Production of Conidia in Submerged Cultures of Penicillium notatum.

Foster, McDaniel, Woodruff, and Stokes (1945) recently described the formation of conidia by molds of the genus Penicillium during submerged growth in liquid culture media. Controlling or associated factors for this phenomenon were described as the presence of a rather high calcium-ion concentration and, in general, the development of considerably less mycelium before spore formation than is found if conditions favor development of the vegetative phase alone. In the course of experimental studies on microbiological problems relating to the production of penicillin, we have observed that submerged conidia formation may be induced in nutrient media of normal calcium concentrations. Media containing nitrogen supplied by ground whole wheat, malted wheat, stillage from yeast-fermented wheat mash, or corn steep water have all resulted in formation of conidia by the submerged mycelium under proper conditions. A typical liquid substrate in which submerged sporulation by Penicillium notatum has been reproduced consists of 25 per cent thin-grain stillage2 and 3 per cent glucose, with the initial pH adjusted to 5.5 with NaOH. When incubated at 24 C and shaken to produce submerged growth, conidia formation was evident in cultures within 48 hours and was heaviest during the fourth and fifth days. The presence of 0.025 per cent MgSO4. 7H20, 0.05 per cent KH2PO4, or 0.004 per cent ZnSO4 7H20 did not noticeably affect the production of conidia, whereas the addition of 0.3 per cent NaNOg resulted in much heavier mycelial growth and only very slight sporulation. Penicillin titers were generally low (20 units per ml or less) in sporulating submerged cultures. Factors favoring conidia formation in submerged cultures on media such as that described above appear to include a moderate amount of growth and the maintenance of an hydrogen-ion concentration in the culture medium of about pH 5.0 to pH 6.5. Only a sparse formation of conidia occurred when vegetative development was sufficiently heavy to interfere with good shaking and, therefore, with good aeration. Extensive sporulation occurred, however, in cultures of slight or moderate growth. The relationship between extent of growth and sporulation is in general agreement with the observations of Foster et at. (1945). The acid medium is usually associated with the presence of readily utilizable carbohydrates, such as glucose, and the accompanying formation of organic acids.