This study examined culturable bacterial communities and physicochemical properties across ten governorates in the Makkah Region of Saudi Arabia, focusing on how environmental gradients shape bacterial community structure. A total of fifty soil samples were collected from coastal, peri-coastal, and inland locations. Standard protocols were used to measure soil pH, moisture content, and particle size distribution. Through serial dilution and inoculation on selective media, one hundred bacterial isolates were obtained. Phylogenetic relationships were inferred using 16S rRNA gene sequencing and neighbor-joining methods, and taxonomic assignments were further supported by secondary structure analysis. Soil pH ranged from 7.00-7.81, while moisture content differed by a factor of 24 (0.5%-12.0%) between governorates. The number of isolates abundance per governorate varied from 6 to 20, including three strains of Staphylococcus hominis and four Gram-negative taxa: Pseudomonas aeruginosa, Erwinia phyllosphaerae, Xanthomonas maliensis, and Dyella marensis. SNP analysis identified 3-14 nucleotide substitutions per isolate, corresponding to divergence levels of 0.29%-1.40%. Despite its low moisture content, Fair Capital Governorate yielded an unexpectedly large number of isolates, indicating possible human-driven alterations to soil conditions. SEM observations revealed marked differences in biofilm colonization patterns that correlated with soil texture and moisture levels. By integrating cultivation-based isolation, molecular identification, phylogenetic reconstruction, and secondary structure validation, this study advances understanding of bacterial diversity in the arid terrestrial habitats of Western Saudi Arabia and sheds light on microbial strategies for adapting to extreme environments.
Soil Microbiota, Bacterial Diversity, 16S rRNA Gene Sequencing, Makkah Region, Soil Physicochemical Properties
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