N-acyl-homoserine lactone produced by Rahnella inusitata isolated from the gut of Galleria mellonella influences Salmonella phenotypes.

The most studied mechanism of quorum sensing in Gram-negative bacteria is mediated by autoinducer 1 (AI-1), namely, acyl-homoserine lactone (AHL). This system allows communication among different bacterial species and regulates the expression of virulence genes in many pathogens. Although AHL-producing bacteria have been detected in the intestines of humans and other animals, no report was found about AHL-producing bacteria in the insect gut and the possible effects of these autoinducers on enteropathogenic bacteria. Therefore, this study aimed to identify AHL-producing bacteria in the gut of larvae of Galleria mellonella and to evaluate the influence of this quorum sensing signal on the regulation of adhesion and motility phenotypes in the intestinal pathogen Salmonella. Sequencing of the 16S rRNA gene, 16S rRNA gene-based phylogenetic analyses, and phenotypic characterization of gut isolates was performed. The profile of AHLs produced by the isolates was determined using thin-layer chromatography (TLC) and revealed with the biosensor strain Chromobacterium violaceum CV026. Sequencing, phylogenetic analyses and phenotypic characterization of gut isolates showed that the three AHL-producing strains belong to the species Rahnella inusitata, named GM34, GM56, and GM60. The TLC showed that R. inusitata produces a six-carbon AHL. In the presence of cell-free extract of R. inusitata containing AHL and under anaerobic conditions, Salmonella enterica increased the adhesion to stainless steel coupons and presented swarming motility. Extracts from the culture medium of R. inusitata isolates containing AHL increased the adhesion on stainless steel coupons and swarming motility of Salmonella enterica serovar Enteritidis PT4 under anaerobic conditions. The results suggest the possibility of communication between members of the G. mellonella intestinal microbiota with pathogens such as Salmonella.

Antarctic Rahnella inusitata: A Producer of Cold-Stable ß-Galactosidase Enzymes.

There has been a recent increase in the exploration of cold-active ß-galactosidases, as it offers new alternatives for the dairy industry, mainly in response to the current needs of lactose-intolerant consumers. Since extremophilic microbial compounds might have unique physical and chemical properties, this research aimed to study the capacity of Antarctic bacterial strains to produce cold-active ß-galactosidases. A screening revealed 81 out of 304 strains with ß-galactosidase activity. The strain Se8.10.12 showed the highest enzymatic activity. Morphological, biochemical, and molecular characterization based on whole-genome sequencing confirmed it as the first Rahnella inusitata isolate from the Antarctic, which retained 41-62% of its ß-galactosidase activity in the cold (4 °C-15 °C). Three ß-galactosidases genes were found in the R. inusitata genome, which belong to the glycoside hydrolase families GH2 (LacZ and EbgA) and GH42 (BglY). Based on molecular docking, some of these enzymes exhibited higher lactose predicted affinity than the commercial control enzyme from Aspergillus oryzae. Hence, this work reports a new Rahnella inusitata strain from the Antarctic continent as a prominent cold-active ß-galactosidase producer.

Co-transmission of Rahnella aquatilis between hospitalized patients.

Rahnella aquatilis is an environmental Gram-negative bacillus that is rarely reported as human pathogen, being mainly associated with infections in immunocompromised patients. Herein we describe two cases of R. aquatilis isolates recovered from endotracheal aspirate cultures of different patients in a tertiary hospital located in the city of São Paulo, Brazil. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 16S rDNA gene sequencing were performed to confirm bacterial identification after the isolates being erroneously identified as Pantoea spp. by automated system. Both isolates showed the same PFGE pattern and presented the ß-lactamase encoding gene blaRAHN-1, responsible for resistance to cephalothin. The isolates were susceptible to broad-spectrum cephalosporins, carbapenems, fluoroquinolones, aminoglycosides, and polymyxin B. This report shows the presence and transmission of uncommon bacteria in the nosocomial environment and alerts us about the need for new tools of correct microbiologic diagnosis.

Freezing and freeze-drying of the bacterium Rahnella aquatilis BNM 0523: study of protecting agents, rehydration media and freezing temperatures.

AIMS: The aim of the present study was to evaluate and compare freezing and freeze-drying treatments for conserving Rahnella aquatilis (BNM 0523) with the goal to achieve an adequate commercial formulation of this biocontrol agent. METHODS AND RESULTS: The effect of several protective agents, rehydration media and freezing temperatures on the viability and functional activity of the R. aquatilis was investigated. The storage stability at 3 months and 4 years was determined by checking the viability of the cells and their biocontrol capability against Botrytis cinerea by measuring the percentage of reduction of disease severity on apple. The best results were obtained by the freeze-drying of the cells using a mixture of skimmed nonfat milk 10%, yeast extract 0·5% and glucose 1% as the protecting and rehydrating medium, and a quickly freezing (-70°C) before the freeze-drying. In this case, the viability of the cells after 4 years was 98%, and their antagonistic ability showed a little decrease with respect fresh cells. CONCLUSIONS: The studies showed that R. aquatilis was resistant to freezing and freeze-drying when it was used a mixture of cryoprotectants and that it was possible to obtain inoculums with high viability and good effectiveness for reduction of decay caused by B. cinerea. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is probably the first report about the resistance of R. aquatilis to freezing and freeze-drying treatments and shows that these operations could be useful for obtaining a commercial formulation of this biocontrol agent.

Biological control of postharvest spoilage caused by Penicillium expansum and Botrytis cinerea in apple by using the bacterium Rahnella aquatilis.

The epiphytic bacterium Rahnella aquatilis, isolated from fruit and leaves of apples, was tested for antagonistic properties against Penicillium expansum and Botrytis cinerea on Red Delicious apple fruit. In "in vitro" assays, this bacterium inhibited completely the germination of P. expansum and B. cinerea spores, but it needed direct contact with the spores to do it. However the putative mechanism seemed be different for the two pathogens. The bacterium did not produce extracellular antibiotic substances and when the acute toxicity test was performed no mortality, toxicity symptoms or organ alterations of the test animals (Wistar rats) were observed. Assays of biological control of P. expansum and B. cinerea on apple fruit were carried out at different temperatures. At 15 degrees C and 90% RH, the incidence of disease caused by P. expansum on apples stored for 20 days, was reduced by nearly 100% by R. aquatilis (10(6) cells/ml), while in the case of B. cinerea, the reduction of decay severity was nearly 64% but there was no reduction in the incidence of disease. At 4 degrees C and 90% RH the treatment with the bacterium significantly inhibited the development of B. cinerea on apples stored for 40 days and the incidence of disease was reduced by nearly 100%, while the incidence of disease caused by P. expansum at 4 degrees C was 60%. The results obtained show that R. aquatilis would be an interesting microorganism to be used as a biocontrol agent.

Primeras identificaciones de Rahnella aquatilis en Costa Rica / Firts identification of Rahnella aquatilis in Costa Rica

Se reporta el aislamiento de Rahnella aquatilis en dos pacientes, en muestras de secreción umbilical con fístula entero cutánea y orina de infección urinaria obtenida por punción vesical. Se mencionan las características bioquímicas que permiten su clasificación, así como su comportamiento ante los antimicrobianos. Se reporta que ambos casos se resolvieron exitosamente. Se hace revisión de la literatura al respecto y se señala la baja frecuencia de aislamiento de esta bacteria, en el campo clínico, a nivel mundial