Regulation of Extracellular Acid Protease inMucor Miehei

Understanding the regulation of extracellular protease gene expression in fungi: a key step towards their biotechnological applications

The secretion of proteases by certain species of yeast and filamentous fungi is of importance not only for their biological function and survival, but also for their biotechnological application to various processes in the food, beverage, and bioprocessing industries. A key step towards understanding the role that these organisms play in their environment, and how their protease-secreting ability may be optimally utilised through industrial applications, involves an evaluation of those factors which influence protease production. The objective of this review is to provide an overview of the findings from investigations directed at elucidating the regulatory mechanisms underlying extracellular protease secretion in yeast and filamentous fungi, and the environmental stimuli that elicit these responses. The influence of nitrogen-, carbon-, and sulphur-containing compounds, as well as proteins, temperature, and pH, on extracellular protease regulation, which is frequently exerted at the transcriptional level, is discussed in particular depth. Protease-secreting organisms of biotechnological interest are also presented in this context, in an effort to explore the areas of industrial significance that could possibly benefit from such knowledge. In this way, the establishment of a platform of existing knowledge regarding fungal protease regulation is attempted, with the particular goal of aiding in the practical application of these organisms to processes that require secretion of this enzyme.

Production of alkaline protease by a genetically engineered Aspergillus oryzae U1521

The production of alkaline protease of Aspergillus oryzae U1521 was examined in liquid culture. In a culture of defatted soybean only, it gave satisfactory enzyme yields at 584,000 U/g defatted soybean. When various carbohydrates were supplemented, enzyme production was significantly increased. An increase in production by lactose was the most marked. Enrichment with casitone or casein increased productivity, but not cornsteep solid. Media formulation (g/L) of defatted soybean 10, lactose 5, casitone 1, and KH(2)PO(4) 5 enhanced alkaline protease production by A. oryzae U1521 to a maximum of 1,410,000 U/g defatted soybean. Scaling-up experiments indicated the flask-scale results could be reproduced at 40 g of substrate in 5-L fermenter. The enzyme activity was maximum between pH 8-9 and at a temperature of 45 degrees C.

Regulation of extracellular proteases in Achlya ambisexualis

The use of proteins as a nutrient source by Achlya ambisexualis was investigated, using media containing defined and undefined sources of carbon, nitrogen, and (or) sulfur. Release of extracellular proteases occurred during growth on all proteins and protein hydrolysates tested, but not during growth on yeast extract or in defined medium. In gelatin-containing media, three major bands of extracellular protease activity were detected by electrophoresis, with estimated molecular mass of 26, 48, and 58 kDa. Growth on gelatin was stimulated to a much greater degree by the addition of glucose to the medium than by additions of glutamic acid or methionine. This and the release of ammonia during growth indicate that gelatin is less effective in meeting metabolic needs for carbon than it is in meeting the needs for nitrogen and sulfur. Protease secretion is only partially regulated by glucose, whereas glucose, methionine, and glutamic acid in combination cause almost complete repression. The pattern of regulation indicated by these results is most consistent with one of induction + derepression. Key words: oomycetes, proteinases, regulation, secreted enzymes.

Some physiological studies on fungi isolated from poultry feedstuffs

A total of 506 isolates of mesophilic, thermophilic and thermotolerant fungi isolated from the poultry feed ingredients included soybean meals, ground maize, cottonseed cake, wheat bran and fish meal, on glucose-Czapek's agar, Littman oxgall agar at 28 degrees C and yeast starch agar (YPSs) at 45 degrees C, were screened for their ability to produce hydrolytic protease enzyme on solid media. Most of the fungal isolates were able to produce such enzymes but with variable capabilities. The highest proteolytic activity was exhibited by some isolates of Penicillium chrysogenum, Aspergillus flavus, Thermoascus thermophilus and Rhizopus chizopodifarmis. Of all fungal isolates screened for proteolytic activity, Penicillium chrysogenum and Thermoascus thermophilus produced the highest amounts of proteases. These two isolates were used to study the effect of some environmental and nutritional factors on their proteolytic activity. It was found that the highest yield of protease by P. chrysogenum (12.5 units) was achieved 3 days after incubation at 30 degrees C. Marked reduction in protease activity was observed at 37 degrees C. The thermophilic fungus T. thermophillus exhibited maximum (18 units) proteolytic activity 6 days after incubation at 45 degrees C. The enzyme yield was reduced to 13 units at 50 degrees C. Among the seven carbon sources tested, sucrose was the most appropriate for maximum protease production by both P. chrysogenum and T. thermophilus (13.2 and 12.8 units, respectively). Of the sixteen nitrogen sources investigated, NaNO3 was the best inorganic additive nitrogenous salt which induced the highest proteolytic activity by P. chrysogenum and T. thermophilus, whereas DL-tryptophan was the most preferable organic nitrogen compound for maximum protease production by the two fungi tested.

Characterization and comparison of a Neurospora crassa RNase purified from cultures undergoing each of three different states of derepression

Extracellular RNase N4 from Neurospora crassa is derepressible by limitation of any of the three nutrient elements obtainable from RNA. We have purified and characterized the enzyme from cultures grown under each of the three states of derepression. The purification procedure consisted of an ultrafiltration step, cation-exchange chromatography, and gel filtration. We found only one enzyme (N4) that hydrolyzed RNA at pH 7.5 in the presence of EDTA in culture filtrates from nitrogen-, phosphorus-, or carbon-limited cells. In all three cases, the enzymes were identical by polyacrylamide gel electrophoresis (Mr approximately 9,500) and by gel filtration (Mr approximately 10,000). There were no differences in thermal stability or pH optimum; all three cross-reacted with antibody to the nitrogen-depressed enzyme in interfacial ring and in Ouchterlony tests. Digestion of homopolyribonucleotides indicated that N4 preferentially cleaved phosphodiester bonds adjacent to guanine residues. Results indicate that the enzymes are very similar or identical and are probably products of the same gene. N4 appears to be homologous to guanine-specific RNases from other fungal sources.