The role of AI-2/LuxS system in biopreservation of fresh refrigerated shrimp: Enhancement in competitiveness of Lactiplantibacillus plantarum for nutrients.

Quorum sensing of lactic acid bacteria, mediated by the Autoinducer-2 (AI-2)/LuxS system, positively regulates antibacterial activity, which is an effective strategy for aquatic product preservation. This study revealed that AI-2/LuxS system regulates the nutritional competitiveness of LAB by facilitating membrane transport systems in preservation of vacuum-packaged refrigerated shrimp (VPRS), using Lactiplantibacillus plantarum SS-128 wild-type and the luxS mutant strain. In VPRS preservation, organisms that cause spoilage and total volatile basic nitrogen were significantly lower in the VPRS inoculated with L. plantarum SS-128 than those inoculated with the luxS mutant strain (L. plantarum ΔluxS/SS-128) (p < 0.05). Simulations in vitro using diluted shrimp juice showed the growth inhibitory effects of wild-type strain SS-128 on the main VPRS spoilage microorganism Shewanella baltica. This could potentially be attributed to more efficient nutrient utilization, presumably mediated by AI-2/LuxS system, as revealed by interaction analysis. In support of this, in vitro nutritional competition test showed that L. plantarum SS-128 was more competitive for nutrients when cocultured with S. baltica under conditions of limited nutrient availability. Subsequently, an integrated analysis of transcriptomic and metabolomic revealed that AI-2/LuxS enables a continuous expansion of L. plantarum SS-128 by balancing energy expenditure followed by enhancing membrane transport systems, which is the main driven forces for it to occupy a favourable niche quickly. Our results showed that the AI-2/LuxS system may regulate the nutritional competitiveness of lactic acid bacteria and may be a regulatory strategy for biological preservation of aquatic products.

How Do Trichoderma Genus Fungi Win a Nutritional Competition Battle against Soft Fruit Pathogens? A Report on Niche Overlap Nutritional Potentiates.

We present a case study report into nutritional competition between Trichoderma spp. isolated from wild raspberries and fungal phytopathogenic isolates (Colletotrichum sp., Botrytis sp., Verticillium sp. and Phytophthora sp.), which infect soft fruit ecological plantations. The competition was evaluated on the basis of nutritional potentiates. Namely, these were consumption and growth, calculated on the basis of substrate utilization located on Biolog® Filamentous Fungi (FF) plates. The niche size, total niche overlap and Trichoderma spp. competitiveness indices along with the occurrence of a stressful metabolic situation towards substrates highlighted the unfolding step-by-step approach. Therefore, the Trichoderma spp. and pathogen niche characteristics were provided. As a result, the substrates in the presence of which Trichoderma spp. nutritionally outcompete pathogens were denoted. These were adonitol, D-arabitol, i-erythritol, glycerol, D-mannitol and D-sorbitol. These substrates may serve as additives in biopreparations of Trichoderma spp. dedicated to plantations contaminated by phytopathogens of the genera Colletotrichum sp., Botrytis sp., Verticillium sp. and Phytophthora sp.