The Gran Desierto de Altar, located in Sonora, Mexico, represents an arid region that offers an opportunity to study microbial life under extreme conditions. This study analyzed the bacterial diversity present in two distinct types of desert sediments: sand dunes (SDs) and salt crusts (SCs) by culture-dependent and culture-independent methods. Environmental DNA was obtained for 16S rRNA gene amplicon sequencing to obtain taxonomic information using QIIME2. In SD, the bacterial communities comprised 24 phyla, with Actinobacteriota (30–40%), Proteobacteria (22–27%), Bacteroidota (9–11%), Firmicutes (7–10%), and Chloroflexi (3–6%) emerging as the most abundant. Notably, in SC, the archaeal phylum Halobacterota was predominant (37–58%). SC hosted 12 bacterial phyla, the most abundant being Firmicutes (14–30%), Bacteroidota (3–24%), and Proteobacteria (1–12%). Bacteria belonging to the phylum Firmicutes, including Metabacillus niabensis, Bacillus subtilis, Bacillus licheniformis, and Alkalibacillus haloalkaliphilus, were isolated using nutrient and saline media. Overall, our findings indicate that the taxonomic composition of the samples analyzed from the Gran Desierto de Altar is consistent with that found in arid environments worldwide. This study provides a basis for future studies focusing on microbial diversity, genetic potentials, and resistance mechanisms of microorganisms from arid environments.

Pine forests and shrublands worldwide are increasingly threatened by wildfires driven by global change, and those of temperate-humid ecosystems are no exception. Although the impact of soil bacterial of soil burn severity (SBS) on bacterial communities, has been examined in a number of studies, knowledge about their response across gradients of high SBS levels remains limited. In this study, we assessed the early effect (six weeks post-wildfire) of an SBS gradient, from moderate to extreme, previously defined, on bacterial communities in topsoil (0-2 cm) under adjacent pine and shrubland vegetation in northwestern Spain. Alpha diversity declined under moderate SBS, but no further decrease was observed at higher severity. Beta diversity increased, but community composition stabilized from moderate severity onwards, suggesting a threshold above which further compositional shifts are limited. Burned soils were enriched in Proteobacteria, Bacteroidetes, and Firmicutes, while Acidobacteria and Actinobacteria declined. Known pyrophilic genera (e.g. Massilia, Pedobacter), and others not previously reported with that character, were more abundant in burned soils. However, their increase did not extend beyond moderate SBS, reinforcing the notion of a compositional threshold. This stabilization may reflect the fire selection of fire-adapted communities' composition. Vegetation type, although a weaker driver than SBS, modulated bacterial responses: unburned pine and shrubland soils hosted similar communities that diverged after fire, with shrubland soils showing greater sensitivity. Soil pH, C, and C/N were strongly associated with bacterial composition. Our study provides evidence that moderate SBS may be sufficient to drive major shifts in soil bacterial communities, and that higher SBS levels do not necessarily lead to further changes, although confirmation through new studies is needed. The study findings may be useful for developing methods of accelerating the recovery of burned soils.

Symbiotic relationships between plants and bacteria play a pivotal role in both natural and agricultural ecosystems, particularly through endophytic colonization or rhizospheric interactions. This study evaluated the plant growth-promoting potential (PGP) of native rhizobial strains Rhizobium sp. ACO-34A and Mesorhizobium sp. 28A (now reclassified within the genus Kumtagia), isolated from Agave americana. Through phenotypic characterization, PGP evaluation, and comparative genomic analysis, both strains demonstrated the ability to thrive under diverse salinity levels and pH conditions, reflecting their adaptability to challenging environments. Rhizobium sp. ACO-34A exhibited superior resistance to antibiotics and heavy metals, coupled with robust PGP traits, such as phosphate solubilization and indole-3-acetic acid (IAA) production, which are crucial for enhancing nutrient availability and root development. Similarly, Mesorhizobium sp. 28A showed exceptional phosphate solubilization efficiency and contributed to improved seedling performance. These findings highlight the capacity of rhizobia associated with agave species to improve plant growth, reduce dependence on chemical fertilizers, and support sustainable agriculture, particularly in nutrient-depleted or semi-arid soils. Genomic analyses revealed the presence of genes linked to stress resilience and nutrient acquisition, underlining the functional versatility of these strains. By leveraging these native rhizobial strains, agricultural practices can achieve higher productivity and sustainability, making them valuable tools for enhancing the agronomic yield and ecological resilience of agave crops for agro-industries.

Six bacteria (Bacillus velezensis 13, Bacillus subtillis 42, Pseudomonas fluorescens E221, Pseudomonas Poae EE12, Rahnella sp. EM1, and Serratia sp. EM2) isolated from the soil and litter of Mexican oak forests were characterized by identifying their ability to acquire phosphorus from different sources, analyzed for their biocontrol capabilities against two different phytopathogenic fungi, and finally tested for their ability to stimulate the germination of maize seeds and promotion of maize seedling growth. The greatest capacity to biocontrol the mycelial growth of phytopathogenic fungi Botrytis cinerea and Fusarium oxysporum was found in B. velezensis 13 and B. subtillis 42. P. poae EE12 and P. fluorescens E221 significantly promoted germination and the length of the primary root in Zea mays. Rahnella sp. EM1 and Serratia sp. EM2 could produce indole compounds related to auxin synthesis and increased the fresh weight of the maize seedlings. Together, these isolates represent an alternative to reduce the use of agrochemicals in maize cultivation. In general, soil microorganisms from Mexican oak forests represent a source of genetic resources for the sustainable management and conservation of soils for agricultural use.