Fig 1. Tolerance to formic acid of Saccharomyces spp on solid medium using (A) YPD media with formic acid 0 and 35 mM; (B) YNB media with formic acid 0 and 20 mM.

Aliquots 5 μL from tenfold serial dilution yeast cultures (initially suspended to an OD of 1.0 with an estimated cell number of 10⁷ cells/mL) were spotted on the plates. Plates were incubated at 30°C under anaerobic conditions for 48 hours. The last concentration of formic acid that cell growth can be observed was defined as tolerance level.