Nikkomycin Z counteracts Rylux BSU and Congo red inhibition of Saccharomyces cerevisiae growth but does not prevent formation of aberrant cell walls.

Rylux BSU and congo red bind to chitin, interfere with proper cell-wall assembly, and stimulate chitin synthesis by increasing, most probably, chitin synthase 3 (ChS3) levels in Saccharomyces cerevisiae. On the other hand, the antibiotic nikkomycin Z inhibits chitin synthesis competitively. As ChS3 is the critical target of nikkomycin Z, its effect was tested in cells inhibited in growth by Rylux BSU or Congo red. Nikkomycin Z counteracted this inhibition but did not counteract aberrant cell-wall formation. These results indicate that chitin synthesis stimulation is the key step in Rylux BSU and congo red inhibition and support the idea that increase in chitin synthesis represents a compensatory response to damaged cell-wall structure. As Rylux BSU and congo red bind to newly synthesized chitin, further damage is caused in the wall and the response works in this case contrariwise. Nikkomycin Z breaks this vicious circle by counteracting the chitin synthesis stimulation.