The abundance of functional genes, cbbL, nifH, amoA and apsA, and bacterial community structure of intertidal soil from Arabian Sea

The Gulf of Cambay is a trumpet-shaped inlet of the Arabian Sea, located along the west coast of India and confronts a high tidal range with strong water currents. The region belongs to a semi-arid zone and saline alkaline intertidal soils are considered biologically extreme. The selected four soil types (S1–S4) were affected by salinity, alkalinity and sodicity. Soil salinity ranged from 20 to 126 dS/m, soil pH 8.6–10.0 with high sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP). Abundance of the key functional genes like cbbL, nifH, amoA and apsA involved in biogeochemical cycling were targeted using qPCR, which varied from (2.36 ± 0.03) × 104 to (2.87 ± 0.26) × 108, (1.18 ± 0.28) × 106 to (1.01 ± 0.26) × 109, (1.41 ± 0.21) × 106 to (1.29 ± 0.05) × 108 and (8.47 ± 0.23) × 104 to (1.73 ± 0.01) × 106 per gram dry weight, respectively. The microbial community structure revealed that soils S1 and S3 were dominated by phylum Firmicutes whereas S4 and S2 showed an abundance of Proteobacterial clones. These soils also represented Bacteroidetes, Chloroflexi, Actinobacteria, Planctomycetes and Acidobacteria clones. Molecular phylogeny showed a significant variation in the bacterial community distribution among the intertidal soil types. A high number of novel taxonomic units were observed which makes the intertidal zone a unique reservoir of unidentified bacterial taxa that may be explored further.