I have been a childminder for ten years and have never used the word 'naughty' in behaviour management. Don't use a naughty step, mat ether.
First of all, does your son have other developmental issues? Sit down with the nursery to see about that. Speech? Does he get angry? Why do you think he bites? Usually children start biting out of frustration, another child will 'invade' their space, a nursery can be a busy and chaotic place. Is it tiredness? How is his sleep?
Then, it becomes a habit. He gets attention from it - and negative attention is better than no attention. Is the staff paying attention to him for positive behaviour? Do they play with him one-to-one?
Also, one of the thing that really works is to pay attention to the other child. Say your son bites, then the staff member should say to him a very firm NO. And I mean VERY firm. look at him in the eyes, and not in a shouty voice, but a firm, loud, deep voice.
Then they should pay a lot of attention to the other child, almost over the top. Then they have to get your son to apologise - even if he doesn't speak yet he should be able to feel understand if someone explains it to him clearly that we don't bite, because it hurts.
Then attention towards him aimed at distracting him, playing in a positive way. If the staff knows that he is biting they should hover over him a lot and make sure they can prevent it. You need to break the cycle and stickers won't work at that age. Not for this.