This study investigated the physiological and morphological responses of the marine diatom Chaetoceros sp. strain CHX1 when cultured under two contrasting nutrient conditions: nutrient-rich f medium and nutrient-limited f/5 medium. Growth curves showed no significant differences in specific growth rate during the exponential phase; however, final cell densities were higher in f medium. Over culture time, cells exhibited increased biovolume and changes in shape, particularly in f/5 medium, where a subpopulation of spherical cells emerged during the late stationary phase. Pigment content, including chlorophylls a and c and total carotenoids, varied significantly across growth phases and media, with nutrient limitation promoting pigment accumulation as a potential stress response. Photosynthetic performance—assessed via relative electron transport rate (rETR), efficiency (α), saturation irradiance (I k ), and maximum quantum yield (F v /F m )—was highest during exponential growth and declined under nutrient limitation. F v /F m was particularly sensitive to nutrient stress, showing consistently lower values in nutrient-limited (f/5) cultures compared to the full-strength (f) medium across all growth phases. Chaetoceros sp. exhibited pronounced morphological and photophysiological plasticity in response to nutrient availability and culture duration. Under nutrient limitation (f/5), cells developed larger biovolume, spherical morphology, elevated carotenoid levels, and reduced photosynthetic efficiency—traits associated with stress acclimation and the onset of dormancy. The formation of resting cells represents a novel response for this strain, suggesting that controlled nutrient limitation may serve as a tool for diatom preservation, with applications in aquaculture and biotechnology.
Fierro et al. (Thu,) studied this question.