An example of the Euglena group gathered to the fixed laser beam (Cell density of the culture medium:2600 cells/mm^, After 10 minutes laser irradiation) 

 

 Changes of the density distribution around the laser spot light through the time passage at the population density of 2600 cells/mm^ These group formations are basically by the positive orientation phototaxis of Eu-glena. However, the reason why we cannot see positive orientation phototaxis at the individual cell is not clear. Therefore, low density culture media were used for the next experiments. Fig.6 is an example photograph that was taken after 90 min-utes irradiation of spot laser beam to the 190 cell/mm^ culture medium. The changes of the density distribution around the laser spot light were also summa-rized in Fig.7. The results showed that the Euglena group was formed in the final stage in the case of the low density media, it needs longer time. There is no group after 10 minutes irradiation. Group formation starts after 30 minutes irradiation. 

 An example of the gathering of Euglena to the laser beam at the popula-tion density of culture medium: 190 cells/mm^ taken after 90 minutes laser irra-diation

 That is to say, the reasons why we have not observed positive orientation photo-taxis are these two. (1) Positive orientation phototaxis is a statistic phenomenon based on the photophobic response, and it needs longer time to go to the comfort-able illumination intensity area. Therefore, it has not appeared in one reaction on the above-mentioned observation. (2) The magnification for individual cell reac-tion is too large and we only observed too near area around the laser. As a result, the Euglena only showed the negative reaction. The reason why group formation was accelerated by the population density is con-sidered as follows. High density media have more probability ratio of collision be-tween the Euglena that are swimming to the laser by positive phototaxis and that are swimming against the laser by negative phototaxis. This effect restricted the swimming course; hence, the group formation was accelerated

 Deformation and Transition of Formed Euglena Group

 To apply the formed Euglena group, we have to move and deform the group. It is done by moving the scanning laser beam. If the moving speed of laser beam is too fast, the Euglena group can not catch up with laser. Therefore, we have to limit the moving speed of laser irradiation area. The shape and the condition of the Euglena group to the moving laser spot irradia-tion were investigated to clarify the limit of the moving speed. The culture media that the population density is about 2000 cells/mm3 were used for this experiment. The depth of this experimental pool is also 0.13 mm. The results are shown in Fig.8. The left side photographs show the condition after the 10 minutes irradia-tion of spot laser beam to form the Euglena group. The right side photographs show the resuhs after moving the laser beam to the right down area by the setting speed. The results show that if the moving speed is under 4mm/s, the Euglena group can catch up with the transition of laser beam

Therefore, the deformation of the Euglena group was examined in the next ex-periments. The method is, first, a spot laser was irradiated in the pool. And then, the spot beam was deformed to the circle shape by controlling the galvano-scanner. Then the scanning circle line was gradually deformed to the line. Finally, the scanning line was deformed again to the circle shape. The transition speed is 3 mm/s. Fig.9 shows the continuous photographs from the experimental video im-age. This result shows that we can generate any shapes of the Euglena group if the transition speed of laser is under 4 mm/s. However, to generate the shape of the Euglena group faithfully to the scanning la-ser, we have to prepare shallow pool (< 0.2mm) and high density culture media (> 1000 cells/mm3). If the experimental pool is too thick, the ground which is not ir-radiated by laser was covered by the Euglena and it is difficult to distinguish the shape of the Euglena group

 

 Deformation of the Euglena group by changing the scanning line of laser beam (Pool depth: 0.13mm, Population density: 2000 cells/mm^) 

 Now we can make any shapes of Euglena groups and move them and deform them at our will by above mentioned technology. Therefore, the possibility whether

 these controlled Euglena group can move and manipulate the object or not was in-vestigated. If the Euglena group was hit on the object, the unbalanced force from the collision of so many Euglena to the object might move the object. Therefore, object trans-porting experiments were done by using spot laser beam and high density culture media (Population density: 2000 cells/mm^). Fig. 10 shows an example. In this ex-periment, spot laser was moved to the upward direction. If the condition is within the range, we can manipulate the object by the motion controlled Euglena group. It is very easy for this experimental system to generate the shape of the Euglena group that is fit to the target object. Therefore, a line shaped Euglena group was generated for long rectangle target object. Fig.l 1 is an example. Object transporta-tion can be done more stably by fitting the shape of the Euglena group to the target object