alchemy and it doesn't work now or at anytime in the past.
You have to HAVE gold chloride to get gold from this bacteria and gold chloride is produced from (surprise) disolving gold in choride. This bacterium merely cleans off the chloride part. This process can also be done with the chemical potassium bromide.
3 AuCl + 4 KBr → KAuBr4 + 2 Au + 3 KCl
It just happens to be neat that a bacterium can do it too. Thats why gold pooping bacterium is in an art exhibit. Because bacterium pooping gold is ART (I guess....).