A STUDY OF LACTOBACILLUS PLANTARUM STRAINS ISOLATED FROM TABLE OLIVE FERMENTATION FOR THE PRESENCE OF GENES WITH TECHNOLOGICAL INTEREST AND THEIR EXPRESSION UNDER VARIOUS CONDITIONS

摘要

A total of 16 Lactobacillus plantarum strains (isolates from fermented olives) were studied for the presence and expression of genes that belong to pin loci and are known for their involvement to the production of bacteriocins, pheromones (substances enabling bacterial growth) as well as other peptides. The presence of 13 genes that belong to pin loci were monitored with the polymerase chain reaction (PCR), while for the study of gene expression, the strains were cultured in growth medium with a variant salinity (0, 4, 6 and 8% NaCl) and pH (3.5, 4.0, 4.5, and 6.4). The filtered sterile supernatant of the bacterial cultures (8 log cfu/mL) was tested with an agar well diffusion assay; the growth medium had been previously inoculated with different non pathogen (15 Lb. pentosus) and pathogen strains (5 Escherichia coli, 6 Listeria monocytogenes, 10 Salmonella enterica, 3 Staphylococcus aureus). The growth of six Lb. plantarum strains on the medium (0% NaCl, pH 6.4) (control) was found to be able to produce bacteriocins against Lb. pentosus. From the aforementioned strains, 3 and 2 were found to inhibit the growth of Lb. pentosus when the strains cultured on the growth medium supplemented with 4% and 6% NaCI (pH 6.4) respectively. Additionally, the inhibition was greater in two cases of culture on 4% NaCI in comparison with the control. On the contrary, growth of Lb. pentosus strains was favoured when the Lb. plantarum strains cultured on a growth medium with a variant pH (3.5, 4.0, and 4.5). In some cases, the growth of the strains on medium supplemented with 6% NaCI was found to be able to enhance the production of pheromones. Similar results have been obtained during the growth on the medium supplemented with 8% NaCI (pH 6.4). Furthermore, inhibition of the pathogens was not observed. The inhibition was found to be affected by the level of salinity on the growth medium and the different Lb. pentosus strains. On the other hand, the production of pheromones seemed to be associated with the development in an acidic environment. These results reveal that further studies are needed for the correlation of the production of pheromones and bacteriocins in different growth conditions, as well as for the possibility of gene expression in the cases that seemed not to be expressed. In accordance, it will be useful to find the combination of the conditions leading to the expression of bacteriocins which will be able to inhibit pathogenic bacteria.