I have done a few kettle sours and in some cases, a wild yeast or heterofermentative bacteria ferments out quite a bit of the sugars. In the past, I've used DME to bring the gravity back up for the boil, but it would be good to have the option of just skipping the boil, however, there's way too much DMS in the wort at this point.
Yes there are sulphate-reducing bacteria. These are mostly found in marine biology. I don't know of any of these bacterium useful in brewing though (maybe just ignorant).
In your case DME will have low SMM and DMS, because it has already been mostly boiled out in proccesing. Though I would still do a short boil 5min boil and chill for sanitation.
Fun Facts Some yeast can convert DMSO into DMS.
DMS can be scrubbed with cO2.
DMS can be perseived with at very low levels.
DMS at high levels can smell and taste like shrimp / seafood water.
DMS has half life of 40 minutes at it's boil temp (99 21°F) so a 90 minute boil or wort usually is enough to get the levels below the detection threshold of most palets.
Once DMS turns into DMSO it can't be boiled off. Its boil temp is > than waters.