[A-CG46] 海洋表層－大気間の生物地球化学

[ACG46-P04] 海洋細菌による揮発性有機化合物の生成に関する実験的解析

*大森 裕子¹、髙橋 俊輝²、濱 健夫³、猪俣 敏⁴、谷本 浩志⁴ (1.筑波大学 生命環境系、2.筑波大学大学院　生命環境科学研究科、3.獨協大学　経済学部、4.国立環境研究所　地球システム領域)

キーワード：揮発性有機化合物、硫化ジメチル、アセトン、バクテリア、海洋―大気相互作用

Volatile organic compounds (VOCs), such as dimethyl sulfide (DMS) and acetone, affect particle formation and oxidation capacity in the atmosphere. The ocean is a sink and source of these VOCs, and their dynamics in the surface ocean influences their distribution in the atmosphere. Marine microorganisms, such as phytoplankton and bacteria, are involved in the production and degradation of VOCs in the ocean. Marine bacteria are known to degrade VOCs, but little is known about the production of VOCs by bacteria. In this study, we conducted a bacterial culture experiment using a proton transfer reaction mass spectrometer (PTR-MS) as a detector to comprehensively examine VOCs produced by marine bacteria. Natural bacterial communities in surface seawater collected from Nabeta Bay, Shizuoka Prefecture, were added to artificial seawater and cultured for 10 days. 13C-glucose was used as a substrate, and 13C-labeled VOCs produced by marine bacteria were measured by PTR-MS. At the same time, acetaldehyde-d3 and acetone-d6 were used to measure the degradation rates of acetaldehyde and acetone by marine bacteria. Marine bacteria produced acetaldehyde, acetone, and four types of sulfur-containing VOCs, including methanethiol and DMS, during incubation. Acetaldehyde concentrations increased during the exponential growth phase of the bacteria and then rapidly decreased, suggesting that marine bacteria play a role as producers and degraders of acetaldehyde. Acetone and four sulfur-containing VOCs increased after the stationary phase. These VOCs appeared to be produced as secondary metabolites of bacteria or released upon bacterial lysis. The production rate of acetone was much higher than the degradation rate, suggesting that marine bacteria contribute more to the production of acetone than to its degradation. Our results indicate that marine bacteria are not only degraders of acetaldehyde but also producers of oxygenated and sulfur-containing VOCs. It is also suggested that the growth phase of bacteria is one of the important factors determining the composition and production rate of VOCs.