Recovery of total microbial RNA from lactic acid fermented foods with a high starch content

An optimized procedure for the recovery of RNA from micro-organisms involved in the fermentation of starchy foods (mainly hard-to-lyse lactic acid bacteria) is reported. Critical steps for the extraction were: cell recovery by differential centrifugation; cell wall digestion with both mutanolysin and lysozyme; and CTAB treatment for the elimination of starch. Digestion of starch with alpha-amylase did not improve extraction yields. The method yielded high amounts of RNA from pozol, a Mexican maize-based fermented food, and was found to extract total RNA efficiently from all the micro-organisms potentially present in these ecosystems. Both rRNA and mRNA recovered were of high quality and suitable for hybridization studies.