In situ determination of bacterial growth in mixing zone of hydrothermal vent field on the hatoma knoll, Southern Okinawa trough

Abstract

The doubling time of indigenous bacteria in mixing-zone of hydrothermal fluid and seawater was determined using a diffusion chamber unit deployed on the field of Hatoma Knoll (24° 51.50′N, 123° 50.50′ E), which is a submarine volcano located on southern Okinawa Trough. The diffusion chamber is a reliable tool to incubate and to directly measure the microbial growth under in situ condition of deep-sea, although an operation of submersible and a complicated preparation of seed water became the technical constraints. The doubling time at non-vent site distant from active vent site was estimated from 86 to 110 h, while at active vent sites more rapid doubling time, 21–32 h, were estimated. A potential sulfur-oxidizing bacteria belonging to Epsilonproteobacteria dominated the population grew in the chambers, which were incubated using the plume water obtained from the mixing zone between the vent fluid and seawater, and Bathymodiolus colony, while no detection of Gammaproteobacteria. The methaneoxidizing bacteria were detected only from gill and digestive tract of Bathymodiolus platifrons, and could not be detected from the chamber, although the chamber was placed on Bathymodiolus colony. The results of this study suggested that chemolithoautotrophic growth near by the hydrothermal vent is sustained by the rapid doubling time of Epsilonproteobacteria using chemical species dissolved in fluid and provides the chemoautotrophic product to deep-sea benthopelagic community, as well as a microbial products in hydrothermal vent plume.