Studies on the metabolism of the mould aspergillus falvus

Abstract

Synopsis of the thesis entitled “Studies on the Metabolism of the Mould Aspergillus flavus” submitted to the University of Bombay for the Degree of Doctor of Philosophy. In recent years, the study of mould metabolism has gained considerable importance in the field of microbiology. The complex reactions taking place in the living cell present innumerable problems to the biochemist. The conditions under which these reactions occur, and the maintenance of normal equilibrium, are highly fascinating. The formation of numerous metabolites during the growth of an organism, and its adaptation to various environmental conditions, have attracted increasing attention. Modern biochemical methods used for the resolution of enzyme systems have contributed valuable information on the formation of cellular material as well as the nature and fate of catabolic products. Moulds occupy a unique position in such investigations because:

they can be conveniently cultivated under controlled conditions, they respond sensitively to even minute environmental changes, and they exhibit rapid growth.

Thus, the pathways involved in the formation of metabolites, utilisation of growth substrates, and fate of metabolic products provide a fruitful line of study. A systematic investigation of mould metabolic processes contributes significantly to the understanding of complex biological reactions in higher plants and animals. The present work involves a study of the various metabolic processes in the mould Aspergillus flavus, focusing on the mechanism of formation and nature of its metabolites. The thesis consists of six chapters:

Chapter I A short historical introduction and the present state of knowledge on mould metabolism are given. The significance of the present investigation and the approach adopted are briefly discussed.

Chapter II This chapter describes the isolation of the mould, its cultural characteristics, growth behaviour, and methods of maintenance.

Chapter III - Carbohydrate Metabolism The various aspects of carbohydrate metabolism in A. flavus are discussed. Key studies include:

The effect of different sugars on growth. Changes in the composition of the culture medium, followed by circular paper chromatography. Formation of several oligosaccharides during growth. Enzymes in the mycelium capable of synthesising oligosaccharides from sucrose, lactose, cellobiose, and maltose.

Several trisaccharides formed from sucrose, lactose, and cellobiose were isolated using cellulose and charcoal-celite columns. Their physical and chemical properties were determined. Quantitative studies include the influence of:

hydrogen ion concentration (pH), metallic ions, enzyme concentration, substrate concentration

on enzyme activity. Factors influencing amylase activity in A. flavus were also investigated.

Chapter IV - Thiamine Synthesis Studies on the synthesis of thiamine by A. flavus are presented. Investigated factors include:

Optimal conditions for thiamine formation, Use of indigenous materials such as oil cakes (groundnut, sesame), wheat bran, and germinated seed extracts.

Groundnut cake supported the best growth and the highest thiamine synthesis. Other parameters examined:

pH: optimum found to be 6.6, Temperature: optimum at l°C (as reported in the original text), Influence of nitrogen salts: most showed similar potency at 0.4%, with higher concentrations reducing thiamine content in both mycelium and culture medium.

Chapter V - Phosphatases and Proteolytic Enzymes This chapter discusses:

Identification of two acid and two alkaline phosphomonoesterases, Presence of an inorganic pyrophosphatase, Optimum pH values for these enzyme systems, Enzyme activity over different stages of growth.

Kinetic studies include:

effect of substrate concentration, effect of enzyme concentration, effect of time.

Effects of metal ions:

Beryllium: inhibitory to both alkaline phosphatases, Magnesium: strongly activates one alkaline phosphatase (pH 8.75), Cyanide: inhibits the phosphatase of pH 8.75 but not the other.

Amino acid composition of mycelium and culture medium during growth was followed quantitatively via circular paper chromatography.

Chapter VI This chapter presents the significance of amino acid changes in relation to nitrogen metabolism, based on day to day compositional analysis during mould growth.