Production of aromatic alcohols and hydroxy acids by candida species and the mode of action of aromatic alcohols

Abstract

The thesis entitled “Alcohols and Hydroxy Acids by Candida Species and Their Mode of Action”, submitted by Mr. T. K. Narayanan for the Ph.D. degree of the Indian Institute of Science, Bangalore–560012, India. Yeasts, in comparison to other microorganisms, have been more intimately associated with the progress and well?being of the human race. Their contribution to human progress has been based largely on:

their capacity to bring about rapid and efficient conversion of sugars into alcohols and CO?, their varied biochemical potentialities which have been exploited in producing several fermentation products, and their role in elucidating basic biochemical and metabolic processes in living cells.

The literature pertaining to various aspects of yeasts, with special reference to the production of aromatic alcohols by yeasts and other microorganisms and their mode of action, has been presented (Chapter I). Production of p-phenylethanol (PEA) and p-indole?ethanol (IEA) by Candida albicans grown in Sabouraud’s glucose broth and their auto?antibiotic action have been reported. Investigations were carried out to examine whether this biosynthetic ability is restricted to C. albicans or shared by other Candida species as well. Five species of Candida, including both pathogenic and non?pathogenic ones, have been examined. From culture filtrates of Candida species grown in Sabouraud’s glucose broth, an oily material was obtained. Study of its physicochemical properties, UV, IR, and NMR spectral characteristics led to its identification as PEA. Its characterization was confirmed by comparison with an authentic sample. The role of the nitrogen source used in the synthetic medium on PEA production has been examined. L?Phenylalanine can replace peptone as the sole source of nitrogen. The culture filtrate was further examined for the presence of possible intermediate(s) in the biosynthesis of PEA. A simple method of extraction and purification has been described, which led to the isolation of a crystalline compound identified as p-phenyl?lactic acid (PLA). The production of PEA and PLA by Candida species has been quantified. Labelled PEA and PLA were isolated from culture filtrates of C. intermedia grown in medium supplemented with ¹?C?(U)?L?phenylalanine (Chapter II, Section A). Studies were extended to examine biosynthetic products of Candida species grown in L?tyrosine and L?tryptophan as sole nitrogen sources. Two crystalline compounds were isolated from culture filtrates of Candida species grown in medium containing L?tyrosine. They were characterized as p-(4?hydroxyphenyl)ethanol (HOPEA) and ??(4?hydroxyphenyl)lactic acid (HOPLA). Their production by Candida species has been quantified, and they were isolated in labelled form (Chapter II, Section B). Use of L?tryptophan in the medium led to the production of ??indoleethanol (IEA) and ??indolelactic acid (ILA) (Chapter II, Section C). A literature survey clearly reveals the extensive work done on the mode of action of PEA in mammalian and plant cells, bacteria, and viruses. With the exception of an isolated report that PEA and IEA inhibit the growth of C. albicans, no detailed studies have appeared so far on the mode of action of these aromatic alcohols, viz., PEA, HOPEA, and IEA in yeasts. The antibacterial and auto?antibiotic properties of these alcohols have been studied and compared. To elucidate their mode of action, their effect on:

dimorphism, growth inhibition and reversibility, respiration, uptake of labelled precursors, macromolecular synthesis, and membrane function

in C. albicans has been investigated and discussed (Chapter III).