Genomic evolution of bacterial populations under coselection by antibiotics and phage

Advances in Diversity, Evolutionary Dynamics and Biotechnological Potential of Restriction-Modification Systems

Restriction-modification systems (RMS) are ubiquitous in prokaryotes and serve as primitive immune-like mechanisms that safeguard microbial genomes against foreign genetic elements. Beyond their well-known role in sequence-specific defense, RMS also contribute significantly to genomic stability, drive evolutionary processes, and mitigate the deleterious effects of mutations. This review provides a comprehensive synthesis of current insights into RMS, emphasizing their structural and functional diversity, ecological and evolutionary roles, and expanding applications in biotechnology. By integrating recent advances with an analysis of persisting challenges, we highlight the critical contributions of RMS to both fundamental microbiology and practical applications in biomedicine and industrial biotechnology. Furthermore, we discuss emerging research directions in RMS, particularly in light of novel technologies and the increasing importance of microbial genetics in addressing global health and environmental issues.

Evolving a plant-beneficial bacterium in soil vs. nutrient-rich liquid culture has contrasting effects on in-soil fitness

Inoculation of plant-beneficial microbes into agricultural soils can improve crop growth, but such outcomes depend on microbial survival. Here, we assessed how exposure to prior environmental conditions impacts microbial in-soil fitness, particularly focusing on incubation in liquid culture as an unavoidable phase of inoculant production and on pre-incubation in target soils as a potential method to improve performance. We conducted experimental evolution on a phosphorus-solubilizing bacterial species, Priestia megaterium, in (i) soil only, (ii) liquid media only, and (iii) soil followed by liquid media, using population metagenomic sequencing to track mutations over time. Several typical in vitro evolutionary phenomena were observed in liquid media-incubated populations, including clonal interference, genetic hitchhiking, and mutation parallelism between replicate populations, particularly in the sporulation transcription factor spo0A. Liquid media-incubated populations also developed a clear fitness reduction in soil compared to the ancestral isolate. However, soil-incubated populations grew slowly, experienced far fewer generations despite longer absolute time, and accumulated minimal mutational changes. Correspondingly, soil-incubated populations did not display improved survival compared to the ancestral isolate in their target soils, though there did appear to be minor fitness reductions in unfamiliar soil. This work demonstrates that adaptation to liquid media and/or a native soil can impact bacterial fitness in new soil and that bacterial evolution in more complex real-world habitats does not closely resemble bacterial evolution in liquid media.

IMPORTANCE

Innovative solutions are needed to address emerging challenges in agriculture while reducing its environmental footprint. Management of soil microbiomes could contribute to this effort, as plant growth-promoting microorganisms provide key ecosystem services that support crops. Yet, inoculating beneficial microbes into farm soils yields unreliable results. We require a greater knowledge of the ecology of these taxa to improve their functioning in sustainable agroecosystems. In this report, we demonstrate that exposure to laboratory media and lingering adaptation to another soil can negatively impact the in-soil survival of a phosphorus-solubilizing bacterial species. We go further to highlight the underlying mutations that give rise to these patterns. These insights can be leveraged to improve our understanding of how soil-dwelling beneficial microorganisms adapt to different evolutionary pressures.

Nutrient-rich spatial refuges buffer against extinction and promote evolutionary rescue in evolving microbial populations

Microbial populations are often exposed to long-term abiotic disturbances, which can reduce population viability and cause local extinction. Eco-evolutionary theory suggests that spatial refuges can facilitate persistence and evolutionary rescue. However, one drawback of spatial refuges is reduced exposure to nutrients such as carbon and oxygen, suggesting the protective effect of refuges depends on the interplay between environmental conditions and the degree of stress. Here, we test this general idea using mathematical modelling, and experimental evolution of the model bacterium Pseudomonas fluorescens SBW25 under salinity stress. As our model predicted, we find that the ability of spatial refuges to rescue evolving populations from extinction crucially depends on nutrient availability. Populations evolving under salinity stress where nutrient-rich spatial refuges were available, harboured clones that displayed enhanced salt resistance, indicating that nutrient-rich spatial refuges can facilitate evolutionary rescue. Furthermore, while control-salinity-evolved populations adapted to spatial structure by evolving enhanced motility (likely through parallel mutations in PFLU_4551, a predicted aerotaxis response regulator), this phenotype was constrained under high salinity, because increased motility negates the benefits of a spatial refuge. Our results reveal a general interplay between spatial refuges and nutrient availability that could be leveraged to reduce extinction risk in natural populations.

Phage resistance mutations affecting the bacterial cell surface increase susceptibility to fungi in a model cheese community

Diverse populations of bacteriophages infect and coevolve with their bacterial hosts. Although host recognition and infection occur within microbiomes, the molecular mechanisms underlying host-phage interactions within a community context remain poorly studied. The biofilms (rinds) of aged cheeses contain taxonomically diverse microbial communities that follow reproducible growth patterns and can be manipulated under laboratory conditions. In this study, we use cheese as a model for studying phage-microbe interactions by identifying and characterizing a tractable host-phage pair co-occurring within a model Brie-like community. We isolated a novel bacteriophage, TS33, that kills Hafnia sp. JB232, a member of the model community. TS33 is easily propagated in the lab and naturally co-occurs in the cheese community, rendering it a prime candidate for the study of host-phage interactions. We performed growth assays of the Hafnia, TS33, and the fungal community members, Geotrichum candidum and Penicillium camemberti. Employing Random Barcode Transposon Sequencing experiments, we identified candidate host factors that contribute to TS33 infectivity, many of which are homologs of bacterial O-antigen genes. Hafnia mutants in these genes exhibit decreased susceptibility to phage infection, but experience negative fitness effects in the presence of the fungi. Therefore, mutations in O-antigen biosynthesis homologs may have antagonistic pleiotropic effects in Hafnia that have major consequences for its interactions with the rest of the community. Ongoing and future studies aim to unearth the molecular mechanisms by which the O-antigen of Hafnia mediates its interactions with its viral and fungal partners.

Population dynamics hide phenotypic changes driven by subtle chemical exposures: implications for risk assessments

Ecological risk assessment of chemicals focuses on the response of different taxa in isolation not taking ecological and evolutionary interplay in communities into account. Its consideration would, however, allow for an improved assessment by testing for implications within and across trophic levels and changes in the phenotypic and genotypic diversity within populations. We present a simple experimental system that can be used to evaluate the ecological and evolutionary responses to chemical exposure at microbial community levels. We exposed a microbial model system of the ciliate Tetrahymena thermophila (predator) and the bacterium Pseudomonas fluorescens (prey) to iron released from Magnetic Particles (MP-Fe_dis), which are Phosphorus (P) adsorbents used in lake restoration. Our results show that while the responses of predator single population size differed across concentrations of MP-Fe_dis and the responses of prey from communities differed also across concentration of MP-Fe_dis, the community responses (species ratio) were similar for the different MP-Fe_dis concentrations. Looking further at an evolutionary change in the bacterial preys' defence, we found that MP-Fe_dis drove different patterns and dynamics of defence evolution. Overall, our study shows how similar community dynamics mask changes at evolutionary levels that would be overlooked in the design of current risk assessment protocols where evolutionary approaches are not considered.

Indirect Selection against Antibiotic Resistance via Specialized Plasmid-Dependent Bacteriophages

Antibiotic resistance genes of important Gram-negative bacterial pathogens are residing in mobile genetic elements such as conjugative plasmids. These elements rapidly disperse between cells when antibiotics are present and hence our continuous use of antimicrobials selects for elements that often harbor multiple resistance genes. Plasmid-dependent (or male-specific or, in some cases, pilus-dependent) bacteriophages are bacterial viruses that infect specifically bacteria that carry certain plasmids. The introduction of these specialized phages into a plasmid-abundant bacterial community has many beneficial effects from an anthropocentric viewpoint: the majority of the plasmids are lost while the remaining plasmids acquire mutations that make them untransferable between pathogens. Recently, bacteriophage-based therapies have become a more acceptable choice to treat multi-resistant bacterial infections. Accordingly, there is a possibility to utilize these specialized phages, which are not dependent on any particular pathogenic species or strain but rather on the resistance-providing elements, in order to improve or enlengthen the lifespan of conventional antibiotic approaches. Here, we take a snapshot of the current knowledge of plasmid-dependent bacteriophages.

Silent rain: does the atmosphere-mediated connectivity between microbiomes influence bacterial evolutionary rates?

Air carries a vast number of bacteria and viruses over great distances all the time. This leads to continuous introduction of foreign genetic material to local, established microbial communities. In this perspective, I ask whether this silent rain may have a slowing effect on the overall evolutionary rates in the microbial biosphere. Arguably, the greater the genetic divergence between gene 'donors' and 'recipients', the greater the chance that the gene product has a deleterious epistatic interaction with other gene products in its genetic environment. This is due to the long-term absence of check for mutual compatibility. As such, if an organism is extensively different from other bacteria, genetic innovations are less probable to fit to the genome. Here, genetic innovation would be anything that elevates the fitness of the gene vehicle (e.g. bacterium) over its contemporaries. Adopted innovations increase the fitness of the compatible genome over incompatible ones, thus possibly tempering the pace at which mutations accumulate in existing genomes over generations. I further discuss the transfer of bacteriophages through atmosphere and potential effects that this may have on local dynamics and perhaps phage survival.

Identification of a novel archaea virus, detected in hydrocarbon polluted Hungarian and Canadian samples

Metagenomics is a helpful tool for the analysis of unculturable organisms and viruses. Viruses that target bacteria and archaea play important roles in the microbial diversity of various ecosystems. Here we show that Methanosarcina virus MV (MetMV), the second Methanosarcina sp. virus with a completely determined genome, is characteristic of hydrocarbon pollution in environmental (soil and water) samples. It was highly abundant in Hungarian hydrocarbon polluted samples and its genome was also present in the NCBI SRA database containing reads from hydrocarbon polluted samples collected in Canada, indicating the stability of its niche and the marker feature of this virus. MetMV, as the only currently identified marker virus for pollution in environmental samples, could contribute to the understanding of the complicated network of prokaryotes and their viruses driving the decomposition of environmental pollutants.

Genomics of host-pathogen interactions: challenges and opportunities across ecological and spatiotemporal scales

Evolutionary genomics has recently entered a new era in the study of host-pathogen interactions. A variety of novel genomic techniques has transformed the identification, detection and classification of both hosts and pathogens, allowing a greater resolution that helps decipher their underlying dynamics and provides novel insights into their environmental context. Nevertheless, many challenges to a general understanding of host-pathogen interactions remain, in particular in the synthesis and integration of concepts and findings across a variety of systems and different spatiotemporal and ecological scales. In this perspective we aim to highlight some of the commonalities and complexities across diverse studies of host-pathogen interactions, with a focus on ecological, spatiotemporal variation, and the choice of genomic methods used. We performed a quantitative review of recent literature to investigate links, patterns and potential tradeoffs between the complexity of genomic, ecological and spatiotemporal scales undertaken in individual host-pathogen studies. We found that the majority of studies used whole genome resolution to address their research objectives across a broad range of ecological scales, especially when focusing on the pathogen side of the interaction. Nevertheless, genomic studies conducted in a complex spatiotemporal context are currently rare in the literature. Because processes of host-pathogen interactions can be understood at multiple scales, from molecular-, cellular-, and physiological-scales to the levels of populations and ecosystems, we conclude that a major obstacle for synthesis across diverse host-pathogen systems is that data are collected on widely diverging scales with different degrees of resolution. This disparity not only hampers effective infrastructural organization of the data but also data granularity and accessibility. Comprehensive metadata deposited in association with genomic data in easily accessible databases will allow greater inference across systems in the future, especially when combined with open data standards and practices. The standardization and comparability of such data will facilitate early detection of emerging infectious diseases as well as studies of the impact of anthropogenic stressors, such as climate change, on disease dynamics in humans and wildlife.

Aquaculture as a source of empirical evidence for coevolution between CRISPR-Cas and phage

So far, studies on the bacterial immune system CRISPR-Cas and its ecological and evolutionary effects have been largely limited to laboratory conditions. While providing crucial information on the constituents of CRISPR-Cas, such studies may overlook fundamental components that affect bacterial immunity in natural habitats. Translating laboratory-derived predictions to nature is not a trivial task, owing partly to the instability of natural communities and difficulties in repeated sampling. To this end, we review how aquaculture, the farming of fishes and other aquatic species, may provide suitable semi-natural laboratories for examining the role of CRISPR-Cas in phage/bacterium coevolution. Existing data from disease surveillance conducted in aquaculture, coupled with growing interest towards phage therapy, may have already resulted in large collections of bacterium and phage isolates. These data, combined with premeditated efforts, can provide empirical evidence on phage-bacterium dynamics such as the bacteriophage adherence to mucus hypothesis, phage life cycles and their relationship with CRISPR-Cas and other immune defences. Typing of CRISPR spacer content in pathogenic bacteria can also provide practical information on diversity and origin of isolates during outbreaks. In addition to providing information of CRISPR functionality and phage-bacterium dynamics, aquaculture systems can significantly impact perspectives on design of phage-based disease treatment at the current era of increasing antibiotic resistance. This article is part of a discussion meeting issue 'The ecology and evolution of prokaryotic CRISPR-Cas adaptive immune systems'.

Phage or foe: an insight into the impact of viral predation on microbial communities

Since their discovery, bacteriophages have been traditionally regarded as the natural enemies of bacteria. However, recent advances in molecular biology techniques, especially data from "omics" analyses, have revealed that the interplay between bacterial viruses and their hosts is far more intricate than initially thought. On the one hand, we have become more aware of the impact of viral predation on the composition and genetic makeup of microbial communities thanks to genomic and metagenomic approaches. Moreover, data obtained from transcriptomic, proteomic, and metabolomic studies have shown that responses to phage predation are complex and diverse, varying greatly depending on the bacterial host, phage, and multiplicity of infection. Interestingly, phage exposure may alter different phenotypes, including virulence and biofilm formation. The complexity of the interactions between microbes and their viral predators is also evidenced by the link between quorum-sensing signaling pathways and bacteriophage resistance. Overall, new data increasingly suggests that both temperate and virulent phages have a positive effect on the evolution and adaptation of microbial populations. From this perspective, further research is still necessary to fully understand the interactions between phage and host under conditions that allow co-existence of both populations, reflecting more accurately the dynamics in natural microbial communities.

Whole-genome sequencing reveals the mechanisms for evolution of streptomycin resistance in Lactobacillus plantarum

In this research, we investigated the evolution of streptomycin resistance in Lactobacillus plantarum ATCC14917, which was passaged in medium containing a gradually increasing concentration of streptomycin. After 25 d, the minimum inhibitory concentration (MIC) of L. plantarum ATCC14917 had reached 131,072 µg/mL, which was 8,192-fold higher than the MIC of the original parent isolate. The highly resistant L. plantarum ATCC14917 isolate was then passaged in antibiotic-free medium to determine the stability of resistance. The MIC value of the L. plantarum ATCC14917 isolate decreased to 2,048 µg/mL after 35 d but remained constant thereafter, indicating that resistance was irreversible even in the absence of selection pressure. Whole-genome sequencing of parent isolates, control isolates, and isolates following passage was used to study the resistance mechanism of L. plantarum ATCC14917 to streptomycin and adaptation in the presence and absence of selection pressure. Five mutated genes (single nucleotide polymorphisms and structural variants) were verified in highly resistant L. plantarum ATCC14917 isolates, which were related to ribosomal protein S12, LPXTG-motif cell wall anchor domain protein, LrgA family protein, Ser/Thr phosphatase family protein, and a hypothetical protein that may correlate with resistance to streptomycin. After passage in streptomycin-free medium, only the mutant gene encoding ribosomal protein S12 remained; the other 4 mutant genes had reverted to the wild type as found in the parent isolate. Although the MIC value of L. plantarum ATCC14917 was reduced in the absence of selection pressure, it remained 128-fold higher than the MIC value of the parent isolate, indicating that ribosomal protein S12 may play an important role in streptomycin resistance. Using the mobile elements database, we demonstrated that streptomycin resistance-related genes in L. plantarum ATCC14917 were not located on mobile elements. This research offers a way of combining laboratory evolution techniques and whole-genome sequencing for evaluating antibiotic resistance in probiotics.