Quantification of microbial communities in hydrothermal vent habitats of the southern mariana trough and the mid-okinawa trough

The structure of microbial populations near chemosynthetic faunal communities of two geographically and geologically distinct deep-sea hydrothermal vent fields were quantitatively evaluated using catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). The hydrothermal vent of the Southern Mariana Trough (SMT) was dominated by colonization of gastropods in the low-temperature diffuse hydrothermal fluid, whereas macrofauna in mixing zones of the Mid-Okinawa Trough (MOT) consisted of polychaetes, galatheid crabs, and bivalves. A quantitative comparison revealed that the microbial community of the SMT hydrothermal vent field is significantly different from that of the MOT and is strongly influenced by mixing conditions between reduced hydrothermal fluid and oxygenated seawater. In particular, a high proportion of Epsilonproteobacteria was found in the SMT hydrothermal fluid, which is composed of approximately 88% seawater. In contrast, sulfur oxidizers in Gammaproteobacteria were most abundant near vent fauna habitats in the MOT. Our results suggest that the SMT hydrothermal environment is distinct from that of the MOT and affects the community structure of macrofauna and microbial flora.