Eukaryota

With your densely packed DNA, you can afford to express a lot more proteins.  There is some serious evolution (without splitting into species) in the next few million years.  In no particular order:

• your DNA stops being stored in a loop.  Instead, you develop end caps called telomeres which act like the bits on the end of shoelaces that stops them unravelling.
• You get bigger.  Much bigger.  
• Instead of 'stealing' genes in the process of eating other chaps similar to yourself, when a pair of you meet up, one 'gives up' some genetic material to the other.

If this last one sounds crazy, because the organism giving up material will lose out, you have to remember that genes are survival machines both in themselves, and in groups.  In this case, the gene may well get the chance to make many more copies of itself when it joins with a new set of partners.

To facilitate all of these things, one major change takes place: the cell wall becomes less thick, and eventually forms a cell membrane.

Additionally, you need to move around - your food demands are so high that you can't just wait around and hope.  To this end, any change which makes you able to move, no matter how small, will be copied around the community.  Eventually, those small changes add up to something called a flagellum.

However, this flagellum needs a lot of energy.  In order to make enough energy, you need to eat, which is done by engulfing smaller things, prokaryotes, until eventually something odd happens...  you eat one, and it survives.  Inside you.  Ewwwww.  The prokaryote inside you lives on, and, protected by you from most other threats, eventually loses the genes it isn't using.  What is left, is a pretty simple thing, no longer an organism, but an organelle.  It's called a mitochondrium.

After all this, finally there is a choice again:

Grow another flagellum?
No thanks, one is enough!