4C is when water is most dense and is not so low as to cause ice crystal formation.
For short term storage bacterial cultures are often simply kept in a fridge at 4C. I guess that this significantly slows their metabolic rate and so 'stores' them.
However can this be explainded more scientifically? Do the bacteria become 'dormant' or do they pause their cell cycle (become quiescent) at this low temperature?
Basically what are the cellular consequences to the cells of being stored at 4C?