congo red agar can be used for testing biofilm formation in agar, but I am not sure whether electrochemical gradients can be checked by this method.

Thank you Sayan, the problem with red congo agar is that it has been widely discussed its reliability for detecting actual biofilm formation, due to the wide definition of biofilm. Regarding the electrochemical gradients that can be observed, there are some reports of the electrochemical activity of biofilm, including non metal reducers, there would be two different expected results on this setup, there can be either a change in impedance, due to the change within the dielectric layer formed by the biofilm, secondly, there might be changes within the biofilm due to the biological activity, generating different types of reactions that would yield activity regarding ionic transerence and development of redox reactions.

Dear César, 

I don't believe you can test what you want in solid medium. I understand you wanna observe phenomena of chemotaxis in P. aeruginosa and, as i understand, how the availability of certain nutrients/trace elements will affect the biofilm formation... But in solid medium, for example, P. aeruginosa will indeed secret extracellularpolysaccharide  (EPS), which is one of the biofilm basis, but i doubt you can call it a biofilm... 

I work in biofilms with Candida glabrata. Despite my goal is not the same, i understand your issue. I'd say the following. Use a surface for biofilm development, like polystyrene as an example and use liquid medium with different concentrations of the elements you wanna see may be correlated with biofilm formation induction. Then you just compare each result, each biofilm matrix composition and so on... Cause in solid media, you could see swimming and swarming, which means, the bacterial cells traveling to places with higher concentration of the nutrient/trace element, but you can't call it a biofilm...

Hope that helps,

Good luck

Thank you Rui, indeed it can be somehow doubted the statement, however, it has been observed there is electrochemical active behavior on different biofilm communities, that is due to some of the intrinsic activities on the cell surface and on the biofilm layer. It is however one of the experiments that have been planned, there is plenty of information on this respect and it is easy for me to find a suitable liquid media and let the bacteria itself adhere to the electrode surface. It is a very useful approach and I really thank you for your feedback, which in deed helps me keeping in mind that on that respect I might be following a more solid path (Pun intended). I will try to keep this topic updated, so far haven't found any report on media that would help the grouth of P. aeruginosa (there is an interesting paper on this respect with Enterobacter clocae (Evaluation of the Effect of Different Growth Media and Temperature on the Suitability of Biofilm Formation by Enterobacter cloacae Strains Isolated from Food Samples in

South Africa Mirriam E. Nyenje et al. 2013). Thank you again for your insights!

For evaluation of biofilm in Agar you should use the congo red method

You can use Congo red protocol for this matter, if you don't want to use solid media you can apply Crystal violet staining in microtiter platets

Can I use TSB media for biofilm formation ?