Studies On Antifungal Properties And Comparative Genomics Of Lactobacillus Plantarum

Lactobacillus（L.）plantarum,regarded as generally recognized as safe,having antifungal attributes,can be used in food processing and production in place of chemical preservatives.Which can substantially reduce the risk of fungal contamination,improve quality,safety and shelf-life of the final product.To date,the research on the antifungal properties of L.plantarum has mainly focused on the physiological and biochemical characteristics.Moreover,it was difficult to elucidate the existence of strain specificity in the antifungal activity,which also limited the development and utilization of antifungal L.plantarum strains.In this study,122 isolates of L.plantarum were screened based on inhibitory activity against six common spoilage fungi and the tolerance against acid and bile salt.And LC-MS technology was used to identify the antifungal substances,potential L.plantarum candidates with antifungal activity were applied in food preservation.At the same time,Illumina MiSeq sequencing platform was used to re-sequence the whole genome of 122 L.plantarum isolates,having different antifungal activities.The genome data set of 551 L.plantarum was constructed by using NCBI.Base on the analysis of their genetic background,evolution process and functional genes,the evolution theory of L.plantarum group was supplemented,and the molecular mechanism of different antibacterial characteristics was revealed.The main results and conclusions are as follows:（1）L.plantarum IMAU80174,among 122 isolates,was selected as the most effective strain,based on the results of antifungal activity against six common food spoilage fungi and tolerance against acid and bile salts.The major antifungal compounds of the cell free supernatant（CFS）of L.plantarum IMAU80174 were lactic acid（3.35 g/L）and acetic acid（0.88 g/L）.Moreover,propionic,phenyllactic,4-hydroxyphenyllactic acid,bacillin and diacetyl possibly had synergistic effect at low concentrations.（2）Application of L.plantarum and its CFS possibly effectively decreased the rate of decay and lesion in fruit and bread,subject to inoculation with the spoilage fungus Penicillium expansum and Aspergillus flavus.（3）Pan-genome analysis of 551 L.plantarum strains contained 57132 genes,and the core genome included 661 genes,accounting for only 1.16%.It could be implied that L.plantarum had a high genetic diversity.（4）Phylogenic tree was constructed by using a strict core-genome of L.plantarum,followed by refining the five clades/subclades with genome-wide single nucleotide polymorphisms（SNPs）.Our data showed that plant-originated isolates were evenly dispersed across the phylogenetic tree,which corroborated a previously reported model of nomadic lifestyle.Isolates from animal and dairy sources showed significant biasedness in clade distribution,suggesting close association between bacterial genomes and habitats.Both animal and dairy sources were directly linked with the development of human civilization in the aspects of food culture and food industry.（5）Combined with the phenotypic characteristics of antifungal activity of 122 L.plantarum isolates,genome-wide association study was performed.And a SNP site（Chr₂030723）was identified which was significantly associated with the antifungal property of the isolates.This site was in the coding gene of holin.In conclusion,L.plantarum IMAU80174 has broad-spectrum antifungal activity and has high application potential as a bio-preservative.Based on many accessible and newly sequenced genomes,this work,for the first time,identified previously unfound association between genomic profiles and niches.Particularly,the dairy-and animal-originated strains presented habitat-specific genomic features which provides new insights into the survival mechanism of this species in various niches.The mapping of key factors of antifungal activity of L.plantarum by genome-wide association analysis can be used as a reference index for rapid screening of antifungal L.plantarum strains.