微藻光密度与细胞密度及生物质的关系

以四种常见微藻,小球藻(Chlorella sp.XQ-20044)、栅藻(Scenedesmus sp.SS-200716)、绿球藻(Chlorococcum sp.)和螺旋藻(Spirulina sp.CH-164)为实验材料,用梯度稀释法测定对数生长期不同浓度藻液的光密度(OD)、细胞密度和生物质干重(DW),在光自养分批培养模式下对4种微藻进行OD-波长(350—800 nm)扫描,同时测定细胞密度和生物质干重,分析藻液OD与细胞密度、生物质干重的关系。结果表明:在任何波长下,对数生长期的4种微藻细胞密度与OD值、生物质干重与OD值的变化都不成比例,波长不同其拟合曲线偏离直线的程度不同。但是,在435 nm处这种关系最接近直线,可以用直线方程近似描述(R20.98),其它波长处细胞密度-OD、干重-OD的关系都可以用二项式方程很好地描述(R20.99)。因此,光密度法适用于连续和半连续培养,可以用435 nm处测得的OD值计算细胞密度与干重。但是在分批培养模式下,4种微藻DW/OD比值随着培养时间均逐渐上升。小球藻DW/OD540为0.19—0.44 g/L,栅藻DW/OD540为0.36—0.53 g/L,绿球藻DW/OD540为0.48—0.75 g/L,螺旋藻DW/OD560为0.46—0.74 g/L,因此分批培养模式下采用测定藻液OD值反映细胞密度和生物质的方法不适用,只有直接测定细胞密度和生物质才是准确的。研究结果为正确使用分光光度法监测微藻生长提供依据。

The relationships between optical density, cell number, and biomass of four microalgae

To establish spectrophotometry as a method for estimating cell number and biomass of microalgal cultures, the relationships between optical density (OD), cell number, and dry weight (DW) were investigated for four familiar algae, Chlorella sp. XQ-20044, Scenedesmus sp. SS-200716, Chlorococcum sp. and Spirulina sp. CH-164. Algal suspensions with different cell concentrations were obtained by serial dilution of cultures in exponential growth, and their ODs determined by scanning at wavelengths from 350 nm to 800 nm. The cell numbers were determined by cell counting, and biomass (as DW) was determined by weighing. Further, the ODs of the autotrophic batch cultures were scanned during the growth process, and correlated with cell numbers and DWs of the same samples. The results were as follows: for the four microalgae, cell numbers and biomass-dry weight did not change linearly with the changes in OD at all the wavelengths examined. However, the relationships could be approximately described by a linear regression equation (R² > 0.98) at 435 nm, and were well described by binomial regression equations (R² > 0.99) at other wavelengths. In continuous and semi-continuous cultures, the OD at 435 nm was suitable for estimating cell number and biomass; however, in autotrophic batch cultures an increase of the DW to OD ratio was observed during culture growth for all four algae. The ratio (DW/OD) was 0.19 to 0.44 g/L for Chlorella, 0.36 to 0.53 g/L for Scenedesmus, 0.48 to 0.75 g/L for Chlorococcum and 0.46 to 0.74 g/L for Spirulina. Thus, spectrophotometry was not suitable for estimating biomass-DW in batch culture. This study should help guide the proper application of spectrophotometry in microalgae culture.