FIG. 4.

Early induction of filamentous mycelia growth. Conidia (10⁶ conidia/ml) were inoculated into 250 ml of CAP medium in 1,000-ml baffled flasks and incubated at 30°C at 250 rpm. A. niger was precultured under citric acid production conditions for 12 h. Thereafter, 1,000 ppb of Mn²⁺ was added to half of the A. niger cultures for induction of filamentous growth while the other half of the A. niger cultures were maintained in CAP medium (10 ppb of Mn²⁺) for pelleted growth. The mycelia were harvested at different induction intervals for microscopic observation and RNA extraction. The photos in the left panels were taken from mycelia harvested from a citric acid-producing culture (pellet growth), and the ones in the right panels were taken from mycelia harvested from Mn²⁺-inducing filamentous growth. All photos were taken at the same magnification (×75). The labels to the right of the panels represent the length of induction.