Azahara Navarro

The Sahara Desert and the Sahel region in North Africa contribute approximately 50–70% of global atmospheric dust emissions. Microorganisms can attach to dust particles and be dispersed into exogenous environments, being subsequently deposited by gravitational sedimentation (dry deposition) or through aqueous precipitation (wet deposition) also known as muddy rain. In the present work, five muddy rain samples were collected in Granada (Spain) during different episodes in 2021–2022. The SEM-EDX study demonstrated a high content of fine clay particles which may facilitate the atmospheric transport of microorganisms. The colonization of strategic microsites and the formation of mineral aggregates might be possible mineral-bacteria interactions. According to metagenomic analysis, Pseudomonadota (64%), Bacteroidota (13%), and Bacillota (6%) were the main phyla. At the genus level, extremophiles, plant-beneficial bacteria, and others involved in soil biogeochemical cycles have been described. Fourteen cultivable microorganisms were isolated and identified by means of 16S rRNA sequencing. Members of the phyla Pseudomonadota, Bacillota, Actinomycetota and Bacteroidota have been found. Among the isolates, Stenotrophomonas rhizophila and Brevundimonas bullata potentially exert beneficial effects at the ecosystem level. In general, muddy rain facilitates the transport and dispersal of microorganisms from different environments, with a potential positive influence on soils and vegetation in terrestrial ecosystems.

Climate change negatively affects agriculture, causing desertification, salinisation, and drought. The biochar hydroinfiltrator (ES Patent No.: ES2793448 B2) is a device that increases the capture of rainwater or irrigation water for crops by increasing infiltration rates. Biochar, produced via biomass pyrolysis, has emerged as a promising agricultural amendment, as it helps to optimise moisture retention and improve soil structure, key aspects for boosting crop yields. There is growing interest in microorganisms’ plant-growth-promoting activity (PGP) by carrying out different activities considered growth promoters. The aim of the present study is to evaluate the use of a biochar hydroinfiltrator as a promoter of microbial activity when it is used in soil. Metagenomic analysis of soils with and without the device reveals that genera Bacillus and Sphingomonas became particularly enriched in soils with hydroinfiltrators. Also, in order to understand the interaction between the uses of biochar together with bacteria PGP, an in vitro test was carried out. Two microorganisms, previously selected for their characteristics as plant growth promoters, were inoculated in soils with and without biochar and they grew better after 15 to 30 days of inoculation, showing major CFU counts. This combined strategy—biochar hydroinfiltrator and PGP bacteria—offers an innovative, eco-friendly approach to sustainable agriculture, particularly under drought stress.

Global warming due to climate change has increased the frequency of sand and dust storms that affect air quality and ecosystems in general, contributing to air pollution. The Sahara Desert is the most potent emitter of atmospheric dust. The atmosphere is an extreme environment and microorganisms living in the troposphere are exposed to greater ultraviolet radiation, desiccation, low temperatures and nutrient deprivation than in other habitats. The Iberian Peninsula, and specifically the Canary Islands—due to its strategic location—is one of the regions that receive more Saharan dust particles annually, increasing year after year, although culturable microorganisms had previously never been described. In the present work, dust samples were collected from three calima events in the Canary Islands between 2021 and 2022. The sizes, mineralogical compositions and chemical compositions of dust particles were determined by laser diffraction, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Particle morphology and biological features were also studied by scanning electron microscopy (SEM-EDX) and confocal laser scanning microscopy (CLSM). The mineral–bacteria interactions were described from microscopic observations, which revealed the presence of iberulites and small neoformed kaolinite crystals in association with bacteria. This article defines the term “mineral atmospherogenesis” and its variant, “mineral bioatmospherogenesis”, through microbial interaction. This is the first described case of kaolinite produced through mineral bioatmospherogenesis. The bacterial growth in atmospheric dust was illustrated in SEM images, constituting a novel finding. Twenty-three culturable microorganisms were isolated and identified by 16S rRNA sequencing. Members of the phyla Pseudomonadota, Bacillota and Actinomycetota have been found. Some of these microorganisms, such as Peribacillus frigoritolerans, have Plant Growth-Promoting Rhizobacteria (PGPR) properties. Potential human pathogenic bacteria such as Acinetobacter lwoffii were also found. The presence of desert dust and iberulites in the Canary Islands, together with transported biological components such as bacteria, could have a significant impact on the ecosystem and human health.