are largely metabolically dependent.

Oxygen Metabolism by Micro-organisms

Abstract: Publisher Summary Biological oxidation is often brought about directly by the addition of molecular oxygen. In quantitative terms, especially in microbes, the most important role of oxygen is of terminal electron acceptor. This chapter discusses electron-transport systems, involving oxygen and oxygenase systems particularly in microbial systems. It describes the problems associated with these transport systems. The chapter concludes with description of major advances in instrumentation, which have made possible more precise study of the influence of oxygen on growth and metabolism. Aerobic and the anaerobic systems, both in prokaryote membrane systems and eukaryote organelles, are largely controlled by oxygen tension. The effects of oxygen extend not only to the enzymes that utilize oxygen, such as the succinate oxidase system, but also to associated enzyme systems involved in glycolysis and the TCA cycle. The magnitude of the uptake and binding of molecular oxygen by micro-organisms indicates the scale of the utilization of substrates whose assimilation is absolutely dependent on oxygenases, often in the initial stages of catabolism. Competition between oxygen-utilizing biosynthetic pathways and oxygen as a terminal electron acceptor is unlikely at high oxygen tensions but can occur in low oxygen tensions, when substrates depending on oxygenases are involved.