Dear Ravi, We use small lidded 30 ml glass tubes (Universals) for our biofilm work on pseudomonads (and this should also work for Bacillus spp.). We are interested in air-liquid-solid and air-liquid interface biofilms, rather than the standard submerged liquid-solid interface biofilms most people investigate. If you use these larger tubes as microcosms, it is possible to measure the degree of attachment to the tube walls using crystal violet (this is often the 'biofilm' people measure in micro titre dishes) as well as the strength of any biofilm extending across the liquid surface: we do this by adding small glass balls until the biofilm breaks or sinks. We also measure the tube's OD600 after assessing strength and attachment, as a means of measuring total growth. Statistical analysis can then be used to determine whether growth and attachment are factors in biofilm strength etc. Regards, Andrew.