Why not to google before asking? See

http://pubs.acs.org/doi/full/10.1021/acs.chemrev.5b00407

Thanks for the references. I am wondering that can superoxide free radicals be synthesised under anaerobic conditions by bacteria? As we know, the formation of superoxide free radicals are associate with the reduction of oxygen under aerobic conditions.

Theoretically it's possible from H2O2 (read the review I recommended). While H2O2 is also formed from O2. I doubt that it can be formed by anaerobic bacteria, but who knows?

Hi your question is not precise enough. In which medium do you want to synthesize O2-? in cells? which ones? what is the aim of it? yes it is possible from H2O2 but you need some one electron reductant with it. otherwise you may use photolysis of radiolysis of H2O2.

I think you can use Xanthine and xanthine oxidase. for more introduction Sun et al. (1988) Superoxide dismutase metod.

Dear Wang,

Excellent reviews have been suggested on various aspects of superoxide anion radicals and other ROS.

Regarding the your query regarding if superoxide anion radicals can be produced under anaerobic conditions, I doubt. In general, at least in plant systems superoxide anion radicals are generated due to one electron reduction of oxygen. These radicals are most abundantly produced in chloroplasts as oxygen is invariably generated as a by-product during photosynthetic light reactions. Superoxide anion radicals are generated excessively under any stress that leads to an increase in NADPH to NADP+ ratio. Therefore, I doubt the generation of superoxide anion radicals under anaerobic conditions. But, we cannot 100% rule out the possibility - may be oxygen in organic skeletons of organisms, if released may contribute to superoxide anion radicals (but I highly doubt such a possibility). Yes, I do completely agree that hydrogen peroxide can generate superoxide anion radicals through various ways.

However, I request Prof. Yurii V Geletii with his immense expertise in this field to educate us further on this topic.

Ask an interesting question and I'll be happy to answer