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 0 N, 123 50.50 0 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.

Incorporating Microbes into Laboratory-Grown Chimneys for Hydrothermal Microbiology Experiments

“…The relatively short duration of these experiments (∼10 h) is also probably a factor, even with different precipitation chemistries. Microbial colonization of a newly formed hydrothermal chimney can occur on reasonable experimental timescales, as shown in an artificial chimney field experiment that showed microbial growth within 92 h; this is in line with hydrothermal microbial doubling times at active vent sites . Thus, for an active chimney experiment, injection timescales of at least several days to a week would probably be optimal.…”

“…In previous lab-grown hydrothermal chimney experiments, the chimney precipitation has taken place over several hours to several days and maintained disequilibrium. ,,,, However, microbial doubling times range greatly from hours to days and are also condition-dependent. For example, bacteria in hydrothermal fluid mixing zones at the Okinawa Trough had estimated doubling times from 21 to 110 h depending on the proximity to active vent sites . To enable such organisms to grow in a laboratory chimney experiment would require careful fine-tuning of the timescales involved in bacterial doubling, chimney growth, and injection durations.…”

“…For example, bacteria in hydrothermal fluid mixing zones at the Okinawa Trough had estimated doubling times from 21 to 110 h depending on the proximity to active vent sites. 76 To enable such organisms to grow in a laboratory chimney experiment would require careful fine-tuning of the timescales involved in bacterial doubling, chimney growth, and injection durations.…”

“…Microbial colonization of a newly formed hydrothermal chimney can occur on reasonable experimental timescales, as shown in an artificial chimney field experiment that showed microbial growth within 92 h; 82 this is in line with hydrothermal microbial doubling times at active vent sites. 76 Thus, for an active chimney experiment, injection timescales of at least several days to a week would probably be optimal. Lab-grown chimneys are interesting since they grow self-organizing mineral structures with complex pore structures and can be formed of redox-active minerals that can provide additional energy parameters to the system, for example, electrically conductive minerals that could support extracellular electron transfer.…”