Nutrient driven transcriptional changes during phage infection in an aquatic Gammaproteobacterium

Environment-specific virocell metabolic reprogramming

Viruses impact microbial systems through killing hosts, horizontal gene transfer, and altering cellular metabolism, consequently impacting nutrient cycles. A virus-infected cell, a "virocell," is distinct from its uninfected sister cell as the virus commandeers cellular machinery to produce viruses rather than replicate cells. Problematically, virocell responses to the nutrient-limited conditions that abound in nature are poorly understood. Here we used a systems biology approach to investigate virocell metabolic reprogramming under nutrient limitation. Using transcriptomics, proteomics, lipidomics, and endo- and exo-metabolomics, we assessed how low phosphate (low-P) conditions impacted virocells of a marine Pseudoalteromonas host when independently infected by two unrelated phages (HP1 and HS2). With the combined stresses of infection and nutrient limitation, a set of nested responses were observed. First, low-P imposed common cellular responses on all cells (virocells and uninfected cells), including activating the canonical P-stress response, and decreasing transcription, translation, and extracellular organic matter consumption. Second, low-P imposed infection-specific responses (for both virocells), including enhancing nitrogen assimilation and fatty acid degradation, and decreasing extracellular lipid relative abundance. Third, low-P suggested virocell-specific strategies. Specifically, HS2-virocells regulated gene expression by increasing transcription and ribosomal protein production, whereas HP1-virocells accumulated host proteins, decreased extracellular peptide relative abundance, and invested in broader energy and resource acquisition. These results suggest that although environmental conditions shape metabolism in common ways regardless of infection, virocell-specific strategies exist to support viral replication during nutrient limitation, and a framework now exists for identifying metabolic strategies of nutrient-limited virocells in nature.

Development and characterization of a bacteriophage cocktail with high lytic efficacy against field-isolated Salmonella enterica

Salmonella spp. is a prevalent pathogen that causes great public health concern worldwide. Bacteriophage-based cocktails have arisen as an alternative to antibiotics to inhibit the growth of Salmonella. However, the bactericidal effect of bacteriophage cocktails in vivo largely differs from their observed effect in vitro. This is partly because in vitro developments of cocktails do not always consider the bacterial diversity nor the environmental conditions where bacteriophages will have to replicate. Here, we isolated and sequenced 47 bacteriophages that showed variable degrees of lytic activity against 258 Salmonella isolates from a commercial broiler company in Brazil. Three of these bacteriophages were characterized and selected to assemble a cocktail. In vitro quantitative assays determined the cocktail to be highly effective against multiple serovars of Salmonella, including Minnesota and Heidelberg. Remarkably, the in vitro lytic activity of the cocktail was retained or improved in conditions that more closely resembled the chicken gut, such as anaerobiosis, 42°C, and Salmonella mono-strain biofilms. Analysis of bacterial cross-resistance between the 3 bacteriophages composing the cocktail revealed limited or no generation of cross-resistance. Our results highlight the relevance of an optimized flux of work to develop bacteriophage cocktails against Salmonella with high lytic efficacy and strong potential to be applied in vivo in commercial broiler farms.

Auxiliary Metabolic Gene Functions in Pelagic and Benthic Viruses of the Baltic Sea

Marine microbial communities are facing various ecosystem fluctuations (e.g., temperature, organic matter concentration, salinity, or redox regimes) and thus have to be highly adaptive. This might be supported by the acquisition of auxiliary metabolic genes (AMGs) originating from virus infections. Marine bacteriophages frequently contain AMGs, which allow them to augment their host’s metabolism or enhance virus fitness. These genes encode proteins for the same metabolic functions as their highly similar host homologs. In the present study, we analyzed the diversity, distribution, and composition of marine viruses, focusing on AMGs to identify their putative ecologic role. We analyzed viruses and assemblies of 212 publicly available metagenomes obtained from sediment and water samples across the Baltic Sea. In general, the virus composition in both compartments differed compositionally. While the predominant viral lifestyle was found to be lytic, lysogeny was more prevalent in sediments than in the pelagic samples. The highest proportion of AMGs was identified in the genomes of Myoviridae. Overall, the most abundantly occurring AMGs are encoded for functions that protect viruses from degradation by their hosts, such as methylases. Additionally, some detected AMGs are known to be involved in photosynthesis, 7-cyano-7-deazaguanine synthesis, and cobalamin biosynthesis among other functions. Several AMGs that were identified in this study were previously detected in a large-scale analysis including metagenomes from various origins, i.e., different marine sites, wastewater, and the human gut. This supports the theory of globally conserved core AMGs that are spread over virus genomes, regardless of host or environment.