You can use a stainless steel container without negative affects for your live sourdough starter. However, the acids from the sourdough starter can leech into other types of metals causing toxins to enter your sourdough starter. So stick with stainless steel or a glass jar to be on the safe side.
Other metals might be okay with very little exposure to your sourdough starter, but I would just steer clear of them to be safe.
For making sourdough bread, it is safe to use a stainless steel metal mixing bowl for mixing and proofing.
