Mariana Piuri

The mechanisms underlying the health benefits of probiotics remain incompletely understood. Among the proposed mediators, bacterial extracellular vesicles (EVs) have been proposed as mediators of interkingdom communication between probiotic bacteria and their hosts. In this study, we show that Lacticaseibacillus casei BL23 releases higher EV levels during late stationary phase, with a predominant population of ∼113 nm. Scanning electron microscopy (SEM) confirmed the ultrastructural morphology of the EV preparations. Proteomic analysis revealed enrichment of proteins associated with probiotic function, including P40 and P75, as well as adhesion‐related moonlighting proteins such as glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) and enolase implicated in interactions with intestinal mucus and epithelial cells. L. casei BL23–derived EVs showed dose‐dependent interactions with mucin and with differentiated Caco‐2 epithelial monolayers in vitro. Using Transwell systems, we further demonstrated that intact EVs cross these polarized monolayers within 240 min. Super‐resolution microscopy further revealed time‐dependent uptake and intracellular trafficking of fluorescently‐labeled EVs. Together, these findings, obtained in vitro, are consistent with a role for probiotic‐derived EVs as postbiotics capable of mediating microbiota–host interactions at the intestinal barrier, providing the experimental basis for future validation in more complex physiological models.

Carbohydrate binding modules (CBMs) are protein domains that typically reside near catalytic domains, increasing substrate-protein proximity by constraining the conformational space of carbohydrates. Due to the flexibility and variability of glycans, the molecular details of how these protein regions recognize their target molecules are not always fully understood. Computational methods, including molecular docking and molecular dynamics simulations, have been employed to investigate lectin-carbohydrate interactions. In this study, we introduce a novel approach that integrates multiple computational techniques to identify the critical amino acids involved in the interaction between a CBM located at the tip of bacteriophage J-1’s tail and its carbohydrate counterparts. Our results highlight three amino acids that play a significant role in binding, a finding we confirmed through in vitro experiments. By presenting this approach, we offer an intriguing alternative for pinpointing amino acids that contribute to protein-sugar interactions, leading to a more thorough comprehension of the molecular determinants of protein-carbohydrate interactions.

Carbohydrate-binding modules (CBMs) are protein domains that typically reside near catalytic domains, increasing substrate-protein proximity by constraining the conformational space of carbohydrates. Due to the flexibility and variability of glycans, the molecular details of how these protein regions recognize their target molecules are not always fully understood. Computational methods, including molecular docking and molecular dynamics simulations, have been employed to investigate lectin-carbohydrate interactions. In this study, we introduce a novel approach that integrates multiple computational techniques to identify the critical amino acids involved in the interaction between a CBM located at the tip of bacteriophage J-1’s tail and its carbohydrate counterparts. Our results highlight three amino acids that play a significant role in binding, which we confirmed through in vitro experiments. By presenting this approach, we offer an intriguing alternative for pinpointing amino acids that contribute to protein-sugar interactions, leading to a more thorough comprehension of the molecular determinants of lectin-carbohydrate interactions.

Between 2015 and 2019, we hosted an International Phage Course at Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina. The 2-week full-time course was hands-on and included lectures from renowned phage biologists. Participating students were able to meet and discuss with recognized experts from around the world in a familiar setting, facilitating the establishment of scientific collaborations and the expansion of their networks. Eighty-four students from 14 Latin American countries have participated in the course, which included isolation, characterization, genome sequencing, and annotation of novel phages. We have successfully created a coursework that enabled the acquisition of new knowledge and expertise in bacteriophage biology and strengthened ties among Latin American colleagues.

Introduction: Because of the clinical relevance of Mycobacteria , and from a therapeutic perspective, there is an increasing interest to study phages that infect bacteria belonging to this genus. Materials and Methods: A phage was isolated from a soil sample, using Mycobacterium smegmatis as host. Its characterization included sequencing, annotation, and analysis of the genome, host range determination, and electron microscopy imaging. Results: Mycobacterium phage vB_MsmS_Celfi is a temperate phage able to infect Mycobacterium tuberculosis with high efficiency. From electron microscopy images, Celfi belongs to the Siphoviridae family. Genome analysis classified phage Celfi into cluster L, subcluster L2 of Actinobacteriophage clusters. Mycobacterium phage Celfi exhibits a Lysin B distant to those present in other members of the subcluster and other mycobacteriophages. Conclusions: The discovery of new phages that infect M. tuberculosis could contribute to the development of novel tools for detection systems and future treatment of the disease.

Introduction: Only a few Lactobacillus casei phages have so far been characterized. As several L. casei strains are part of probiotic formulations, bacteriophage outbreaks targeting these strains can lead to critical losses within the dairy industry.Materials and Methods: A new L. casei phage was isolated from raw milk obtained from a milking yard from the province of Buenos Aires. The phage genome was sequenced, annotated, and analyzed. Morphology was determined by electron microscopy and the host range was established.Results: Lactobacillus phage vB_LcaM_Lbab1 is a member of the Herelleviridae family and features a host range including L. casei/Lactobacillus paracasei and Lactobacillus kefiri strains. We further analyzed the baseplate proteins in silico and found putative carbohydrate binding modules that are responsible for host recognition in other Lactobacillus phages.Conclusions: A new Lactobacillus phage was isolated and characterized. The focus was made on its host recognition mechanism, pointing toward the development of future strategies to avoid deleterious infections in the dairy industry.

Bacterial viruses are widespread and abundant across natural and engineered habitats. They influence ecosystem functioning through interactions with their hosts. Laboratory studies of phage-host pairs have advanced our understanding of phenotypic and genetic diversification in bacteria and phages. However, the dynamics of phage-host interactions has been seldom recorded in complex natural environments. We conducted an observational metagenomic study of the dynamics of interaction between Gordonia and their phages using a three-year data series of samples collected from a full-scale wastewater treatment plant. The aim was to obtain a comprehensive picture of the coevolution dynamics in naturally evolving populations at relatively high time resolution. Co-evolution was followed by monitoring changes over time in the CRISPR loci of Gordonia metagenome-assembled genome, and reciprocal changes in the viral genome. Genome-wide analysis indicated low strain variability of Gordonia , and almost clonal conservation of the trailer-end of the CRISPR loci. Incorporation of newer spacers gave rise to multiple coexisting bacterial populations. A host population containing a CRISPR array variant, which did not contain spacers against the coexisting phages, accounted for more than half of the total host abundance in the majority of samples. Phages genome co-evolved by introducing directional changes, with no preference for mutations within the protospacer and PAM regions. Metagenomic reconstruction of time-resolved variants of host and virus genomes revealed how selection operates at the population level. In activated sludge, it differed from the arms-race observed in nutrient rich media and resembled the fluctuating selection dynamics observed in natural environments.