Distribution of Nitrogen-fixing Bacteria in the Central Pacific Ocean

概要

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The plate culture method using the two formulae for non-nitrogenous media was adopted in this investigation for the purpose of counting and isolating nitrogen-fixing bacteria distributed in the open sea. Sea water samples were collected at eighteen different stationsin the region of Lat. 50°N-15°S along Long. 155°W and two other stations in the Pacific Ocean. In order to compare with those samples from the open sea, water samples were also obtained at four stations in Suruga and Sagami Bays. Nitrogen-fixing bacteria appear to be widely but very unevenly distributed at all depths in sea water, in numbers approximately ranging from nil to 104per 100 mlof sea water, and denser vertical populations have been found in the area of Lat. 40°N and 5°N along Long. 155°W, even at depths from 2, 000 to 3, 000m. A comparatively denser population of bacteriawas found in sea water from Suruga Bay and Sagami Bay. The bacteria associated with plankton were abundantly demonstrated, in numbers ranging from 106to 108per 1 mlsettling volume of plankton, in many plankton samples collected at fourstations in the southern parts of the Pacific Ocean. Almost all the bacteria isolated fromthe samples of blue green algal colonies, Trichodesmiumsp., were able to grow on nonnitrogeneous media.
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