Temperature effects on growth and biochemical composition of Chlorella vulgaris under heterotrophic cultivation

Temperature, despite being one of the key environmental factors influencing the physiology and metabolism of microalgae, is often overlooked. Most studies investigating temperature effects in microalgae mainly focus on phototrophic cultivation where the combined effects of light and temperature make it difficult to attribute observed physiological and biochemical changes effects to temperature alone. In contrast, heterotrophic cultivation, which relies on organic carbon sources and grow without light, allows a more direct assessment of temperature effects. However, studies investigating the influence of temperature on microalgae under heterotrophic conditions are extremely limited. However, investigations on how temperature influences microalgae under heterotrophic conditions are limited. In this study, the growth, biochemical composition, and fatty acid profile of Chlorella vulgaris across a broad temperature range (4-35 °C) under heterotrophic conditions were first investigated. The results showed that growth was optimal at 25-30 °C, while it was strongly inhibited at 35 °C. Temperature had significant effects on biomass composition: lipids were enhanced at high temperatures (30 °C, 35.49 ± 3.58%), pigments accumulated at low temperature (4 °C, 16.33 ± 2.93 mg/g DW), while proteins and carbohydrates peaked under moderate temperatures (15 °C, 18.71 ± 1.51%, 49.33 ± 1.74%, respectively). Fatty acid composition was temperature dependent, with monounsaturated fatty acids decreasing at higher temperatures, and polyunsaturated fatty acids showing opposing trends (especially C18:2n6c and C18:3n3), and saturated fatty acids remaining relatively stable. These findings highlight the physiological plasticity of Chlorella vulgaris under heterotrophic conditions and provide new insights into the thermal regulation of microalgal metabolism, with valuable implications for industrial biotechnology.