MESOPHILIC SULFATE-REDUCING BACTERIA FROM 3 DEEP-SEA HYDROTHERMAL VENT SITES

The present study was conducted to determine the presence and physiolo gy of mesophilic sulfate-reducing bacteria (SRB) at deep-sea hydrother mal vents, which constitute remote ecosystems, largely dependent on th eir own chemoautotrophic primary production. SRB were enriched and iso lated from samples of hydrothermal water, invertebrates, chimneys, and sediment collected at deep-sea (1700 to 2600 m) hydrothermal vent sit es in the Lau Basin, in the North Fiji Basin, and at 13 degrees N on t he East Pacific Rise. From the hydrothermal fields in the Lau Basin an d the North Fiji Basin, SRB were cultured at 30 degrees C from 19 out of 21 samples, including five samples of high-temperature hydrothermal water (> 100 degrees C). Acetate, benzoate, formate, isobutyrate, and lactate were supplied as single electron donors and could all be degr aded by SRB. From the site at 13 degrees N, SRB were enriched at 20 or 40 degrees C from seven out of 20 samples. Two Desulfovibrio. strains , H 2.5 and H 5.3, originated from the tubes of the polychaete Alvinel la sp. and these strains had optimum temperatures at 37 to 40 degrees C with doubling times of 3.6 and 6.6 hours, respectively. In cultures of strain H 2.5, which had reached the stationary growth phase, almost the entire populations (> 99%) changed into round pleomorphs (coccoid bodies). However, cultures of vibrio-shaped bacteria were recovered u pon transfer of an inoculum to fresh medium. No distinct changes in th e composition of the cell membrane phospholipid fatty acids were assoc iated with the morphological transformation. In the deep-sea hydrother mal vent environment, mesophilic SRB occurred frequently and may thriv e in anoxic habitats in association with warm vent animal communities.