Fine-scale metabolic discontinuity in a stratified prokaryote microbiome of a Red Sea deep halocline

Abstract

Deep-sea hypersaline anoxic basins are polyextreme environments in the ocean’s interior characterized by the high density of brines that prevents mixing with the overlaying seawater, generating sharp chemoclines and redoxclines up to tens of meters thick that host a high concentration of microbial communities. Yet, a fundamental understanding of how such pycnoclines shape microbial life and the associated biogeochemical processes at a fine scale, remains elusive. Here, we applied high-precision sampling of the brine–seawater transition interface in the Suakin Deep, located at 2770 m in the central Red Sea, to reveal previously undocumented fine-scale community structuring and succession of metabolic groups along a salinity gradient only 1 m thick. Metagenomic profiling at a 10-cm-scale resolution highlighted spatial organization of key metabolic pathways and corresponding microbial functional units, emphasizing the prominent role and significance of salinity and oxygen in shaping their ecology. Nitrogen cycling processes are especially affected by the redoxcline with ammonia oxidation processes being taxa and layers specific, highlighting also the presence of novel microorganisms, such as novel Thaumarchaeota and anammox, adapted to the changing conditions of the chemocline. The findings render the transition zone as a critical niche for nitrogen cycling, with complementary metabolic networks, in turn underscoring the biogeochemical complexity of deep-sea brines.

Age, metabolisms, and potential origin of dominant anammox bacteria in the global oxygen-deficient zones

“…1A ), including SRR1509794_bin.7 (NCBI accession CAJXKT000000000) recovered from the ODZ core of ETNP (125 m depth at 18.9°N 104.5°W) based on existing metagenome sequencing data [ 47 ] and Ca. Scalindua arabica [ 84 ] recovered from the anoxic waters of the Red Sea deep halocline. ODZ_B exhibits a 99.1% AAI with SRR1509794_bin.7 and 91.2% with Ca.…”

“…This observation provides strong support for the previous observation that urea can enhance anammox rates in the ETSP ODZ [ 13 ]. Urea concentrations of up to 2 μM have been detected in both oxic and anoxic seawater [ 19 , 84 ], while concentrations of ammonium in ODZ waters are only on the order of tens to hundreds of nanomolars [ 13 , 102 ], indicating that urea can be important for ODZ anammox bacteria when ammonium is limiting. In contrast to cyanate, urease is not widespread in anammox bacteria or the Ca.…”

Origin, age, and metabolisms of dominant anammox bacteria in the global oxygen deficient zones

“…1A), including SRR1509794_bin.7 recovered from the ODZ core of ETNP (125 m depth at 18.9°N 104.5°W) based on existing metagenome sequencing data 26 , and Ca. Scalindua arabica 27 recovered from anoxic waters of the Red Sea deep halocline. ODZ_B exhibits a 99.1% AAI with SRR1509794_bin.7 and 91.2% with Ca.…”

“…This observation provides strong support for the previous observation that urea can enhance anammox rates in the ETSP ODZ 13 . Urea concentrations of up to 2 µM have been detected in both oxic and anoxic seawater 17, 27 , while concentrations of ammonium in ODZs waters are only on the order of tens to hundreds of nanomolar 13, 44 , indicating that urea can be important for ODZ anammox bacteria when ammonium is limiting. In contrast to cyanate, urease is not widespread in anammox bacteria or the Ca.…”

Low salinity destabilizes the bacterial community of sugar kelp,Saccharina latissima(Phaeophyceae)

“…Seasonal cycling can drive predictable change in environmental [16, 17] and host-associated [18] bacterial communities. Additionally, local abiotic conditions, including salinity, can significantly shape the bacterial community in the water column [19, 20] and on non-kelp algal hosts [21–23]. Temperature and temperature significantly alter the bacterial community of the kelp Ecklonia radiata in the lab [24], but it is not known how salinity influences the bacterial community of kelps.…”