Characterization Of Morphology And Motility Behavior Of Crypthecodinium Cohnii

Crypthecodinium cohnii has attracted much attention due to its high yield of DHA,but most of its research is on fermentation,while studies on morphology and motility behavior are relatively rare.In this thesis,microscopic tracking technology is used to study the morphology and motility behavior of C.cohnii in its life cycle through real-time observation.This study can deepen our understanding on the physiological activities of C.cohnii and help to develop new methods to improve DHA production.In the study of the morphology of C.cohnii,the division behavior and the lipids in the cells after Nile red staining were observed by inverted fluorescence microscopy.C.cohnii typically shows two types of morphology corresponding to two stages: cystic cells and swimming cells.Cystic cells are round and have no flagella,while the swimming cells are generally elliptical with two different flagellas.In addition,cells with a higher oil content are more opaque and more drop-like appearance on the outside of the cell body.Scanning electron microscopy was used to observe C.cohnii cells prepared by traditional sample preparation method and template-based silica replication method,in order to better understand the details of external surface structure.Currently spherical cell bodies and broken flagellas are observed.In the study of the motility behavior of C.cohnii,based on the two-dimensional projection of its trajectory,the motility behavior can be categorized into five types of motility modes: wave motion,reverse motion,turning motion,and straight motion and rotate motion.Among them,the wave motion has the highest probability of occurrence,and its rotation period is 0.2-0.6 s.In the wave motion,cells tends to rotate clockwise with a faster rotation rate than counterclockwise.It’s trajectory typically shows relatively large radius of curvature and small turning angles.In the reverse motion,cells suddenly turn around and start moving along the opposite direction to that of the original movement.According to in which plane the reversal happens,the reverse motion can be classified into vertical reverse,horizontal reverse and other direction reverse.The probability of occurrence for these three reverse modes is about same.The turning motion shows a turning angle of less than 120°in a two-dimensional plane.The rotate motion tends to rotate clockwise with a radius of rotation less than 20 μm.Both the rotate motion and the straight motion have a low probability of occurrence.Among the five modes,the straight motion has the largest average speed(about 220 μm/s),while the rotate motion has the smallest one(about120 μm/s).By plotting MSD(Δt)in a log-log plot,we found that at short time scales all motility modes show a linear relationship,while the rotate motion and the reverse motion show fluctuations at longer timescales.By calculating the slope of MSD curve in the log-log plot at short time scales,we found that the straight motion is largest with a slope of 1.9392,while the rotate motion is smallest with a slope of 1.6293.But they are all bigger than 1,indicating that they were hyper-diffusion.This is as expected for active systems.In addition,the wave motion,the straight motion and the turning motion are observed to advance while cells spinning,which indicate that they move in a spiral-like way in 3D.It can be seen that the movement is different and their performance is also different.