Bacteria from acidic to strongly alkaline insect midguts: Potential sources of extreme cellulolytic enzymes

Bacterial isolates from the European Corn Borer (ECB) Ostrinia nubilalis and the coleopteran Colorado Potato Beetle (CPB) Leptinotarsa decemlineata midguts were identified and characterized. Twenty-four colonies, selected on solid media with cellulose as the sole carbon source and pH values ranging from 5 to 12, were identified through 16S sequencing as members of the genera Acinetobacter, Comamonas, Klebsiella, Microbacterium, Micrococcus and Sphingobacterium. A complete enzymatic characterization revealed widespread – albeit moderate – cellulase properties in all but one isolate and high xylanase activity in the four CPB isolates. Different enzymatic patterns in terms of optimal pH, substrate use and degradation times were observed, and several isolates were selected as promising cellulase producers at extreme (pH 12) conditions. Implications of the results for the biotechnological industry are discussed.

► Bacteria from alkaline and acidic insect midguts were studied. ► Isolates grew at pH values ranging from 5 to 12 and exhibited cellulolytic properties. ► Bacteria from the mildly acidic CPB midgut displayed high xylanase activity. ► ECB midgut-associated bacteria exhibited maximum cellulose activity at very high pH. ► These bacteria are promising cellulolytic sources with biotechnological applications.