Michelou Vanessa K, Cottrell Matthew T, Kirchman David L
College of Marine and Earth Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958, USA.
Appl Environ Microbiol. 2007 Sep;73(17):5539-46. doi: 10.1128/AEM.00212-07. Epub 2007 Jul 13.
We examined the contribution of photoheterotrophic microbes--those capable of light-mediated assimilation of organic compounds--to bacterial production and amino acid assimilation along a transect from Florida to Iceland from 28 May to 9 July 2005. Bacterial production (leucine incorporation at a 20 nM final concentration) was on average 30% higher in light than in dark-incubated samples, but the effect varied greatly (3% to 60%). To further characterize this light effect, we examined the abundance of potential photoheterotrophs and measured their contribution to bacterial production and amino acid assimilation (0.5 nM addition) using flow cytometry. Prochlorococcus and Synechococcus were abundant in surface waters where light-dependent leucine incorporation was observed, whereas aerobic anoxygenic phototrophic bacteria were abundant but did not correlate with the light effect. The per-cell assimilation rates of Prochlorococcus and Synechococcus were comparable to or higher than those of other prokaryotes, especially in the light. Picoeukaryotes also took up leucine (20 nM) and other amino acids (0.5 nM), but rates normalized to biovolume were much lower than those of prokaryotes. Prochlorococcus was responsible for 80% of light-stimulated bacterial production and amino acid assimilation in surface waters south of the Azores, while Synechococcus accounted for on average 12% of total assimilation. However, nearly 40% of the light-stimulated leucine assimilation was not accounted for by these groups, suggesting that assimilation by other microbes is also affected by light. Our results clarify the contribution of cyanobacteria to photoheterotrophy and highlight the potential role of other photoheterotrophs in biomass production and dissolved-organic-matter assimilation.
2005年5月28日至7月9日，我们沿着从佛罗里达州到冰岛的断面，研究了光能异养微生物（即那些能够通过光介导同化有机化合物的微生物）对细菌生产和氨基酸同化的贡献。细菌生产（终浓度为20 nM时的亮氨酸掺入量）在光照下的样本中平均比黑暗培养的样本高30%，但这种效应差异很大（3%至60%）。为了进一步描述这种光照效应，我们检测了潜在光能异养微生物的丰度，并使用流式细胞术测量了它们对细菌生产和氨基酸同化（添加0.5 nM）的贡献。原绿球藻和聚球藻在观察到光依赖亮氨酸掺入的表层水中数量丰富，而需氧不产氧光合细菌数量丰富，但与光照效应无关。原绿球藻和聚球藻的单细胞同化率与其他原核生物相当或更高，尤其是在光照条件下。微微型真核生物也摄取亮氨酸（20 nM）和其他氨基酸（0.5 nM），但按生物体积归一化后的速率远低于原核生物。在亚速尔群岛以南的表层水中，原绿球藻占光照刺激的细菌生产和氨基酸同化的80%，而聚球藻平均占总同化量的12%。然而，这些群体并未解释近40%的光照刺激亮氨酸同化，这表明其他微生物的同化也受光照影响。我们的结果阐明了蓝细菌对光能异养的贡献，并突出了其他光能异养微生物在生物量生产和溶解有机物同化中的潜在作用。
