Although you did not specify the experiment, I assume you are working with growth of microorganisms in presence and/or absence of oxygen. In other words, you are investigating the microbial growth in aerobic (presence of oxygen) and anaerobic (absence of oxygen) conditions. You may have already noticed in your experiment that microbes grow in both aerobic and anaerobic conditions. There are some microbes that can grow in either conditions (presence or absence of oxygen). This means that even without the oxygen, some microbes can grow. Thus, we can hypothesize that planets or moons without oxygen can have some microbial life. You may have also noticed that microbes grow at a faster pace in aerobic conditions as compared to anaerobic conditions. This is true because aerobic cellular respiration produces more energy per unit glucose as compared to anaerobic cellular respiration.
It may also be of interest to know that microbes are probably the first life forms on Earth and the earliest microbes were most likely anaerobes. Thus, we can imagine anaerobic microbes living and thriving in planets and moons that do not have oxygen in their atmospheres.
Hope this helps.