The annotation of full genomes of amylolytic lactic acid bacteria (ALAB) leads to conviction that many of them contain a basic pool of chromosomal genes, responsible for starch hydrolysis. However, only the strains that are forced to survive in starchy environment are able to display these genetically determined properties. The aim of the present work is to investigate the genes actually engaged in starch utilization by ALAB using gene transcription assay. Twenty five new ALAB strains, belonging to 11 distinct species of four genera were isolated and analyzed. Among them, the first amylolytic Lactobacillus sakei, Enterococcus faecium, and E. durans were reported. The presence and expression of the genes amy1, glgP, glgB, agl, malL, treC, and dexC were examined. Although all strains possessed extracellular and cell-bound amylase activity and produced lactic acid from starch, high genus and species specificity in the gene expression was observed. ALAB strains of genus Lactobacillus (except L. sakei) and P. acidilactici own and express all the tested genes, while E. faecium and E. durans strains expressed predominantly the gene, encoding amylase. The co-transcription of glgP and glgB genes indicates that glycogen synthesis and starch degradation occur in parallel, which is another example for dual metabolic role of biochemical paths.

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Lactobacillus paracasei DSM 23505 is able to produce high amounts of lactic acid (LA) by simultaneous saccharification and fermentation (SSF) of inulin. Aiming to obtain the highest possible amounts of LA and fructose, the present study is devoted to evaluate the impact of bivalent metal ions on the process of inulin conversion. It was shown that Mn strongly increases the activity of the purified key enzyme β-fructosidase. In vivo, batch fermentation kinetics revealed that the high Mn concentrations accelerated inulin hydrolysis by raise of the inulinase activity, and increased sugars conversion to LA through enhancement of the whole glycolytic flux. The highest LA concentration and yield were reached by addition of 15 mM Mn-151 g/L (corresponding to 40% increase) and 0.83 g/g, respectively. However, the relative quantification by real-time reverse transcription assay showed that the presence of Mn decreases the expression levels of fosE gene encoding β-fructosidase. Contrariwise, the full exclusion of metal ions resulted in fosE gene expression enhancement, blocked fructose transport, and hindered fructose conversion thus leading to huge fructose accumulation. During fed-batch with optimized medium and fermentation parameters, the fructose content reached 35.9% (w/v), achieving yield of 467 g fructose from 675 g inulin containing chicory flour powder (0.69 g/g). LA received in course of the batch fermentation and fructose gained by the fed-batch are the highest amounts ever obtained from inulin, thus disclosing the key role of Mn as a powerful tool to guide inulin conversion to targeted bio-chemicals.