Abstract
In subduction zones, serpentinization and biological processes may release alkanes to the deep waters, which would probably result in the rapid spread of Alcanivorax However, the timing and area of the alkane distribution and associated enrichment of alkane-degrading microbes in the dark world of the deep ocean have not been explored. In this study, we report the richness (up to 17.8%) of alkane-degrading bacteria, represented by Alcanivorax jadensis, in deep water samples obtained at 3,000 to 6,000 m in the Mariana Trench in two cruises. The relative abundance of A. jadensis correlated with copy numbers of functional almA and alkB genes, which are involved in alkane degradation. In these water samples, we detected a high flux of alkanes, which probably resulted in the prevalence of A. jadensis in the deep waters. Contigs of A. jadensis were binned from the metagenomes for examination of alkane degradation pathways and deep sea-specific pathways, which revealed a lack of nitrate and nitrite dissimilatory reduction in our A. jadensis strains. Comparing the results for the two cruises conducted close to each other, we suggest periodic release of alkanes that may spread widely but periodically in the trench. Distribution of alkane-degrading bacteria in the world's oceans suggests the periodic and remarkable contributions of Alcanivorax to the deep sea organic carbon and nitrogen sources.IMPORTANCE In the oligotrophic environment of the Mariana Trench, alkanes as carbohydrates are important for the ecosystem, but their spatial and periodic spreading in deep waters has never been reported. Alkane-degrading bacteria such as Alcanivorax spp. are biological signals of the alkane distribution. In the present study, Alcanivorax was abundant in some waters, at depths of up to 6,000 m, in the Mariana Trench. Genomic, transcriptomic, and chemical analyses provide evidence for the presence and activities of Alcanivorax jadensis in deep sea zones. The periodic spreading of alkanes, probably from the subductive plates, might have fundamentally modified the local microbial communities, as well as perhaps the deep sea microenvironment.
Highlights
In subduction zones, serpentinization and biological processes may release alkanes to the deep waters, which would probably result in the rapid spread of Alcanivorax
Alcanivorax borkumensis SK2 and Alcanivorax jadensis T9 are able to utilize n-alkanes ranging from C5 to C32, depending on the alk and alm gene families, which are specialized for intermediate- and high-molecular-weight alkanes, respectively [18, 19]
The results showed that the relative abundance of Alcanivorax peaked at 17.8% in the 3,000-m water layer of the R/V Dayang no. 37-II (DY37II) conductivity, temperature, and depth 07 (CTD07) site (Fig. 1B)
Summary
Serpentinization and biological processes may release alkanes to the deep waters, which would probably result in the rapid spread of Alcanivorax. We report the richness (up to 17.8%) of alkane-degrading bacteria, represented by Alcanivorax jadensis, in deep water samples obtained at 3,000 to 6,000 m in the Mariana Trench in two cruises. Distribution of alkane-degrading bacteria in the world’s oceans suggests the periodic and remarkable contributions of Alcanivorax to the deep sea organic carbon and nitrogen sources. We sampled the water columns in the Mariana Trench, aiming to answer the questions regarding the spreading of alkanes in the subduction zone and the contribution of hydrocarbons to the ecosystem of deep waters. The high concentrations of alkanes remarkably correlated with the richness of A. jadensis, indicating the spreading of alkanes in the formation of plumes
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