Defective filamentous and invasive growth of the <i>age3</i>Δ/Δ strain on/in solid media.

Note: All images of each row are shown in the same magnification. (A) The strains SN87 (AGE3+/+), UZ22 (AGE3+/Δ), UZ45 (age3Δ/Δ) and UZ55 (age3Δ/Δ::AGE3) were induced for filamentous growth on Spider agar at 37°C for three and six days (two sets of agar plates). The colonies were photographed and the colony edges inspected under the microscope. To try to remove the colonies after three days of growth one set of agar plates was washed with water. Only the homozygous age3 mutant colonies could be removed easily. At the edges of the mutant colonies after wash single yeast cells and very short filaments are still attached to the agar. However, weak invasive growth into the agar by age3 mutant filaments is only visible in the colony center. After six days, filamentous growth is seen macroscopically for the wild-type, the heterozygous and the reintegrant strain. The mutant strain forms flat colonies without visible filaments (as also seen after three days). (B) The strains mentioned under (A) were induced for filamentous growth by embedding in YPS agar and incubation for three days at 37°C. The homozygous age3 mutant colonies formed after two days of growth show a high rate of filamentation. However, the filaments were unable to develop further (three days) into long filaments which could invade the agar as filaments of the control strains do.