Molecular identification of Lactobacillus plantarum isolated from fermenting cereals

Abstract

The identification of a microbial isolate to genus level only amounts to a partial characterization of the isolate, but this can tell us a lot about that organism. Knowing the species allows the laboratory access to the body of knowledge that exists on that species. Identification schemes using phenotypic characteristics such as colony and cell morphology, Gram reaction and other staining characteristics, nutritional and physiological requirements for growth and metabolic characteristics have been developed and improved over many decades to a point where laboratories are able to identify isolates to species level using simple conventional methods. This phenotypic method however have some limitations apart from being laborious and time consuming, some organisms may however be misidentified either at genus or species level. This work aims at looking directly at the genome of lactic acid bacteria (LAB) and from this identifies some species using its genotypic and phenotypic characteristics. These bacteria species were identified by sequencing specific sections of ribosomal DNA - the 16S rRNA gene, after amplification by PCR, and then comparing the results to sequences stored on a related database. The results from both conventional and molecular methods were then compared. Twenty (20) Lactobacillus plantarum were isolated from spontaneously fermented cereals made into “Ogi” and identified using classical methods. They were further characterized using molecular methods by polymerase chain reaction (PCR) amplification of 16S rDNA genes to confirm their identities. The genotypic characterization however showed that 85% of the organisms identified using conventional method as L. plantarum correlated, while 15% did not correlate; 2 were identified as Lactobacillus pentosus and one unidentified Lactobacillus sp. The method is a rapid and reliable way of producing a large number of copies of a specific DNA sequence for the identification of LAB. This method is however, able to solve the problem of poor identification that is usually associated with the identification of this fastidious organism that is regularly used as probiotics, starter culture and bio-preservatives in fermented foods that are consumed and in biotechnology because they are generally regarded as safe. Key words: Molecular methods, conventional, Lactobacillus plantarum identification, fermented foods, species and genera level, rapid, reliable.