The cover shows electron micrographs of phage ΦAP1.1. This phage utilizes a two-pronged approach to disable CRISPR immunity in Streptococcus pyogenes: first, by producing a protein inhibitor of Cas9 during the lytic portion of its life cycle, and second, by using a site-specific integrase to insert the prophage into the CRISPR array during lysogeny

See Varble et al

Shown are Emiliania huxleyi coccolithophores, which are falsely coloured and have been chosen to represent a traffic control system in the ocean, and the findings of Adva Shemi, Assaf Vardi and colleagues, who show that production of dimethyl sulfide by algae can attract predators and increase predation by zooplankton, thereby mediating predator–prey relationships in the ocean.

See Shemi, A. et al

Shown are a selection of arthropods, chosen to illustrate the findings of Brekhna Hassan, Timothy Walsh and colleagues. Over two seasons, the researchers sampled several areas in and around a semi-rural hospital in Pakistan to analyse transmission networks of multi-drug-resistant Enterobacterales involving arthropods, including flying and crawling insects, on hospital surfaces and in post-surgical site infections. They conclude that insect and pest control should be implemented in hospitals to limit the spread of anti-microbial resistance, which in turn would improve patient outcomes.

See Hassan et al.

Most of the nitrate in nature is produced by bacteria, which rely on the nitrite oxidoreductase (NXR) multiprotein complex to oxidize nitrite to nitrate. Tadeo Moreno Chicano, Lea Dietrich, Naomi M. de Almeida and colleagues used a combination of biochemical and structural analyses to elucidate the mechanisms governing the assembly and function of this filament-forming complex from the anaerobic ammonium-oxidizing (anammox) bacterium Kuenenia stuttgartiensis. Shown is a view of a reconstructed NXR tubule down its long axis.

See Chicano, T. M. et al.

Shown is a cryo-electron microscopy image of chains of Aspergillus conidia (spores) attached to an intact conidiophore. Koon Ho Wong and colleagues use chromatin immunoprecipitation followed by sequencing and RNA-sequencing analyses to show that the transcriptional activity of fungal conidia before dormancy contributes to conidia maturation and impacts fitness, drug resistance and virulence following germination.

See Wang, F. et al.

Shown are Lassa virus particles. Xin Xu, Ruchao Peng, Qi Peng and colleagues use cryo-electron microscopy to show how Lassa and Machupo virus Z proteins bind the viral L polymerase at resolutions of 3.1–3.9 Å, and use these structures to deduce how this binding inhibits virus replication.

See Xu, X. et al.

Shown are stepwise stages in bacterial flagellum assembly deduced from multiple structures. Steven Johnson and colleagues use cryo-electron microscopy to solve structures of the intact Salmonella flagellar basal body, including the inner membrane rotor, drive shaft and outer-membrane bushing, to resolutions of 2.2–3.7 Å. These structures provide detailed views of the outer membrane LP-ring and the entire flagellar rod and hook cap complex, and reveal how multiple proteins assemble into a macromolecular machine that spans two membranes and a cell wall.

See Johnson, S. et al.

The archaeal model organism, Haloferax volcanii, is a common inhabitant of salt lakes around the globe, such as the partly dry Lake Gairdner in South Australia, shown here. Using H. volcanii, Liao and colleagues performed a functional analysis of the two tubulin-like FtsZ proteins found in many archaea, showing that they have differing roles in cell division: FtsZ1 directs the proper assembly of FtsZ2 at midcell, and FtsZ2 then divides the cell in two. In this issue, Yang et al. and Squyres, Holmes et al. also investigate cell division, using single-molecule imaging to elucidate the dynamics of divisome proteins in the model bacteria Escherichia coli and Bacillus subtilis, respectively.

See Liao, Y. et al.; Yang, X. et al.; and Squyres, G. R. et al.

Shown is a San Clemente Island goat named Elway, housed at Santa Barbara Zoo in the United States. Xuefeng Peng and colleagues, working in a team led by Professor Michelle O’Malley, used faecal pellets from this goat to set up more than 400 parallel enrichment cultures. They characterized how substrate selection and antibiotic treatment affect the membership, activity, stability and chemical productivity of herbivore gut microbiomes. The overarching aim of their research is to understand how microbial consortia break down lignocellulose, and to use that knowledge to design synthetic consortia for the bioconversion of lignocellulose into value-added chemicals.

See Peng, X. et al.

Shown is an artistic representation of the potential and flexibility of CRISPRi (CRISPR interference), which enables multiple genetic screens to be carried out in numerous strains of Escherichia coli simultaneously. Here, dCas9 (dark blue blobs) is shown targeting specific genes and loci and, in doing so, providing researchers with information about the genes themselves, including the identification of extensive variations in gene essentiality between strains and conditions. This type of approach could readily be applied to evaluate the pan-essential genome in other bacterial species.

See Rousset, F. et al.

This detailed sketch by Dean Jacobson (1957–2018) illustrates the tremendous morphological diversity of free-living dinoflagellates. Their physiology, life cycles and taxonomic identity are underexplored in the open ocean, and their roles in marine carbon cycling are unclear. In their accompanying Article, Saito et al. describe the distinct strategies that dinoflagellates use to acquire carbon and nutrients across the vast central Pacific Ocean and their contributions to marine biogeochemistry.

See Saito, M. A. et al.

Shown are Escherichia coli and the cheese-associated bacterium Pseudomonas psychrophila growing with a cheese-associated Penicillium fungus. Pierce and colleagues study the interactions between fungi and bacteria in microbiomes. They combine random barcode transposon-site sequencing, RNA sequencing, bacterial cytological profiling and metabolomics to reveal that fungi can affect the fitness of bacterial mutants through a variety of mechanisms. Their findings may translate to a better understanding of the effects of fungi on bacterial phenotypes in mixed-species microbiomes.

See Pierce, E. C. et al.