Dust events, when thousands of tonnes of fine sand whipped up from the Sahara are dumped over Europe, are becoming more intense. These sometimes produce “blood rain” that leaves visible red streaks, and while generally harmless, the dust is not sterile but brings a freight of microorganisms.

One big concern is how imported microbes may affect the soil microbiome and impact agricultural fertility and crop yield. Southern Portugal lies along one of the main deposition routes for Saharan dust, and the effect on vineyards in particular is a growing concern. A team from the University of Lisbon carried out genomic mapping of microbes in dust samples from 2022’s Storm Celia.

In addition to other findings the study turned up one surprise: a genus of bacteria that could benefit crop growth. Researchers say the strains of resilient bacteria in the dust can integrate into European soil. These may act as plant growth-promoting rhizobacteria (PGPR), which chemically alter the environment around plant roots to unlock nutrients and stimulate growth, acting as natural fertiliser.

Blood rain may bring benefits as well as harms, in particular supplying soil bacteria suitable for hot, dry conditions. Researchers are pressing ahead to understand microbe transport, and how best to counter the threats and exploit the opportunities.