Iodine solution was added to the water with green euglena, the mixture turned blue, why?

Euglena green is mixotrophic, that is, it eats like an animal and a plant – in other words, heterotrophic and autotrophic. Therefore, this organism can form glucose in the light, which is deposited in its cell in the form of a complex carbohydrate. And as you know, complex carbohydrates, when interacting with iodine, can create a blue-violet color in the environment in which they are located. For this reason, the water, where green euglena live, can turn blue when iodine solution is added to it.