Figure 1: Gelatin hydrolysis test. After 30 minutes in an ice bath, the nutrient gelatin tube inoculated with Bacillus subtilis exhibited positive gelatin hydrolysis as shown by medium liquefaction. Gelatin hydrolysis was observed after 3 days of incubation. (Thomas Edison dela Cruz and Jeremy Martin O. Torres, University of Santo Tomas, Manila, Philippines)
Figure 2: Gelatin hydrolysis test. After 30 minutes in an ice bath, the uninoculated control remained solid. (Thomas Edison dela Cruz and Jeremy Martin O. Torres, University of Santo Tomas, Manila, Philippines)
Figure 3: Gelatin hydrolysis test. Gelatin hydrolysis test using the nutrient gelatin plate method. Positive gelatin hydrolysis exhibited by Bacillus subtilis (A) is indicated by the clear zone around the colony after the addition of saturated ammonium sulfate. Negative gelatin hydrolysis exhibited by Escherichia coli (B) is indicated by the absence of a clearing zone around the colony. Inoculated culture plates were incubated for 24 hours. (Anne Hanson, University of Maine, Orono, ME)
Figure 4: Gelatinase. Pseudomonas aeruginosa (top), Escherichia coli (middle), and Serratia marcescens (bottom) were inoculated into gelatin agar and incubated for 1 week. The agar in the Pseudomonas aeruginosa and Serratia marcescens tubes remained liquid after incubation and icing, indicating digestion of gelatin by the exoenzyme gelatinase. The Escherichia coli culture exhibited solidified agar after icing, indicating that gelatinase was not produced. Note: red color in the agar is pigment produced by Serratia marcescens. (Tasha L. Sturm, Cabrillo College, Aptos, CA)
Figure 5: Positive and Negative Gelatinase Activity Produced by Serratia marcescens and Micrococcus roseus. Gelatin (BD Difco) was inoculated using the stab technique and an inoculating needle. Tube A was inoculated with Serratia marcescens and tube B was inoculated with Micrococcus roseus. Both tubes were incubated at 25°C for 24 hours followed by refrigeration for 30 minutes. Note the liquification of the gelatin in tube A by Serratia marcescens which indicates the presence of the enzyme gelatinase. The gelatin in tube B is still solid which indicates no gelatinase produced by Micrococcus roseus. (Janie Sigmon, York Technical College, Rock Hill, SC)
Figure 6: Positive and Negative Gelatinase Activity Produced by Serratia marcescens and Micrococcus roseus (Labeled view) (Janie Sigmon, York Technical College, Rock Hill, SC).
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