For centuries, biodiversity has spellbound biologists focusing mainly on macroorganism's diversity and almost neglecting the geographic mediated dynamics of microbial communities. We surveyed the diversity of soil bacteria and archaea along a steep precipitation gradient ranging from the Negev Desert in the south of Israel (<100 mm annual rain) to the Mediterranean forests in the north (>900 mm annual rain). Soil samples were retrieved from triplicate plots at five long-term ecological research stations, collected from two types of patches: plant interspaces and underneath the predominant perennial at each site. The molecular fingerprint of each soil sample was taken using terminal restriction length polymorphism of the 16S rRNA gene to evaluate the bacterial and archaeal community composition and diversity within and across sites. The difference in community compositions was not statistically significant within sites (P=0.33 and 0.77 for bacteria and archaea, respectively), but it differed profoundly by ecosystem type. These differences could largely be explained by the precipitation gradient combined with the vegetation cover: the archaeal and bacterial operational taxonomic units were unique to each climatic region, that is, arid, semiarid and Mediterranean (P=0.0001, for both domains), as well as patch type (P=0.009 and 0.02 for bacteria and archaea, respectively). Our results suggest that unlike macroorganisms that are more diverse in the Mediterranean ecosystems compared with the desert sites, archaeal and bacterial diversities are not constrained by precipitation. However, the community composition is unique to the climate and vegetation cover that delineates each ecosystem.

Explaining the coexistence of competing species is a major challenge in community ecology. In bacterial systems, competition is often driven by the production of bacteriocins, which are narrow-spectrum proteinaceous toxins that serve to kill closely related species, providing the producer better access to limited resources. Bacteriocin producers have been shown to competitively exclude sensitive, nonproducing strains. However, the dynamics between bacteriocin producers, each lethal to its competitor, are largely unknown. In this study, we used in vitro, in vivo and in silico models to study competitive interactions between bacteriocin producers. Two Escherichia coli strains were generated, each carrying a DNA-degrading bacteriocin (colicins E2 and E7). Using reporter-gene assays, we showed that each DNase bacteriocin is not only lethal to its opponent but, at lower doses, can also induce the expression of its opponent's toxin. In a well-mixed habitat, the E2 producer outcompeted its adversary; however, in structured environments (on plates or in mice colons), the two producers coexisted in a spatially ‘frozen’ pattern. Coexistence occurred when the producers were initiated with a clumped spatial distribution. This suggests that a ‘clump’ of each producer can block invasion of the other producer. Agent-based simulation of bacteriocin-mediated competition further showed that mutual exclusion in a structured environment is a relatively robust result. These models imply that colicin-mediated colicin induction enables producers to successfully compete and defend their niche against invaders. This suggests that localized interactions between producers of DNA-degrading toxins can lead to stable coexistence of heterogeneously distributed strains within the bacterial community and to the maintenance of diversity.

Desert soils harbour diverse communities of aerobic bacteria despite lacking substantial organic carbon inputs from vegetation. A major question is therefore how these communities maintain their biodiversity and biomass in these resource-limiting ecosystems. Here, we investigated desert topsoils and biological soil crusts collected along an aridity gradient traversing four climatic regions (sub-humid, semi-arid, arid, and hyper-arid). Metagenomic analysis indicated these communities vary in their capacity to use sunlight, organic compounds, and inorganic compounds as energy sources. Thermoleophilia, Actinobacteria, and Acidimicrobiia were the most abundant and prevalent bacterial classes across the aridity gradient in both topsoils and biocrusts. Contrary to the classical view that these taxa are obligate organoheterotrophs, genome-resolved analysis suggested they are metabolically flexible, with the capacity to also use atmospheric H₂ to support aerobic respiration and often carbon fixation. In contrast, Cyanobacteria were patchily distributed and only abundant in certain biocrusts. Activity measurements profiled how aerobic H₂ oxidation, chemosynthetic CO₂ fixation, and photosynthesis varied with aridity. Cell-specific rates of atmospheric H₂ consumption increased 143-fold along the aridity gradient, correlating with increased abundance of high-affinity hydrogenases. Photosynthetic and chemosynthetic primary production co-occurred throughout the gradient, with photosynthesis dominant in biocrusts and chemosynthesis dominant in arid and hyper-arid soils. Altogether, these findings suggest that the major bacterial lineages inhabiting hot deserts use different strategies for energy and carbon acquisition depending on resource availability. Moreover, they highlight the previously overlooked roles of Actinobacteriota as abundant primary producers and trace gases as critical energy sources supporting productivity and resilience of desert ecosystems.