Why did my Bacteria Turn Black?

Question

I grew a few agar plates with bacteria on it, and the ones that I put in an environment of 37 degrees Celsius, the bacteria which was originally a light whitish yellow turned a very black grey. The bacteria on the other agar plates, that I put in lower tepmeratures, didn't experience such severe colour change and only went to a grey yellow but not black. What would've affected this colour change, and specifically please explain how?

Answer 1

Chances are, the black is the waste product you are getting from your cultures.  And heres why there is a difference in the temps.

Bacteria will grow a lot faster in warmer temperatures. 37 C (98 F), is  is in the optimal range for bacterial growth.  On that (those) agar plates, the growth is so much higher than the ones at lower temperatures, therefore there is more bacteria consuming the nutrients on the agar, and more waste products.  

If you give the cooler plates a few more days to grow and mature, you will find black start to develop as well.

I hope this makes sense... if not shoot me an E-mail

Answer 2

what kind of bacteria r u culturing....minght be the secondary product of the bacteria itself...certain bacteria produce H2S that is black in colour...so the question here is what kind of bacteria your culturing?

doing many biochemical test on the bacteria and rapid test like API 20 will help you determined what kind of bacteria u isolate or culturing....