Reducing inconsistent cellulolytic screenings during the Gram’s Iodine Assay

Gram’s Iodine Assay is currently used to detect endoglucanase, a cellulase enzyme which cleaves β-1,4-glycosidic bonds in carboxymethylcellulose (CMC). When a zone of degradation was observed around non-cellulolytic Escherichia coli JM109 with the use of Gram’s Iodine, the assay was further examined. Additional cellulolytic bacteria were chosen to display these inconsistencies. Bacillus thuringiensis subsp. Kurstaki (Btk) and Cellulomonas persica, known to possess endoglucanase, were incubated at 30 °C for 48 h on several different media; 1.5 % agar only, Davis minimal media, CMC agar, non-CMC agar, and Phytagel CMC. After the incubation period all plates were flooded with Gram’s Iodine for 3–5 min. A clear ring of degradation was identified around colonies in plates containing no cellulose and plates containing agar only. When agar was removed as the solidifying agent and substituted with Phytagel, zones of clearing around cellulolytic organisms were altered. These findings indicate that agar alone can cause additional artifacts and should be replaced by other solidifying agents as well as supplementation of the Congo Red Assay. Taking these precautions can overcome inconsistency problems for future cellulolytic screenings.