Nitrogen-transforming microorganisms shape global biogeochemical nutrient cycles. In this Review, Kuypers, Marchant and Kartal explore the vast diversity of these microorganisms and their enzymes, highlighting novel pathways, and discuss how nitrogen-transforming microorganisms form complex nitrogen-cycling networks in different environments.

Bacterial microcompartments are self-assembling organelles that consist of an enzymatic core that is encapsulated by a selectively permeable protein shell. In this Review, Kerfeld and colleagues discuss recent insights into the structure, assembly, diversity and function of bacterial microcompartments.

Rhizobia can exist as both free-living soil microbiota and plant-associated endosymbionts, which form N₂-fixing root nodules. In this Review, Poole, Ramachandran and Terpolilli explore the drastic lifestyle shift that underlies this transition and the associated plant–bacteria interactions.

Hopanoid lipids are structurally and functionally related to sterols, which are important building blocks of membranes. In this Review, Newman, Silipo and colleagues explore the diversity of bacterial hopanoids and their roles in stress adaptation and plant symbiosis.

This Focus issue on biogeochemistry highlights the metabolic versatility in microbial communities and the significance of microbial contributions to the flow of elements in Earth's biogeochemical cycles.

Two new studies highlight the potential impact of climate change on microbial biogeochemical cycles.

Infection ofE. huxleyiby coccolithoviruses facilitates downward vertical flux of both particulate organic and inorganic carbon, thus enhancing the efficiency of carbon export into the deep ocean.

Two new studies explore the diverse microorganisms and their enzymes that contribute to the global sulfur cycle.