Studies on synchronously dividing cultures of <i>Euglena gracilis</i> Klebs (strain Z). I. Attainment and characterization of rhythmic cell division

Abstract

Abstract Euglena gracilis Klebs (strain Z) was grown synchronously on an aerated, inorganic salt medium at 25°C under a L D: 16 , 8 or L D: 14 , 10 light‐dark cycle (light intensity of 3,500 lux). In either cycle balanced growth occurred with a doubling of cell number every 24 hr. until limiting conditions of light intensity were reached, due to mutual shading, at about 1.0 – 1.5 × 10 5 cells/ml. An increase of light intensity to 7,000 lux permitted balanced growth to occur to higher cell concentrations, but with no significant change in generation time. With both photofractions, the fission burst during any given cycle began 13–14 hr after the onset of the light period and continued for about 9–11 hour. Synchrony was slightly greater in the L D: 14 , 10 cycle with division confined almost entirely to the dark period; this regime was later adopted for metabolic studies. Synchronous cell division was lost in continuous bright light (3,500 or 7,000 lux), continuous darkness, and in some continuous dim light regimes. The addition of certain organic substrates to the medium resulted in a breakdown of synchrony also, and logarithmic growth ensued. The generation time of cells in either continuous bright light, or with ethanol (0.006 M) and a LD cycle was 11–12 hr.