open access

https://doi.org/10.14943/doctoral.k12415

https://hdl.handle.net/2115/63819

土壌微生物と陸上高等植物代謝物質の大気輸送バイオマーカーとしてのヒドロキシ脂肪酸

英語

2016-09-26

Hokkaido University

185p

Lipid biomarkers have long been employed as a powerful tool to assess therelative significance of soil microorganisms, epicuticular plant waxes and also, to some extent,for characterizing microbial communities in different environmental archives. Among thevarious lipid class compounds, hydroxy fatty acids (FAs) are one such proxy due to theirubiquitous occurrence as an essential membrane component of soil microorganisms andhigher plant waxes. In particular, the positional β-isomers of hydroxy FAs having carbonchain length from C10 to C18 are specific to endotoxin/lipopolysaccharides (LPS) of Gramnegativebacteria (GNB). The long-term exposure to airborne endotoxin can cause severeallergies and infections in human beings. Apart from β-, other positional isomers of hydroxyFAs such as α- and ω-short-chain homologues have the potential to be used as tracers of soilmicroorganisms. However, they are also abundant in microalgae, cyanobacteria, sea grasses,and plant waxes. Moreover, these hydroxy FAs can also act as intermediate products ofphotochemical as well as microbial oxidation of long-chain monocarboxylic acids todicarboxylic acids.Hydroxy FAs from soil microbes and plants can be emitted into the atmospheredue to the wind abrasion during dust events and soil-dust re-suspension during biomassburning (forest fires/agricultural burning). Once in the atmosphere, these hydroxy FAs can betransported to distant places and, thus, can have severe impacts on climate, human health anddownwind ecosystems. The major objectives of my thesis are to better understand the sourceregions, atmospheric transport and deposition of soil- and plant-associated bacteria, and also,higher plant metabolites in the East Asian outflow (Asian dust) to the North Pacific. Toaccomplish these targets, hydroxy FAs were measured in different atmospheric samplesincluding aerosol (urban, coastal, marine), snow (fresh and snow pit) and rain water samplescollected from the East Asian outflow.Results obtained from my thesis contribute to fill-up the gap between thesources of hydroxy FAs and their deposition into fresh water and marine sediments. A clearseasonal trend in the atmospheric abundances of hydroxy FAs over marine (Jeju andChichijima) islands is noteworthy with spring/winter maxima and summer/autumn minima.Furthermore, these seasonal cycles are consistent with the prevailing meteorology. Air massback-trajectories and other soil microbial tracers (such as trehalose) indicate the influence ofAsian dust outbreaks originating from Mongolian and Gobi Deserts and also from China loess plateau during winter and spring. To examine the influence of open biomass burning on soilmicrobes, hydroxy FAs have also been measured in wheat residue combustion derivedaerosols over Mt. Tai, North East China. These analyses have revealed significant emissionsof -hydroxy FAs (tracers of GNB) and endotoxin in high biomass burning events. It has beenalso found that these hydroxy FAs can be removed from the atmosphere efficiently by snowand rain as compared to aerosols.The overall results obtained through my study clearly document the long-rangeatmospheric transport of hydroxy FAs, which are tracers of soil microbes (bacteria, fungi,protozoa) and higher plant waxes, from the Asian continent to the North Pacific. The Asiandust outbreaks in spring can lead to increase in atmospheric abundances of hydroxy FAs and,thereby, resulting in the occurrence of health impacts in downwind regions due to theexposure to these airborne particles. This chemical marker based approach (cultureindependent technique) is a suitable tool for the rapid and comparative analysis of bacterialdry mass and their endotoxin in the various environmental samples which excludes the needof biological recovery and microbial cultivation.

2016-09-26

甲第12415号

博士(環境科学)

(主査) 准教授 関 宰, 特任教授 吉川 久幸, 教授 杉本 敦子, 助教 宮崎 雄三, 教授 河村 公隆 （中部大学中部高等学術研究所）, 教授 鈴木 徳行 （大学院理学研究院）

環境科学院（地球圏科学専攻）

博士論文

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