Hi Vlad, I'm not a doctor or a scientist, but from my understanding as a baker, the acidity present in a mature sourdough starter should discourage botulism. This type of bacteria is rare, and is most likely to occur in low-acid home canned goods that aren't canned properly. When you're creating a sourdough starter from scratch, I don't recommend using the sourdough discard for the first several days. During this period the starter is slowly building in acidity and weeding out unhelpful bacteria. Once the starter is beginning to rise predictably and has a pleasant aroma, then it's safe to use in your baking. I don't recommend consuming raw starter, and if you starter develops mold or an orange or pink streak/tinge, it is usually best to discard it. Feeding your starter regularly will help keep it healthy and active. For our starter routine we recommend feeding your starter twice a day when you have it stored at room temperature, and once a week when it's stored in the refrigerator. If you're not planning to bake with your starter, but want to feed it and return it to the refrigerator, be sure to give it a few hours at room temperature to start bubbling, which will help ensure that your starter develops enough acidity while stored in the refrigerator. 

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