UTILIZATION OF LACTIC ACID BACTERIA AND EXTRACELLULAR COMPOUNDS IN BIOLOGICAL CONTROL OF FUNGAL SPECIES PUBLISHEDS.MATEI(1) , A.MATEI(2), Gabi-Mirela MATEI(1), Călina Petruța CORNEA(2
Abstract: The goal of the present paper was to present the results of the research carried out for selecting efficient bacterial strains against fungal contaminants of vegetal products, to investigate the possibilities to use selected strains and their extracellular compounds in local control of pathogenic or spoilage fungi, as well as the interactions between lactic acid bacteria with antifungal effect and target fungi. Recent research attests the effect of lactic acid bacteria by producing antagonist compounds able to control pathogenic fungi (lactic, acetic, phenyl-lactic, cyclic dipeptides, reuterin, biosurfactants). Lactic acid bacteria selected from various plant materials or traditional Romanian foods were tested for their antagonistic effect on the mycotoxigenic fungal contaminants of fresh and processed fruits or vegetables. In vitro antagonistic activity of 9 lactic acid bacterial strains was assayed against 5 fungal isolates from genera Penicillium and Aspergillus by double layer method on solid media and by co-cultivation in liquid media. In vivo assay of antifungal effect of two efficient LAB strains as biocontrol agents for apple rot was carried out. Lactic acid bacteria strains LAB 13, LAB 15, LAB 43, LAB 58 presented highly effective antifungal activity, comparably to the reference strains Lpl and Lpa, against pathogenic and spoilage fungal isolates. Antifungal effect of the selected strains revealed by optical microscopy, evidenced structural damages of the hyphae, conidiophores and induced sporulation delays. Among lactic acid bacteria with antifungal activity, the strain LAB 58 presented the highest emulsification ability by releasing biosurfactants with anionic charge, with anti-biofilm effect. Wounded apples treated experimentally with strains LAB 58 and LAB13 and exposed to Penicillium expansum spore suspension developed smaller infection spots comparatively with non treated control. Data obtained from in vitro and in vivo assays were similar, confirming the reliability of results and the antifungal activity of LAB strains and their exometabolites, with the posibility to be utilized as biopreservatives for fruits.
Key words: lactic acid bacteria, pathogenic fungi, antagonistic effect, inhibition zone, biopreservation