Soft agar plug assays to determine induction of gelatinase activity.

<p>The effect of (A) 0%, (B) 2% and (C) 4% NaCl on the ability of equal amount of gelatinase biosynthesis-activating pheromone (GBAP) to induce gelatinase activity in a strain lacking GBAP production was assayed using soft agar plug assays. The right hand pocket was filled in with overnight culture of MS253 diluted 100× in TH soft agar. To the left hand pocket, 1∶1 TH soft agar and sterile filtrated supernatant from overnight culture of MS234, a V583 Δ<i>gelE</i> mutant carrying a constitutively expressed version of <i>fsrD</i> for overproduction of pheromone was added. A gelatinase negative pheromone producer was used to exclude an effect of carryover of active proteinase. Gelatinase activity was seen as turbid zones around the right hand pocket after incubation at 37°C for 24 h and 4°C for 1 h. After 24 h incubation the effect of NaCl in growth is annulled, in accordance with <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094571#pone-0094571-g001" target="_blank">Figure 1</a>, and the differences in zone size is therefore a result of ionic interference with the Fsr pheromone-receptor interaction.