Fig. 1

Chemocline of  Kebrit Deep BSI and associated Campylobacterota diversity. A Map of the Red Sea indicating the location of known DHABs (blue circles) and the sampled Kebrit Deep (red circle). B Schematic representation of Kebrit Deep DHAB, including seawater, brine-seawater interface (BSI) and brine body. Niskin bottles are reported to indicate the samples collected in these three portions. While water enclosed in the Niskin bottles from seawater and brine body are used to collect the samples as they are, the selected Niskin bottle enclosing the BSI gradient (see Additional file Figs. S1 and S2) is used to obtain 10 cm water layers (~1 L) in sterile bottles for a total of nine fractions (K1-K9). C CTD profiles of salinity (PSU) and oxygen (mg/L)  at different depths measured during the sampling cast. D The relative abundance of the three MAGs identified as Sulfurimonas (Kbt_01) and Sulfurovum (Kbt_02 and Kbt_03) was computed by mapping the metagenomic sequences back to the MAGs using BBMap. Relative abundance (x-axis) is reported as a percentage (%) for each sample (y-axis), encompassing one seawater (41 PSU), nine BSI layers (K1-K9, 91–155 PSU) and one brine body (218 PSU). Taxonomy was reported following NCBI nomenclature