Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, United States.
School of Freshwater Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, United States.
PeerJ. 2022 Jul 21;10:e13776. doi: 10.7717/peerj.13776. eCollection 2022.
Many studies have shown that algal growth is enhanced by organic carbon and algal mixotrophy is relevant for physiology and commercial cultivation. Most studies have tested only a single organic carbon concentration and report different growth parameters which hampers comparisons and improvements to algal cultivation methodology. This study compared growth of green algae and across a gradient of photoautotrophic-mixotrophic-heterotrophic culture conditions, with five acetate concentrations. Culture growth rates and biomass achieved were compared using different methods of biomass estimation. Both species grew faster and produced the most biomass when supplied with moderate acetate concentrations (1-4 g L), but light was required to optimize growth rates, biomass yield, cell size and cell chlorophyll content. Higher acetate concentration (10 g L) inhibited algal production. The choice of growth parameter and method to estimate biomass (optical density (OD), chlorophyll fluorescence, flow cytometry, cell counts) affected apparent responses to organic carbon, but use of OD at 600, 680 or 750 nm was consistent. There were apparent trade-offs among exponential growth rate, maximum biomass, and culture time spent in exponential phase. Different cell responses over 1-10 g L acetate highlight profound physiological acclimation across a gradient of mixotrophy. In both species, cell size vs cell chlorophyll relationships were more constrained in photoautotrophic and heterotrophic cultures, but under mixotrophy, and outside exponential growth phase, these relationships were more variable. This study provides insights into algal physiological responses to mixotrophy but also has practical implications for choosing parameters for monitoring commercial algal cultivation.
许多研究表明，有机碳会促进藻类生长，并且藻类混合营养对于生理学和商业培养都很重要。大多数研究仅测试了单一的有机碳浓度，并报告了不同的生长参数，这阻碍了比较和改进藻类培养方法。本研究比较了绿藻在光自养-混合营养-异养培养条件下的生长情况，共测试了五个乙酸盐浓度。使用不同的生物量估计方法比较了培养物的生长速率和生物量。当以中等乙酸盐浓度（1-4 g/L）供给时，两种藻类的生长速度都更快，生物量也更高，但需要光照才能优化生长速度、生物量产量、细胞大小和细胞叶绿素含量。较高的乙酸盐浓度（10 g/L）会抑制藻类的生产。生长参数和生物量估计方法（光密度（OD）、叶绿素荧光、流式细胞术、细胞计数）的选择会影响对有机碳的明显反应，但使用 OD 在 600、680 或 750nm 是一致的。在指数生长率、最大生物量和指数生长阶段所花费的培养时间之间存在明显的权衡。在 1-10 g/L 乙酸盐范围内，不同的细胞反应突出了混合营养过程中深远的生理适应。在这两种藻类中，细胞大小与细胞叶绿素的关系在光自养和异养培养中受到更严格的限制，但在混合营养条件下，以及在指数生长阶段之外，这些关系更加多样化。本研究提供了关于藻类对混合营养的生理反应的见解，但对选择监测商业藻类培养的参数也具有实际意义。
