Assessment of Microbial Composition and Heavy Metals in Wetland Soils of the Niger Delta, Nigeria

Wetland ecosystems rely heavily on soil microorganisms to drive nutrient cycling and regulate biogeochemical processes. Despite their ecological importance, the composition and functional networks of microbial communities in Niger Delta wetlands remain poorly characterized. In this study, microbial composition of wetland soils from Akwa Ibom, Bayelsa, and Rivers States were investigated using both culture-dependent and culture-independent approaches. Archaeal communities were represented predominantly by Euryarchaeota (39.41%), Thaumarchaeota (32.96%), Candidatus Thermoplasmatota (16.61%), Crenarchaeota (9.86%), and Candidatus Korarchaeota. Microbial population densities revealed total heterotrophic bacteria ranging between 1.7 × 10^-6 and 2.3 × 10^-8 cfu/g, phosphate-solubilizing bacteria between 1.2 × 10^-5 and 1.4 × 10^-7 cfu/g, and nitrogen-reducing bacteria between 3.0 × 10^-4 and 1.6 × 10^-7 cfu/g. Culture-based identification highlighted taxa such as Bacillus cereus, Bacillus subtilis, Clostridium sp., Desulfovibrio sp., Micrococcus sp., Serratia sp., Pseudomonas spp., Staphylococcus sp., Pseudomonas putida, Nitrobacter sp., Chromatium sp., Nitrosomonas, and Azotobacter sp. Molecular analysis further revealed nitrogen-fixing potential, with Klebsiella pneumoniae subsp. pneumoniae HS11286, Enterobacter mori, and Roseomonas rhizosphaerae amplifying the nifH gene. Heavy metal concentrations were quantified, with iron (349.64 ± 0.15–539.98 ± 0.90 mg/kg) dominating, followed by zinc (18.56 ± 0.13–56.41 ± 0.50 mg/kg), copper (4.19 ± 1.20–8.14 ± 0.70 mg/kg), chromium (2.42 ± 0.06–3.99 ± 0.13 mg/kg), and nickel (1.12 ± 0.04–2.11 ± 0.06 mg/kg), while cadmium and vanadium consistently remained below detection limits (<0.01 mg/kg). These findings provide the first comprehensive baseline of microbial and heavy metal characteristics of Niger Delta wetland soils, offering critical insights for sustainable management and agricultural productivity.