Growth of Aspergillus nidulans in a thin liquid layer

Effect of different carbon sources on morphology and silver accumulation in Cochliobolus lunatus

The morphology of filamentous fungi plays very important role in uptake of metabolites and enzyme production. A filamentous fungus may be fibrous, hyphae, pellets, clumps, etc. Cochliobolus lunatus is a fungus which has previously been reported for silver accumulation and nanoparticles formation. The present study investigated the role of various carbon sources on morphology, biochemical profile, silver accumulation, and biosynthesis of silver nanoparticles by fungal strain C. lunatus. In this investigation, effect of different carbon sources was studied on morphology of C. lunatus and its silver accumulating ability. As a result of different carbon sources like carboxymethyl cellulose (CMC), pectin, starch, agar, sucrose, and mannitol, the organism showed three kinds of morphologies like homogenous smooth branched clumps, tough short fibrous filaments, and tough pellets, as well as silver accumulating ability. Atomic absorption spectroscopy (AAS) studies showed maximum uptake of Ag(+): 87.44 ± 0.23 and 82.57 ± 0.19 % in pectin- and CMC-grown biomass, respectively. The crystalline nature of silver nanoparticles (AgNPs) was confirmed by X-ray diffraction studies. Transmission electron microscopy (TEM) micrographs of silver nanoparticles confirmed size ranging from 5 to 38 nm.

Effect of branch frequency in Aspergillus oryzae on protein secretion and culture viscosity

Highly branched mutants of two strains of Aspergillus oryzae (IFO4177, which produces alpha-amylase, and a transformant of IFO4177 [AMG#13], which produces heterologous glucoamylase in addition to alpha-amylase) were generated by UV or nitrous acid mutagenesis. Four mutants of the parental strain (IFO4177), which were 10 to 50% more branched than the parental strain, were studied in stirred batch culture and no differences were observed in either the amount or the rate of enzyme production. Five mutants of the transformed parental strain (AMG#13), which were 20 to 58% more branched than the parental strain, were studied in either batch, fed-batch or continuous culture. In batch culture, three of the mutants produced more glucoamylase than the transformed parental strain, although only two mutants produced more glucoamylase and alpha-amylase combined. No increase in enzyme production was observed in either chemostat or fed-batch culture. Cultures of highly branched mutants were less viscous than those of the parental and transformed parental strains. A linear relationship was found between the degree of branching (measured as hyphal growth unit length) and culture viscosity (measured as the torque exerted on the rheometer impeller) for these strains. DOT-controlled fed-batch cultures (in which the medium feed rate was determined by the DOT) were thus inoculated with either the transformed parent or highly branched mutants of the transformed parent to determine whether the reduced viscosity would improve aeration and give higher enzyme yields. The average rate of medium addition was higher for the two highly branched mutants (ca. 8.3 g medium h(-1)) than for the parental strain (5.7 g medium h(-1)). Specific enzyme production in the DOT controlled fed-batch cultures was similar for all three strains (approx. 0.24 g alpha-amylase and glucoamylase [g of biomass](-1)), but one of the highly branched mutants made more total enzyme (24.3 +/- 0.2 g alpha-amylase and glucoamylase) than the parental strain (21.7 +/- 0.4 g alpha-amylase and glucoamylase).

Studies of partially repressed mutants at the tamA and areA loci in Aspergillus nidulans

Mutants, designated tamAr, have been isolated on the basis of simultaneous resistance to toxic analogues thiourea, aspartate hydroxamate and chlorate with L-alanine as the sole nitrogen source. tamAr mutants are also resistant to methylammonium. This resistance of tamAr mutants is correlated with partially repressed activity of a number of enzyme and transport systems regulated by ammonium. Furthermore, tam-Ar mutants have low NADP-glutamate dehydrogenase (NADP-GDH) activity and also efflux ammonium under certain growth conditions. Mutants at the areA locus (areAr) have also been isolated on the basis of resistance to these analogues, with nitrate or L-aspartate as the nitrogen source. These, similar to tamAr lesions, result in resistance to methylammonium and are partially repressed for ammonium repressible system, but in contrast to tamAr, areAr alleles have wild-type NADP-GDH activity and normal ammonium efflux. tamAr and areAr mutants grow as wild type on all nitrogen or carbon sources tested, are recessive, and appear to be epistatic to all other mutations (gdhA1, meaA8 and meaB6) which result in derepressed levels of ammonium regulated system. Whereas tamAr and areAr phenotypes are additive, tamAr is epistatic to areAd phenotype.