Since agar is made up of Agarose (which is a polysaccharide polymer containing Carbon units). Suppose we are trying to isolate any bacteria which can grow only on the carbon source provided by us (any Aromatic Hydrocarbon) on Agar plate supplemented with salts and the selected carbon source. So, can it be possible that the bacterium is taking the carbon from the Agar instead of the compound that we have added in the media?
Dear Deepak Rawat,
My suggestion is:
If you are taking an agar and supplementing it with the nutrients that are required by that specific bacteria, then it will enhance the chances of that bacteria growing before any other. However, if you are talking about nutrient agar, which is an all purpose medium, there might be very little selectivity because all other ingredients would still be there.
If the bacteria grows by that specific carbon and your selective medium have it, the bacteria would utilize that specific carbon first before any other alternative. Just have the right concentration to keep a conducive environment for the bacteria.
Agar itself can come in different purities, and it is conceivable that some may contain enough carbon-based organic impurities to support a small amount of bacterial growth. Furthermore, there are some bacteria, notably marine bacteria, that produce agar-degrading carbohydrases, and utilize the resultant galactose as a carbon source. this should be readily observable by degradation of the agar gel, seen as pits or holes in the agar.
There are certain bacteria and fungi that can use agar as a carbon source. To exclude that you can prepare plates with silica gel. Also make sure you don't get autotrophs capable of fixing carbon dioxide by scrapping all CO2 from the atmosphere they are growing in.
Thank you very much for your valuable comments. I am planning to grow bacteria on a media devoid of any carbon source, for that i have selected Bushnell Haas (BH) media supplemented with the aromatic compound in which i am interested. For the experiment i used BH without my compound as a control but i noticed some growth on the BH agar plates. So, i was wondering that could it be because of the agar or some other impurities!!!
As Hedda said, agar could be used as carbon source by bacteria. If your strain could use agar as carbon source, they usually form depression around the colony. Also, when we talk about 'agar', usually commercial agar is a mixture. If you are strict about carbon source, use agarose will be a better idea.
You can check the bacterial growth on agar plate devoid of any carbon sources. Several marine bacteria are agarolytic in nature and uses agar as carbon source. The agar degrading/utilizing bacteria forms craters or clearance zone around the bacterial colonies which could be easily observed and agarolytic bacteria can be identified. However, agar degrading zone or craters could be visualized by pouring the lugol's iodine solution on the plate. Alternatively you can use the Gelrite as a solidifying agent instead of agar.
https://link.springer.com/chapter/10.1007%2F978-981-10-1044-6_12
Thank you Raj Morya for suggesting this interesting paper. I will go through this paper.
I would suggest using Bushnell Haas broth overlaid by your hydrocarbon source
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