This image shows leaf yellowing on a Cavendish banana plant in northern Mozambique. The plant was infected by Fusarium oxysporum f. sp. cubense tropical race 4 (TR4), a soil-borne fungus, that affects a range of banana varieties. Once present in a banana field, the fungus cannot be eradicated, making future production of Cavendish bananas almost impossible. In this issue, Zhang et al. show that all Cavendish banana-infecting race 4 strains share a single origin, and that TR4 accessory genes are enriched for virulence and mitochondrion-related functions. The authors also discovered that the fungal nitric oxide biosynthesis pathway is induced upon banana plant infection, suggesting that nitric oxide could be used as a target for disease management.

See Zhang et al.

Microbes and viruses are abundant across terrestrial, freshwater and marine systems, and their behaviours have a profound influence on biogeochemical cycling, the climate, plant and agricultural productivity, and human and animal health. However, our understanding is plagued by unknowns regarding the nature of microbial interactions, the evolution and diversity of these communities, and best practices for studying and conceptualizing the complex dynamics of this unseen majority. This month’s focus issue features a set of Reviews, Perspectives and commentary that span microbial ecology from the organismal to the global scales, shining a light on the research questions that will guide the field.

See Editorial

This image depicts a Rube Goldberg-type representation of the gut microbiota, playfully showing the process of converting various food items into metabolites. In this issue, Quinn-Bohmann et al. have developed a community-scale metabolic modelling approach for predicting personalized short-chain fatty acid production by the gut microbiota in response to prebiotic, probiotic and dietary inputs. Butyrate, a short-chain fatty acid of interest in the paper, is featured as golden stick figures towards the bottom of the composition.

See Quinn-Bohmann et al.

This image shows a bacteriophage on its bacterial host injecting its genome inside the cell where it will reproduce. New bacteriophages burst through the cell wall to find new hosts to infect. In nature, bacteriophages control bacterial populations. Today, they hold potential as a tool in the fight against antimicrobial resistance. A retrospective, observational study reports the efficacy of personalized phage therapy, especially when combined with antibiotics.

See Pirnay et al.

Pseudomonas aeruginosa colonies develop spatial patterns through cooperative swarming. During experimental evolution experiments, cheaters emerged, leading to the disruption of the spatial patterns and a decline in population fitness. The authors found that populations were more vulnerable to invading cheaters in a spatially extended system due to a higher level of cooperation. This collapse of cooperation during microbial range expansion is shown to be tied to its spatial dynamics: spatial structure promoted the invasion of cheaters, while in well-mixed cultures cheaters remained at low frequencies.

See Luo et al.

This image shows fluorescently labelled extracellular vesicles from semen (red) binding to Axl (green), a broadly expressed phosphatidylserine-binding receptor. This interaction interferes with infection by viruses exposing phosphatidylserine to exploit the immunosuppressive uptake mechanism of apoptotic membranes. Given their abundance in semen and saliva, extracellular vesicles may serve as an innate defence against sexual or oral transmission of viruses applying apoptotic mimicry such as Zika, Chikungunya or Ebola.

See Groß et al.

Decomposing remains, whether human or other animal, are attractive to organisms across the tree of life because they are concentrated sources of nutrients and moisture. Blow flies (likely to be Chrysomya rufifacies in this photo), for which larval stages are obligate flesh feeders, are key vectors of a specialist carrion decomposer microbial network that appears universal across terrestrial environments.

See Burcham et al.

This image shows type 10 secretion system (T10SS)-mediated Tc toxin release by Yersinia entomophaga, as captured by cryo-electron tomography. Spanin-mediated membrane fusion triggers bacterial lysis and the explosive discharge of pre-assembled toxins by a subset of the bacterial population.

See Sitsel et al.

This image shows confocal microscopy of macrophages with the DNA-sensing enzyme cGAS (GFP) translocating from the nucleus to the cytosol in response to the phagocytosis of extracellular vesicles isolated from the fungal pathogen Candida albicans.

See Harding et al.