Monoderm Spore Engulfment
Once the septum is in place, it is then extended, as you can see in this Bacillus subtilis cell, enlarging the nascent spore and ultimately separating it from the mother cell envelope. Note that the monoderm mother is producing a diderm spore, surrounded by two layers of its mother’s membrane. As this occurs, a copy of the genome is pumped through a specialized protein nanomachine. The increased turgor pressure from the highly-concentrated DNA helps the forespore round and expand. Usually, the mother cell membrane finishes closing off at the cell pole, but occasionally this occurs instead on the side of the mother cell (⇩).
When the process of engulfment is finished, the forespore’s cell wall is reinforced and expanded into a tough “cortex,” and an extra protein coat is added to the outside, completing the sturdy envelope that will protect the spore from harsh environments (⇩). Finally, when the spore is ready, the mother cell lyses, releasing the time capsule to its fate.