Answer:
Due to suitable conditions.
Explanation:
Large population of bacteria can be maintained in the light organ to produce light by providing suitable conditions for growth and development in the organ. The luminescent genes are off when the organ has low cell density while on the other hand, when the density of cell is high in the light organ the luminescent genes automatically turned on and light up the organ. These Vibrio fischeri needs habitat and food for their growth and survival which is provided by the squid. If there is sufficient food for the squid, the population of Vibrio fischeri increases in the light organ.