The Kinetics of Metabolism of Gibberella Fujikuroi in Stirred Culture

Abstract

Some aspects are described of tlie kinetics of the groivth of (;ibbeie!la fzljik~~ro?:in nitrogen-limited media contai~ling either am~uonium nitrate, ammonium acetate, ammonium tartl-ate, urea, or glycine. Also varied were inoculum size, agitation rate, pI-I, and initial concentrations of glucosc and nitrogen source. The sigiiihcance of kinetic parameters ~lsed in this, and published studies, is discussed.A lag phase n:as only found on ammonium acetate media or when higli concentrations of glucose \\,ere present. Early gro\vth was exponei~tial on all nitrogen sources. On ammonium acetate the specilic growth rate decreased a t a dry weight ofca. 1 mg/g WS (Whole ~~nliltered Samplc). On arnmol~iuin nitrate, early expoiientiaI growth ~~t i l i z e d more NI-13-nitrogen than NOJ-l~itrogen \vith a corlcornitant decrease in pH. I n the range pH 3.0-2.8 NHa-nitrogen uptalre and dry weight increase ceased, but SOs-nitrogen uptalce continued, and the pH increased until growth and NI-I:,-nitrogen uptalce restarted. 'This pattern could be repeated. Finally, expo~lential growth was resumed a t a lo\\, specilic gro\\.th rate. On gIycine, urea, and ammoni~lm tartrate media, exponel~tial growth continned to a dry weight of about 7 mg/g \VS. During, this pcriod the uptalces relative to dry weight (contributions) of glucose, nttrogen, phosphate, and magnesium remained coilstant and were unaffected by the rate of agltatloll, as also was the specihc growth rate, but the latter decreased with increasing glucose concentration.A period of linear growth could folio\\, the exponential period. The contribution bf glucose was ireater, and that of phosphate and magnesium less, than during exponential growth. The dry weight a t which espol~ential growth changed to linear growth \\.as greater the higher the rate of agitation, and this change may be a response to oxygen restriction. After nitrogen exhaustion, fat and carbohydrate accum~llntion in tlie cells largely accour~ted for the increase in dry weight. The specilic rates of dry weight increase and glucose uptake remained constant over the lower range of initial nitrogen concentrations. Both rates decreased with increasing nitrogen over the higher range.Gibberellic acid production began a t , or soon after, nitrogen exhaustion. The amount present increased lirlearly with time. The productivity decreased with increasing glucose conce~~tration; and first increased and then decreased with increasing initial nitrogen. 'I'he maximum amount produced was proportional to the initial nitrogen provided. Some published results are discussed in the light of these relations.

A Kinetic Study of the Growth of Aspergillus nidulans and Other Fungi

“…The specific growth rate (a) is a direct measure of the growth rate of an organism and may be calculated from the expression : a = In 2 / t d , where t d is the doubling or mean effective generation time. Several workers have shown that filamentous fungi grow exponentially in submerged culture (Zalokar, 1959a;Pirt & Callow, 1960;Borrow et al 1964). Swanson & Stock (1966), however, reported that the growth of Microsporum quinckeanum in submerged culture was not logarithmic.…”

Regulation of Gibberellin Biosynthesis in Gibberella fujikuroi

“…Gibberellin production by Gibberella depends upon the nature of the carbon and nitrogen sources and is stimulated by a high carbon to nitrogen ratio (2,11,13). Gibberellin production follows cessation of growth and exhaustion of the nitrogen source in batch cultures (2) and does not occur at low growth rates and low nitrogen concentrations (less than 65 mg L`' in the form of glycine) in a chemostat (6).…”

Gibberellin biosynthesis inGibberella

“…Gibberellin biosynthesis slows down at high glucose concentrations (Borrow et a/., 1964;Candau eta/., 1992). As a consequence, gibberellin production improves if the glucose concentration is kept low.…”