Production process of refractory marine dissolved organic matter by marine bacteria ; Experimental analyses using bacteria-specific D-amino acids.

本研究旨在阐明海洋溶解有机物(DOM)，特别是难溶组分(R-DOM)产生的生物地球化学过程，探讨DOM和/或R-DOM作为地球有机碳库的意义及其与全球碳变化和循环的可能关系。采用~(13)C示踪剂、GC和GC/MS相结合的方法，通过示踪培养样品中溶解有机成分，特别是细菌特有的D-氨基酸的浓度和组成，分析了海洋细菌对DOM产生，特别是对R-DOM产生的贡献。然后将该溶液在27℃的黑暗中孵育90天以上。在Interva…处回收等份样品培养初期(1~4天)，DOC浓度及其初始浓度(^&lt；13&gt；C/^&gt；12&gt；C/^&lt；13&gt；C/^&lt；12&gt；C/^&lt；13&gt；C/^&lt；12&gt；C/^&lt；12&gt；C/^&lt；13&gt；12&gt；C/^&lt；13&gt；12&gt；C/^&lt；13&gt；13&gt；C/^&lt；13&gt；C-ATOM%)严格降低，表明细菌最有可能将~-C-葡萄糖转化(和/或消耗)为其他有机分子和CO_2。结果表明，13&gt；13&gt；13&gt；C-氨基酸和D-氨基酸，特别是^&lt；13&gt；C-丙氨酸和D-，L-丙氨酸是细菌在培养过程中所特有的。研究还表明，在孵化早期(长达4天)产生的C-DOC和D-丙氨酸，即使在孵化90天后仍保持稳定。2004年，在黑暗中培养60d后，初步由浮游植物光合作用产生的有机碳中约有5%保持稳定，由DOC组成，占所有剩余有机碳的60%以上，具有相对低的相对分子质量和更难生物降解的性质。由此可见，海洋R-DOM的大部分是由海洋细菌通过其对浮游植物光合作用产物的特异性转化而产生的。考虑到全球碳变化和再循环的环境重要性，还应能够估计细菌对R-DOM生产的贡献作为碳隔离的函数的大小。较少

Subjects in this study were to clear the biogeochemical process of production of marine dissolved organic matter(DOM), particularly that of refractory fraction(R-DOM), and to discuss the significance of DOM and /or R-DOM as an organic carbon reservoir on earth and its possible relation to global carbon change and recycle. An incubation experiment was carried out for the analyses of contribution of marine bacteria to DOM production, especially to R-DOM production, by tracing concentrations and composition of dissolved organic constituents, particularly those of bacteria-specific D-amino acids in culture samples, using combined methods of ^<13>C-tracer, GC, and GC/MS.Glucose(20mgC) labeled with ^<13>C and seawater(2l) of Tokyo Bay containing natural bacterial populations were added as a substrate and bacterial seeds to artificial seawater(18l) in polycarbonate bottle(20l). And then the solution was incubated for over 90days in the dark at 27℃. Aliquots of sample were recovered at interva … More ls 1-30days and filtered through a glass-fiber filter (Whatman, GF/F) so as to apply the filtrate to chemical analysis of DOM.Rapid increasing in concentration of dissolved amino acids, especially of alanine, and high values in ratio of D-alanine to L-alanine were found in early stage(1-4days) of incubation while the concentration of DOC and its initial ^<13>C/^<12>C ratio(^<13>C-atom%) strictly decreased, indicating most probable conversion (and/or consumption) of ^<13>C-glucose to other organic molecules and CO_2 by bacteria. It was obvious that DO^<13>C, ^<13>C-amino acids and D-amino acids, particularly ^<13>C-alanine and D-,L-alanine, were specifically produced by bacteria from ^<13>C-glucose during incubation. It was also revealed that no less than 1% of ^<13>C-DOC and D-alanine produced in early stage of incubation(up to 4days) remained stable even after 90days incubation, respectively.In previous study of Hama et al. 2004, about 5% of organic carbon produced initially by phytoplankton photosynthesis was observed to remain stable after 60days incubation in the dark, which was consisted of DOC and accounted for more over 60% of all organic carbon remained, having a relatively low molecular weight and more biorefractory natures.Form these results, it is obviously shown that major parts of marine R-DOM are produced by marine bacteria through their specific conversion from photosynthetic products of phytoplankton. It should be also enable to estimate a magnitude of contribution of bacteria to R-DOM production as a function of carbon isolation in concerning with the environmental importance of global carbon change and recycle. Less