Production of chlamydospores of the nematode-trapping Duddingtonia flagrans in shake flask culture

Duddingtonia flagrans was grown in shake flask culture on Sabouraud's dextrose medium with and without the addition of agar (to form a slightly more viscous medium). The addition of agar increased the number of chlamydospores produced in late stationary phase, with 8.6×105 chlamydospores ml−1 being obtained on a medium containing 5 g agar l−1. The pH optimum for growth was between 5.5–7.5 but colonies formed on plate cultures buffered at pH 10.5. When grown in shake flask culture at 25 °C and pH 7 on malt extract–yeast extract–peptone–glucose medium (MYPG), D. flagrans had a specific growth rate of 0.21 h−1 (doubling time 3.3 h) and produced 5.1±0.07 mg biomass ml−1. To increase chlamydospore production in a liquid medium, D. flagrans was also grown in a two phase culture system in which late exponential phase biomass produced in MYPG medium was transferred to Vogel's mineral salts medium containing various nitrogen (mycological peptone, casein) and carbon (sodium acetate, starch and glycerol) sources. The highest chlamydospore concentrations (6.2×105 and 5.6×105 ml−1) were observed when the biomass was transferred to Vogel's medium containing 10 g starch or glycerol l−1, respectively.