QUANTIFICATION OF &ITTETRADESMUS OBLIQUUS&IT (CHLOROPHYCEAE) CELL SIZE AND LIPID CONTENT HETEROGENEITY AT SINGLE-CELL LEVEL

Much of our current knowledge of microbial growth is obtained from studies at a population level. Driven by the realization that processes that operate within a population might influence a population's behavior, we sought to better understand Tetradesmus obliquus (formerly Scenedesmus obliquus) physiology at the cellular level. In this work, an accurate pretreatment method to quantitatively obtain single cells of T. obliquus, a coenobia-forming alga, is described. These single cells were examined by flow cytometry for triacylglycerol (TAG), chlorophyll, and protein content, and their cell sizes were recorded by coulter counter. We quantified heterogeneity of size and TAG content at single-cell level for a population of T. obliquus during a controlled standard batch cultivation. Unexpectedly, variability of TAG content per cell within the population increased throughout the batch run, up to 400 times in the final stage of the batch run, with values ranging from 0.25 to 99 pg center dot cell(-1). Two subpopulations, classified as having low or high TAG content per cell, were identified. Cell size also increased during batch growth with average values from 36 to 70 mu m(3) center dot cell(-1); yet cell size variability in creased only up to 16 times. Cell size and cellular TAG content were not correlated at the single-cell level. Our data show dearly that TAG production is affected by cell-to-cell variation, which suggests that its control and better understanding of the underlying processes may improve the productivity of T. obliquus for industrial processes such as biodiesel production.