Bacteria, a group that does not use oxygen at the bottom of the bottle is growing. The group that needs oxygen to thrive are thrive on the surface, and the Group was able to thrive in the oxygen, but in small quantities.
Anaerobic bacteria To grow at the bottom of the bottle. Groups that need oxygen to thrive. It grows on the surface of food. And can grow in low oxygen, but need in small amounts.
Bacteria that do not use oxygen. There will be growth at the bottom of the bottle. The aerobe in the growth. Will thrive on the surface of food. And the group can thrive where oxygen but require only small amount.