The term "soul" seems a bit too abstract.
Perhaps a more appropriate term would be "will."
Chakra can carry will.
This once led Orochimaru, after his defection, to set his sights on the tailed-beasts, but unfortunately, the tailed-beasts were impossible to study; their massive size was enough to deter Orochimaru.
As for the remains of some tailed-beasts, their research value was limited because they were merely clusters of chakra.
Gathering his thoughts, Orochimaru preserved the cell tissues of Shikamaru, Ino, and Choji, devoting all his energy to cloning Sakura and researching Naruto's cells.
"The cells of a Jinchuriki are indeed different from normal people, more vital, but Naruto's cells are perhaps too active?" Orochimaru, through the microscope, observed that Naruto's cell tissues retained the same vitality as a normal person, constantly rubbing against each other and devouring the substances and energy in the nutrient solution, dividing on their own.
