National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan.
Appl Environ Microbiol. 2013 Dec;79(23):7160-8. doi: 10.1128/AEM.01504-13. Epub 2013 Sep 13.
Incubation experiments using filtered waters from Lake Kasumigaura were conducted to examine bacterial contribution to a dissolved organic carbon (DOC) pool. Bacterial abundance, bacterial production, concentrations of DOC, total dissolved amino acids (TDAA), and total dissolved neutral sugars (TDNS) were monitored during the experiments. Bacterial production during the first few days was very high (20 to 35 μg C liter(-1) day(-1)), accounting for 40 to 70% of primary production. The total bacterial production accounted for 34 to 55% of the DOC loss during the experiment, indicating high bacterial activities in Lake Kasumigaura. The DOC degradation was only 12 to 15%, whereas the degradation of TDAA and TDNS ranged from 30 to 50%, suggesting the preferential usage of TDAA and TDNS. The contribution of bacterially derived carbon to a DOC pool in Lake Kasumigaura was estimated using d-amino acids as bacterial biomarkers and accounted for 30 to 50% of the lake DOC. These values were much higher than those estimated for the open ocean (20 to 30%). The ratio of bacterially derived carbon to bulk carbon increased slightly with time, suggesting that the bacterially derived carbon is more resistant to microbial degradation than bulk carbon. This is the first study to estimate the bacterial contribution to a DOC pool in freshwater environments. These results indicate that bacteria play even more important roles in carbon cycles in freshwater environments than in open oceans and also suggests that recent increases in recalcitrant DOC in various lakes could be attributed to bacterially derived carbon. The potential differences in bacterial contributions to dissolved organic matter (DOM) between freshwater and marine environments are discussed.
利用从霞浦湖过滤得到的水进行了孵育实验，以研究细菌对溶解有机碳 (DOC) 库的贡献。在实验过程中监测了细菌丰度、细菌生产力、DOC 浓度、总溶解氨基酸 (TDAA) 和总溶解中性糖 (TDNS) 的浓度。在最初几天，细菌生产力非常高（20 到 35 μg C 升(-1) 天(-1)），占初级生产力的 40 到 70%。总细菌生产力占实验过程中 DOC 损失的 34 到 55%，表明霞浦湖中细菌活性很高。DOC 的降解仅为 12 到 15%，而 TDAA 和 TDNS 的降解范围为 30 到 50%，表明 TDAA 和 TDNS 的优先利用。利用 d-氨基酸作为细菌生物标志物，估算了霞浦湖中细菌衍生碳对 DOC 库的贡献，占湖 DOC 的 30 到 50%。这些值远高于开阔海洋中的估计值（20 到 30%）。细菌衍生碳与总碳的比值随时间略有增加，表明细菌衍生碳比总碳更能抵抗微生物降解。这是首次在淡水环境中估算细菌对 DOC 库的贡献。这些结果表明，细菌在淡水环境中的碳循环中发挥的作用比开阔海洋中更为重要，也表明最近各种湖泊中难降解 DOC 的增加可能归因于细菌衍生碳。讨论了淡水和海洋环境中细菌对溶解有机物 (DOM) 贡献的潜在差异。
