In Bacillus subtilis bacteriophage Phi-29 the DNA molecule is packed after cell division into a hollow shell  by a unique machine.  The way that this machine works was the subject of investigation by a team of scientists.  Competing theories had the machine either rotating the DNA strands as it packed them into the shell, or just pushing them in.  Researchers attached tiny magnets to the ends of the DNA strands to stretch them out, and attached fluorescent tags onto the DNA strands to determine if the strands were being rotated.  The results of the study found no rotation:

How, then, does it happen? The researchers noted that their findings are compatible with a recently proposed nonrotating model in which the ring of ATPases alternately compresses and extends, drawing the DNA in—a bit like what your mouth might do if you had to eat a plateful of spaghetti with your hands tied behind your back.