Abundance and growth rate of bacterioplankton community in hydrothermal vent plumes of the North Fiji Basin

Abstract

Microbiological investigation at the spreading center of the rift system of the North Fiji Basin showed a population density of bacterioplankters in the order of 10 3 cells ml −1, either in plumes of hydrothermal vents or immediately above; about half of these populations were composed of ultramicrocells. Other cells of the bacterioplankton communities were mostly rods in dividing stages. About 20% of the total growing bacterial cells (direct counts) were chemosynthetic (viable counts) in the plumes, whereas more than 99.9%were heterotrophic in the layers immediately above the plumes. The dividing bacterial populations in the plumes were made up of both psychrophiles and mesophiles, and their in situ generation times were estimated to be a few hours to a few days by the frequency of dividing cells method.