Hi Subburamu,

I'm afraid I'm not an expert in this area, but can make a few quick suggestions.

I know that there are incubators available on the market that are airtight (i.e. in which you can control the exact mixture of gases); however, they tend to be very expensive. Depending on what gases you want in contact with the bacteria, you could always use a heavier-than-air gas to float a layer over them (e.g. Nitrogen); however, that will obviously eliminate other gases (in particular, Oxygen!) as well.

The final option might be to grow them in an airtight container containing some kind of CO2-scavenging catalyst or device? This would require a bit of looking into carbon capture technology etc. which I know nothing about, but a quick Google search suggests things like KOH:

http://www.ncbi.nlm.nih.gov/pubmed/16047775

Hope that's useful!

Dan

P.S. Or you could just grow them at -100 degrees Celcius so the CO2 crashes out as dry ice . . . simple! ;)

to eliminate atmospheric CO2 you may used the classical experimental design of plant physiologists when they wanted to demonstrate the need of CO2 to photosynthesis : before entering the culture flask, the air flow was passing through a solution containing baryte or Ca(OH)2 that sequestered CO2. An aquarium air pump is a simple device to control the air flow.

We used to use air-tight jars that you place your cultures in and then flush with whatever mix of gas you want them to grow. After 30 minutes or so close the vent and intake.