I had the same problem(s). It doesn't look like anything is eating your leaves, believe it or not. The leaves are actually not developing correctly. The good news is, its treatable and the black stuff is not causing the problem. Your plant is simply lacking minor nutritional elements. As far as the black stuff. whether that is B.Sig or not, I don't know, but it seems that Copper Sulfate is the best treatment for most black leaf streak and leaf spot symptoms including viral and bacterial.
You can see the same black fungus infecting the veins first as the symptoms first appeared on my plant.
First, the best thing to do is cut those lower-two infected leaves off and dispose of them far away from your compost and banana plants.
Next, get a good Nutritional spray with Minor elements and no fertilizer-NPK component in it. The minor elements in a foliar will be absorbed by the plant more quickly than the roots (do not apply to root zone). The minor elements are very important to the health of the leaf. A healthy leaf will have stronger resistance to future problems. (wait a few days before applying the copper)
Next, give your plants a good spraying with copper sulfate according to the directions on the label. You can buy it at HD for one. When I sprayed my plants, I got all the leaves but took care to avoid getting any down into the pseudostem--where the new leaf comes out. You can find the copper sulfate and a nutritional under the same brand name at HD. They are somewhat expensive but absolutely worth the cost.
I saw results from the nutritional in less than two weeks. Instead of applying once according to the label, I diluted it to half the recommended rate and applied it twice in the same week. I applied it late afternoon/early evening and then in the morning for the second application. The next leaf to emerge after applying the nutritional had more leaf area but was still wavy. The second leaf had no more holes or splits but it didn't want to open like it should and remained partially rolled. The third and forth leaves have come out with no problems and they are nearly doubled in size and much more wind resistant then the earlier leaves.
Good luck with your nanners, and check back here frequently to see what the other members have to say too!
Chris in FL.