Mycoplasmosis is certainly a possibility, but I think it might be a bit soon to be worrying about that, considering they have only been in their new home for one day?
I agree with xampx that it would be wise to read up a bit on the different problems that rats can have - it will certainly help you know what to look out for and to know when you need to start worrying. As you get to know your rats you will also learn to recognise when something is not quite right. For now, though, in my opinion, I wouldn't panic just yet.