The Utilization of Dissolved Free Amino Acids by Estuarine Microorganisms
The Utilization of Dissolved Free Amino Acids by Estuarine Microorganisms
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河口微生物对溶解游离氨基酸的利用
DOI：
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发表时间：
1974
期刊：
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通讯作者：
K. L. Webb
中科院分区：
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作者：
C. C. Crawford;J. Hobbie;K. L. Webb
通过测定浮游植物对有机物的吸收速率，研究了浮游植物在帕姆利科河口碳循环中的重要性。我们的方法允许与Michaelis-Menten动力学方程的分析，和溶解的游离氨基酸（DFAA）和葡萄糖的吸收率以及随后作为CO2呼吸的碳的百分比进行了测定。此外，使用离子交换色谱法测定水中氨基酸的浓度。其他测试包括测量初级生产力和水中其他氨基酸对一种氨基酸吸收的影响。异养活性随时间和距离的变化很大，可能是由于浮游生物和溶解性化合物在水中的分布不均匀造成的。虽然氨基酸之间存在竞争，但对动力学测量的影响可能可以忽略不计。每3小时进行一次试验，结果表明天冬氨酸最大吸收速度（Vmax）的变异系数（CV）仅为26%，每日样品的CV相似。在几种情况下，发现一种氨基酸的摄取被另一种氨基酸的存在竞争性抑制，但抑制所需的浓度远高于天然浓度，这种影响在自然界中可能并不重要。相似氨基酸对谷氨酸和天冬氨酸、苏氨酸和丝氨酸、甘氨酸和丙氨酸、亮氨酸和丙氨酸之间存在相互抑制作用。最高Vmax值出现在夏季和初秋，范围从8月份丙氨酸的69.42 mg C/1°hr到较冷月份大多数底物的0.20 mg C/1°hr。葡萄糖摄取的Vmax值（0.06至9.64 mg C/1°hr）表明，该河口系统是测试的最具微生物活性的环境之一。DFAA在水中的浓度为10至30 mg C/l;其中一半以上是鸟氨酸、甘氨酸和丝氨酸。DFAA仅占水中溶解有机碳总量的0.2%左右。此外，DFAA浓度的季节变化，一般平行的初级生产力，表明氨基酸来源于藻类排泄和藻类细胞的腐烂。个别氨基酸的丰度和浓度的顺序与其他水体的报告相似。当基质的自然浓度已知时，可以找到该基质的实际吸收速度（Vn）或通量。在最冷的月份，通量率仅为Vmax值的1%-10%;在最热的月份发现最高值。在每个实验浓度的氨基酸中，一定量的氨基酸被吸收，并且该量的一定百分比被氧化成二氧化碳。尽管实验时间、底物浓度和温度不同，但特定氨基酸的百分比是恒定的。亮氨酸的呼吸率最低（13%），而天冬氨酸和谷氨酸的呼吸率最高（50%）。未能纠正这种呼吸损失的摄取数据会导致严重低估。通过用其特征呼吸百分比校正每种氨基酸的总摄取量来计算颗粒物质的产生。超过60%的氨基酸颗粒生产是通过摄取丙氨酸、亮氨酸、缬氨酸、丝氨酸、甘氨酸、天冬氨酸和谷氨酸。该年的颗粒物产量平均为0.79 mg C/1.hr，范围为0. 6至2.37 mg C/1.hr;这大约是夏季藻类生产率的10%。这种数量的颗粒有机物质是这个河口食物链的重要贡献。
The importance of vacteria in the cycling of carbon in the Pamlico River estuary was studied by measuring the rates of uptake of organic compounds. Our methods allowed analysis with the Michaelis—Menten kinetics equations, and both the rates of uptake of dissolved free amino acids (DFAA) and glucose as well as the percentage of carbon subsequently respired as CO2 were determined. In addition, the concentrations of the amino acids in the water were determined using ion exchange chromatography. Other tests included measurements of primary productivity and of the effects of the other amino acids in the water upon the uptake of one amino acid. There was considerable variation in the heterotrophic activity over time and distance probably caused by patchiness in distribution of plankton and dissolved compounds in the water. Although there is some competition between amino acids being taken up, the effect upon kinetics measurements is probably negligible. Tests made every 3 hr showed a coefficient of variability (CV) of the measured maximum velocity of uptake (Vmax) of aspartic acid to be only 26%, and a similar CV was found for daily samples. In several instances the uptake of one amino acid was found to be competitively inhibited by the presence of another amino acid, but the concentrations necessary to inhibit were far above natural concentrations and such effects are probably unimportant in nature. Mutual inhibition was found between the similar amino acid pairs glutamic acid and aspartic acid, threonine and serine, glycine and alanine, and leucine and alanine. Highest Vmax values were found during the summer months and early fall and ranged from a high of 69.42 mg C/1°hr for alanine in August to less than 0.20 mg C/1°hr for most of the substrates tested in the colder months. The Vmax values for glucose uptake (0.06 to 9.64 mg C/1°hr) indicate that this estuarine system is one of the most microbially—active environments tested. The DFAA were presented in the water at concentrations of from 10 to 30 mg C/1; over half of this was ornithine, glycine, and serine. The DFAA were only about 0.2% of the total dissolved organic carbon in the water. Further, seasonal variations of DFAA concentrations, generally paralleling those of primary productivity, suggested that the amino acids originated from algal excretion and the decay of algal cells. The orders of abundance and concentrations of individual amino acids were similar to those reported for other bodies of water. When the natural concentration of a substrate is known the actual velocity of uptake (Vn) or flux for that substrate may be found. Flux rates were only 1%—10% of the Vmax values in the coldest months; the highest values were found in the warmest months. At each experimental concentration of amino acid, a certain amount was taken up, and a percentage of this amount was oxidized to caron dioxide. This percentage was constant for a particular amino acid in spite of varying experimental times, substrate concentrations, and temperatures. Leucine had the lowest percent respired (13%) while aspartic and glutanic acids had the highest (50%). Failure to correct uptake data for this respiratory loss introduces significant underestimation. The production of particulate material was calculated by correcting total uptake figures for each amino acid by its characteristic respiration percentage. Over 60% of the particulate production from amino acids was by uptake of alanine, leucine, valine, serine, glycine, aspartic acid, and glutamic acid. Such particulate production averaged 0.79 mg C/1.hr for the year and ranged from 0..6 to 2.37 mg C/1.hr; this is about 10% of the rate of production by algae during the summer months. This amount of particulate organic material is a significant contribution to this estuarine food chain.