Improving 3-phenyllactic acid production of Lactobacillus plantarum AB-1 by enhancing its quorum-sensing capacity.

3-Phenyllactic acid (PLA) is a novel and natural antimicrobial compound. However, the concentration of PLA produced by native microbes was rather low. To enhance the production of PLA of Lactobacillus plantarum AB-1, the microcapsules of L. plantarum AB-1 cells with a high quorum-sensing capacity was established and investigated. In addition, the relation between PLA production and quorum sensing was further investigated and confirmed by adding the exogenous 4,5-dihydroxy-2,3-pentanedione (DPD, AI-2 precursor). The results indicated that the PLA production of L. plantarum AB-1 in microencapsulated cells (MC cells) was higher than that of the free cells, and the lactate dehydrogenase activity, autoinducer-2 (AI-2) levels and the relative expression of the luxS gene were also significantly increased in MC cells (P < 0.05). In addition, the cell growth, AI-2 levels and PLA production of L. plantarum AB-1 were also significantly promoted after adding 24 µM exogenous DPD. The results suggest that the PLA production of L. plantarum was partly regulated by the AI-2/LuxS system, and microencapsulation can increase the local AI-2 level and enhance QS capacity, which are beneficial to PLA production. The results may provide a new insight and experimental basis for the industrial production of PLA.

AHLs-produced bacteria in refrigerated shrimp enhanced the growth and spoilage ability of Shewanella baltica.

Shewanella baltica is the predominant bacteria in spoiled shrimp (Litopenaeus vannamei), however, the spoilage ability and the mechanism of S. baltica is still unknown. S. baltica can't produce the signal molecule of acyl-homoserine-lactones (AHLs), so the aim of this study was to investigate how wild type S. baltica SA03 (WT SA03) eavesdrop exogenous AHLs to enhance its spoilage ability through LuxR receptor. The results indicated that Aeromonas spp. (Aer), Acinetobacter spp. (Aci) and Serratia spp. (Ser) isolated from refrigerated shrimp can produce different AHLs. WT SA03 can eavesdrop the AHLs of Aer (C4-HSL), Aci (O-C6-HSL) and Ser (C6-HSL, O-C6-HSL) to enhance its growth, especially Ser. Exogenous C4-HSL and C6-HSL enhanced biofilm formation of WT SA03, and C6-HSL and O-C6-HSL enhanced thioredoxin reductase trxB mRNA expression. However, the luxR mutant of WT SA03 (ΔluxR SA03) lost or weakened the role of using environmental AHLs. In vivo experiments, the lag time of WT SA03 was shortened by 6.4 h, 6.2 h and 14.4 h by co-inoculated with Aer, Aci and Ser, respectively. The total volatile basic nitrogen (TVB-N) were significantly enhanced in the samples co-inoculated with WT SA03 and Aer (or Aci, Ser) than those of ΔluxR SA03 and Aer (or Aci, Ser) (p < 0.05). The results showed that S. baltica SA03 can utilize AHLs produced by other bacteria to enhance its growth and spoilage ability through LuxR receptor system. Quorum sensing based on AHLs of bacteria might as the potential targets for food spoilage control.

Cooperation of lactic acid bacteria regulated by the AI-2/LuxS system involve in the biopreservation of refrigerated shrimp.

Litopenaeus vannamei is an extremely perishable food because of rapid microbial growth and chemical degradation after harvesting. Biopreservation is a food preservation technology based on the addition of "positive" bacteria to kill or prevent the growth of undesirable microorganisms. In this study, the cooperation between lactic acid bacteria (LAB) strains (Lactobacillus plantarum AB-1 and Lactobacillus casei) regulated by the AI-2/LuxS was investigated in vitro and on shrimp. The antimicrobial activity of L. plantarum AB-1 was significantly increased in the co-culture compared with the mono-culture in vitro, and the transcription of the quorum sensing luxS gene and bacteriocin regulatory operons (plnB and plnC) in L. plantarum AB-1 were also significantly increased in co-culture (P < .05), indicating cooperation and that the production of bacteriocin in L. plantarum AB-1 might be related to the LuxS/AI-2 quorum sensing (QS) system. The results were confirmed by adding the exogenous AI-2 molecule signal to L. plantarum AB-1 in vitro. In the on shrimp experiments, the spoilage organisms (mainly Shewanella baltica) in shrimp samples were significantly inhibited after co-inoculation with L. plantarum AB-1 and L. casei, and the values of total volatile basic nitrogen (TVB-N) and pH in co-inoculated shrimp were also significantly decreased (P < .05). In addition, the AI-2 activities in co-inoculated shrimp were significantly higher during refrigerated storage. The results suggest that the cooperation and bacteriocin production of lactic acid bacteria might by regulated by the AI-2/LuxS system, and the co-inoculation of L. plantarum AB-1 and L. casei in shrimp is an effective strategy for biopreservation of shrimp.

Colquhounia Root Tablet Protects Rat Pulmonary Microvascular Endothelial Cells against TNF-α-Induced Injury by Upregulating the Expression of Tight Junction Proteins Claudin-5 and ZO-1.

BACKGROUND: There are currently limited effective pharmacotherapy agents for acute lung injury (ALI). Inflammatory response in the lungs is the main pathophysiological process of ALI. Our preliminary data have shown that colquhounia root tablet (CRT), a natural herbal medicine, alleviates the pulmonary inflammatory responses and edema in a rat model with oleic acid-induced ALI. However, the potential molecular action mechanisms underlining its protective effects against ALI are poorly understood. This study aimed to investigate the effects and mechanism of CRT in rat pulmonary microvascular endothelial cells (PMEC) with TNF-α-induced injury. METHODS: PMECs were divided into 6 groups: normal control, TNF-α (10 ng/mL TNF-α), Dex (1×10-6 M Dex + 10 ng/mL TNF-α), CRT high (1000 ng/mL CRT + 10 ng/mL TNF-α), CRT medium (500 ng/mL CRT + 10 ng/mL TNF-α), and CRT low group (250 ng/mL CRT + 10 ng/mL TNF-α). Cell proliferation and apoptosis were detected by MTT assay and flow cytometry. Cell micromorphology was observed under transmission electron microscope. The localization and expression of tight junction proteins Claudin-5 and ZO-1 were analyzed by immunofluorescence staining and Western blot, respectively. RESULTS: TNF-a had successfully induced an acute endothelial cell injury model. Dex and CRT treatments had significantly stimulated the growth and reduced the apoptosis of PMECs (all p < 0.05 or 0.01) and alleviated the TNF-α-induced cell injury. The expression of Claudin-5 and ZO-1 in Dex and all 3 CRT groups was markedly increased compared with TNF-a group (all p < 0.05 or 0.01). CONCLUSION: CRT effectively protects PMECs from TNF-α-induced injury, which might be mediated via stabilizing the structure of tight junction. CRT might be a promising, effective, and safe therapeutic agent for the treatment of ALI.