Comprehensive profiles of sulfur cycling microbial communities along a mangrove sediment depth

The vertical distribution and metabolic versatility of complete ammonia oxidizing communities in mangrove sediments

Recently discovered complete ammonia-oxidizing (comammox) microorganisms can completely oxidize ammonia to nitrate and play an important role in the nitrogen (N) cycle across various ecosystems. However, little is known about the vertical distribution and metabolic versatility of comammox communities in mangrove ecosystems. Here we profiled comammox communities from deep sediments (up to 5 m) in a mangrove wetland by combining metagenome sequencing and physicochemical properties analysis. Our results showed that the relative abundance of comammox bacteria (23.2 %) was higher than ammonia-oxidizing bacteria (AOB, 12.0 %), but lower than ammonia-oxidizing archaea (AOA, 64.8 %). The abundance of comammox communities significantly (p < 0.01) decreased with the sediment depth, and dissolved organic carbon and total sulfur appeared to be major environmental factors influencing the nitrifying microbial community structure. We also recovered a high-quality metagenome-assembled genome (MAG) of comammox bacteria (Nitrospira sp. bin2030) affiliated with comammox clade A. Nitrospira sp. bin2030 possessed diverse metabolic processes, not only the key genes for ammonia oxidation and urea utilization in the N cycle, but also key genes involved in carbon and energy metabolisms, sulfur metabolism, and environmental adaptation (e.g., oxidative stress, salinity, temperature, heavy metal tolerance). The findings advance our understanding of vertical distribution and metabolic versatility of comammox communities in mangrove sediments, having important implications for quantifying their contribution to nitrification processes in mangrove ecosystems.

Spatial characteristics of microbial communities and their functions in sediments of subtropical Beibu Gulf, China

Understanding the intricate relationship between marine geography and microbial functions is crucial for marine conservation and management. In this study, we conducted a comprehensive analysis of bacterial composition and function in nearshore and offshore sediments of the Beibu Gulf using 16S rRNA high-throughput sequencing. The results showed that Proteobacteria (average relative abundance: 27.07 %) and Desulfobacterota (average relative abundance: 12.28 %) were the most dominant phyla across all stations, while Woeseiaceae (3.26 %-8.31 %) and Anaerolineaceae (0.61 %-7.43 %) could serve as potential indicator species for pollution. In our study area, the α-diversity of bacterial communities in sediment samples showed an initial increase from coastal to offshore regions, followed by a decrease with further distance from the coastlines. The composition of sediment bacterial communities was mainly influenced by total phosphorus (R2 = 0.183, p < 0.01) and salinity (R2 = 0.550, p < 0.01). Furthermore, the sulfur (S) cycling genes of KEGG pathways displayed significant variations with the distance from shore, implying that S oxidation dominated in nearshore sediments, while S reduction occurred mainly in offshore sediments, which was attributed to the differences in redox conditions across diverse marine environments. These findings will not only enhance our current understanding of the intricate relationship between marine geography and microbial functions but also contribute to elucidating the biogeochemical characteristics of the Beibu Gulf. This research will provide valuable information and a solid scientific basis for the conservation and management of various marine areas.

Metagenomic surveillance reveals different structure and function of microbial community associated with mangrove pneumatophores and their surrounding matrices

Present research employed metagenomics to explore the structural and functional diversity of microorganisms in two matrices of pneumatophore: adhered sediments (PS) and epiphytes (PE) of Avicennia marina. These were compared with microorganisms in surrounding environments: tidal water (TW), mudflat sediment (MF) and mangrove sediment (MS). Results revealed that bacteria made up over 95 % of the microbial community across all five matrices, with the dominance of phylum Proteobacteria, because of their metabolic flexibility and ability to survive in harsh mangrove environment. The bacterial community in PS and PE were similar to TW but differed from those in MF and MS, implying their provenance from TW. The high relative abundance of genes involved in nitrate and sulfur reduction pathways in PS and PE indicates pneumatophore bacteria helps in enhancing nitrogen and sulfur availability. This study is the first to explore the functional significance of pneumatophore-adhered prokaryotic communities using metagenomics.

The vertical partitioning between denitrification and dissimilatory nitrate reduction to ammonium of coastal mangrove sediment microbiomes

Mangrove aquatic ecosystems receive substantial nitrogen (N) inputs from both land and sea, playing critical roles in modulating coastal N fluxes. The microbially-mediated competition between denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in mangrove sediments significantly impacts the N fate and transformation processes. Despite their recognized role in N loss or retention in surface sediments, how these two processes vary with sediment depths and their influential factors remain elusive. Here, we employed a comprehensive approach combining 15N isotope tracer, quantitative PCR (qPCR) and metagenomics to verify the vertical dynamics of denitrification and DNRA across five 100-cm mangrove sediment cores. Our results revealed a clear vertical partitioning, with denitrification dominated in 0-30 cm sediments, while DNRA played a greater role with increasing depths. Quantification of denitrification and DNRA functional genes further explained this phenomenon. Taxonomic analysis identified Pseudomonadota as the primary denitrification group, while Planctomycetota and Pseudomonadota exhibited high proportion in DNRA group. Furthermore, genome-resolved metagenomics revealed multiple salt-tolerance strategies and aromatic compound utilization potential in denitrification assemblages. This allowed denitrification to dominate in oxygen-fluctuating and higher-salinity surface sediments. However, the elevated C/N in anaerobic deep sediments favored DNRA, tending to generate biologically available NH4+. Together, our results uncover the depth-related variations in the microbially-mediated competition between denitrification and DNRA, regulating N dynamics in mangrove ecosystems.