Maksim Nikolaevich Sokolov

Bacterial density-dependent intercellular communication systems known as Quorum Sensing (QS) play a key role in regulating numerous physiological processes that determine the interactions of microorganisms with their hosts and environment. Ways of suppressing QS, or Quorum Quenching (QQ), are considered a promising approach for controlling pathogenicity and other undesirable bacterial traits, stimulating an active search for new QS inhibitors. One of the best-studied QQ mechanisms to date is the enzymatic hydrolysis of autoinducers—N-acyl-homoserine lactones (AHLs). This review systematizes data on the potential sources of QQ enzymes and discusses their main classes and specificity of action. The ecological significance of QQ mechanisms is discussed. Various approaches to the use of QQ enzymes in medicine, industry, and agriculture are analyzed.

Orchid plants, due to their high aesthetic qualities of large inflorescences, long flowering period, and ease of care, have high commercial potential; however, when grown industrially in factories, they are susceptible to infectious diseases. In this study, we isolated from Phalaenopsis spp. plants epiphytic, rhizospheric, and endophytic bacteria associated with soft rot symptoms. Twenty-nine isolates exhibiting pectolytic activity were identified as strains of the genera Bacillus, Klebsiella, Microbacterium, Paenibacillus, Paracidovorax, Pseudomonas, and Psychrobacillus based on 16S rRNA analysis. These isolates were tested for their ability to produce cellulase, amylase, sucrase, proteinase, and lipase; to form biofilms; and to exhibit motility (swimming and swarming). Potato microplants under in vitro conditions were used as a model object for initial screening of the strains’ potential phytotoxicity. Most strains were shown to inhibit plant growth, particularly root development. Injection of suspensions of these strains into orchid leaves caused symptoms of soft rot. Thus, we isolated Gram-positive bacteria for the first time from orchid tissues with soft rot symptoms and demonstrated an association of these strains with plant tissue maceration in potato and orchids. Gram-positive bacteria with pectolytic activity are not typical pathogens of orchid soft rot and may require changes in approaches to the monitoring of phytopathogens for this group of plants.

Quorum Quenching (QQ) is a mechanism that disrupts Quorum Sensing (QS) signaling systems, which regulate gene expression based on bacterial population density. Many fish pathogens, such as Aeromonas, utilize QS systems to regulate the expression of their virulence factors. Disrupting these systems using QQ is a promising approach for infection control in aquaculture and may provide a safe alternative to antibiotics. Therefore, identifying microorganisms with QQ activity is a relevant task in agricultural microbiology and veterinary medicine. This study examines the identification of isolates with QQ activity in the microbial community of perch and assesses their probiotic potential for the prevention of aeromonosis. In this study, we isolated 32 strains of microorganisms capable of degrading N-acylhomoserine lactone (AHL), six of which exhibited stable QQ activity. Five strains were found to belong to the genus Rhodococcus, and one strain to the genus Exiguobacterium. The selected strains were tested for the enzymatic/non-enzymatic and intra-/extracellular QQ activity, pathogen growth inhibition, biofilm formation, and hemolytic activity, as well as growth ability under various environmental conditions (salinity, pH, bile acids, and temperature). Based on the results of these tests, the R. erythropolis PFS1.20 strain was selected as the most promising probiotic. The genomic analysis revealed that the studied strain contains genes encoding QQ enzymes, siderophore biosynthesis clusters, osmoprotectors, and compounds with antimicrobial properties. These results indicate the high probiotic potential of the R. erythropolis PFS1.20.