Comparative transcriptomic analysis of Lactiplantibacillus plantarum RS66CD biofilm in high-salt conditions and planktonic cells

Research progress on the regulatory mechanism of biofilm formation in probiotic lactic acid bacteria

Probiotic lactic acid bacteria (LAB) must undergo three key stages of testing, including food processing, storage, and gastrointestinal tract environment, their beneficial effects could exert. The biofilm formation of probiotic LAB is helpful for improving their stress resistances, survival rates, and colonization abilities under adverse environmental conditions, laying an important foundation for their probiotic effects. In this review, the formation process, the composition and function of basic components of probiotic LAB biofilm have been summarized. This review focuses on the regulatory mechanism of probiotic LAB biofilm formation. In addition, the characteristics and related mechanisms of probiotics in biofilm state have been analyzed to guide the application of probiotic LAB biofilms in the field of health and food. The biofilm formation of LAB is an extremely complex process involving multiple regulatory factors. Besides quorum sensing (QS), other regulatory factors are not yet fully understood. The probiotic LAB in biofilm state exhibit superior survival rate, adhesion performance, and immunomodulation ability, attribute to various metabolic processes, including stress response, exopolysaccharide (EPS) metabolism, amino acid and protein metabolisms, etc. The understanding about regulatory mechanism of biofilm formation of different probiotic species and strains will accelerate the development and application of probiotics products.

Understanding the transcriptomic response of Lactiplantibacillus pentosus LPG1 during Spanish-style green table olive fermentations

Lactiplantibacillus pentosus (Lbp. pentosus) is a species of lactic acid bacteria with a great relevance during the table olive fermentation process, with ability to form non-pathogenic biofilms on olive epidermis. The objective of this work is to deepen into the genetic mechanisms of adaptation of Lpb. pentosus LPG1 during Spanish-style green table olive fermentations, as well as to obtain a better understanding of the mechanisms of adherence of this species to the fruit surface. For this purpose, we have carried out a transcriptomic analysis of the differential gene expression of this bacterium during 60 days of fermentation in both brine and biofilms ecosystems. In brines, it was noticed that a total of 235 genes from Lpb. pentosus LPG1 were differentially expressed during course of fermentation and grouped into 9 clusters according to time-course analysis. Transport and metabolism of carbohydrates and amino acids, energy production, lactic acid and exopolysaccharide synthesis genes increased their expression in the planktonic cells during course of fermentation. On the other hand, expression of genes associated to stress response, bacteriocin synthesis and membrane protein decreased. A total of 127 genes showed significant differential expression between Lpb. pentosus LPG1 planktonic (brine) and sessile (biofilms) cells at the end of fermentation process (60 days). Among the 64 upregulated genes in biofilms, we found genes involved in adhesion (strA), exopolysaccharide production (ywqD, ywqE, and wbnH), cell shape and elongation (MreB), and well as prophage excision. Deeping into the genetic bases of beneficial biofilm formation by Lpb. pentosus strains with probiotic potential will help to turn this fermented vegetable into a carrier of beneficial microorganisms to the final consumers.

Deciphering the antibiofilm potential of 2-Phenylethyl methyl ether (PEME), a bioactive compound of Kewda essential oil against Staphylococcus aureus

Opportunistic pathogenic bacteria and their pathogenicity linked with biofilm infections become a severe issue as they resist the actions of multiple antimicrobial drugs. Naturally derived drugs having antibiofilm properties are more effective than chemically synthesized drugs. The plant derived essential oils are a rich source of phytoconstituents with widespread pharmacological values. In the present investigation, a major phytoconstituent, 2-Phenyl Ethyl Methyl Ether (PEME) of Kewda essential oil extracted from the flowers of Pandanus odorifer was explored for its prospective antimicrobial and anti-biofilm properties against ESKAPE pathogenic bacterial strain, Staphylococcus aureus and MTCC 740. The minimum inhibitory concentration (MIC) of PEME was found to be 50 mM against the tested bacterial strains. A gradual decrease in biofilm production was observed when PEME was treated with the sub-MIC concentration. The reduction in biofilm formation was noticeable from qualitative assay i.e., Congo Red Agar Assay (CRA) and further quantified by crystal violet staining assay. The decline in exopolysaccharides production was quantified, with the highest inhibition against MTCC 740 with a decrease of 71.76 ± 4.56% compared to untreated control. From the microscopic analysis (light and microscopic fluorescence method), PEME exhibited inhibitory effect on biofilm formation on the polystyrene surface. The In silico studies stated that PEME could invariably bind to biofilm associated target proteins. Further, transcriptomic data analysis suggested the role of PEME in the down-regulation of specific genes, agrA, sarA, norA and mepR, which are critically associated with bacterial virulence, biofilm dynamics and drug resistance patterns in S. aureus. Further, qRT-PCR analysis validated the role of PEME on biofilm inhibition by relative downregulation of agrA, sarA, norA and mepR genes. Further, advanced in silico methodologies could be employed in future investigations to validate its candidature as promising anti-biofilm agent.

Deep Shotgun metagenomic and 16S rRNA analysis revealed the microbial diversity of lactic acid bacteria in traditional fermented foods of eastern Hainan, China

The eastern part of Hainan, China, has a flat terrain and a suitable climate with abundant sunshine and rain. This unique environment makes the tropical microbial resources of natural fermented food unique and rich. Therefore, we combined Shotgun metagenomic sequencing, 16S rRNA sequencing and pure culture technology to analyze the microbial diversity, microbiota composition, species differences and correlation of 30 traditional fermented food samples collected from Wenchang, Qionghai, Wanning and Lingshui in the eastern part of Hainan province, and isolated, identified and preserved the microorganisms in them. The results showed that the microbial community structure differs significantly between samples from different regions and between different substrates. The alpha diversity of microorganisms in traditional fermented foods in the Wanning area was higher than those of the other three areas. The beta diversity indicated that the microbiota structural difference between Wanning and Qionghai was smaller. This is consistent with the fact that the precipitation in the Wanning area is the highest and similar to that of Qionghai. The alpha diversity of microorganisms was the highest in fermented vegetables, followed by fermented grains, and the lowest in fermented seafood. Beta diversity showed that the microbiota composition of fermented grains and fermented vegetables is very similar, but that of fermented seafood is significantly different. The results of microbiota structural analysis showed that firmicutes and proteobacteria are the dominant bacterial phyla, and Lactobacillus plantarum and Lactobacillus fermentum are the dominant species in traditional fermented foods in eastern Hainan. Lactic acid bacteria are the dominant species in traditional fermented foods from the eastern Hainan region of China, regardless of the substrate used in fermentation. According to the microbial functional characteristics, the microbial metabolism and biosynthesis pathways in traditional fermented foods in Hainan tend to be active. In addition, combined with pure culture technology, we isolated, identified and preserved 342 lactic acid bacteria strains from traditional fermented food in eastern Hainan province. This study helped us understand the different characteristics of microbial communities in tropical southern China and supplement the Lactobacillus species resource pool in tropical southern China. Moreover, it provided new insights and directions for the development and utilization of fermented foods.

Biofilm characteristics and transcriptomic profiling of Acinetobacter johnsonii defines signatures for planktonic and biofilm cells

Most bacteria in the natural environment have a biofilm mode of life, which is intrinsically tolerant to antibiotics. While until now, the knowledge of biofilm formation by Acinetobacter johnsonii is not well understood. In this study, the characteristics and the effect of a sub-inhibitory concentration of antibiotic on A. johnsonii biofilm and planktonic cells were determined. We discovered a positive relationship between biofilm formation and tetracycline resistance, and biofilms rapidly evolve resistance to tetracycline they are treated with. Persister cells commonly exist in both planktonic and biofilm cells, with a higher frequency in the latter. Further transcriptomic analysis speculates that the overexpression of multidrug resistance genes and stress genes were mainly answered to sub lethal concentration of tetracycline in planktonic cells, and the lower metabolic levels after biofilm formation result in high resistance level of biofilm cells to tetracycline. Altogether, these data suggest that A. johnsonii can adjust its phenotype when grown as biofilm and change its metabolism under antibiotic stress, and provide implications for subsequent biofilm control.

Comparative Transcriptome Analysis of Shewanella putrefaciens WS13 Biofilms Under Cold Stress

Shewanella putrefaciens is a Gram-negative bacterium that can cause seafood spoilage under low-temperature conditions. The bacterium easily forms biofilms to enhance its survival in challenging environments. Our previous research revealed that the biofilm formed by S. putrefaciens WS13 under the low temperature (4 °C) has larger biomass and tighter structure than at an optimum growth temperature (30 °C). In this study, comparative transcriptome analysis was further performed to get insights into the global-level of gene expression in the biofilm formed by S. putrefaciens WS13 under the refrigerating and optimal temperatures using Illumina RNA-Sequencing technique. The results revealed that a total of 761 genes were differentially expressed, of which 497 were significantly up-regulated and 264 were significantly down-regulated (p<0.05). The qRT-PCR results of randomly selected differentially expressed genes (DEGs) confirmed the RNA sequencing results. Comparison of transcriptome data revealed 28 significantly changed metabolic pathways under the cold stress, including the down-regulated chemotaxis, and motility, and up-regulated tryptophan metabolism, histidine biosynthesis, and quorum sensing, which benefited the biofilm formation of S. putrefaciens WS13 under the adverse circumstance. This study provided useful data for better understanding of the biofilm formation of S. putrefaciens, and also laid a theoretical foundation for novel vaccine and drug targets against the severe spoilage bacterium under the cold stress.