Chauhan Ashvini, Cherrier Jennifer, Williams Henry N
Environmental Sciences Institute, Florida A&M University, Frederick S. Humphries Science Research Building, Suite 305-D, Tallahassee, FL 32307, USA.
Proc Natl Acad Sci U S A. 2009 Mar 17;106(11):4301-6. doi: 10.1073/pnas.0809671106. Epub 2009 Feb 27.
In aquatic systems, bacterial community succession is a function of top-down and bottom-up factors, but little information exists on "sideways" controls, such as bacterial predation by Bdellovibrio-like organisms (BLOs), which likely impacts nutrient cycling within the microbial loop and eventual export to higher trophic groups. Here we report transient response of estuarine microbiota and BLO spp. to tidal-associated dissolved organic matter supply in a river-dominated estuary, Apalachicola Bay, Florida. Both dissolved organic carbon and dissolved organic nitrogen concentrations oscillated over the course of the tidal cycle with relatively higher concentrations observed at low tide. Concurrent with the shift in dissolved organic matter (DOM) supply at low tide, a synchronous increase in numbers of bacteria and predatorial BLOs were observed. PCR-restriction fragment length polymorphism of small subunit rDNA, cloning, and sequence analyses revealed distinct shifts such that, at low tide, significantly higher phylotype abundances were observed from gamma-Proteobacteria, delta-Proteobacteria, Bacteroidetes, and high G+C gram-positive bacteria. Conversely, diversity of alpha-Proteobacteria, beta-Proteobacteria, and Chlamydiales-Verrucomicrobia group increased at high tides. To identify metabolically active BLO guilds, tidal microcosms were spiked with six (13)C-labeled bacteria as potential prey and studied using an adaptation of stable isotope probing. At low tide, representative of higher DOM and increased prey but lower salinity, BLO community also shifted such that mesohaline clusters I and VI were more active; with an increased salinity at high tide, halotolerant clusters III, V, and X were predominant. Eventually, (13)C label was identified from higher micropredators, indicating that trophic interactions within the estuarine microbial food web are potentially far more complex than previously thought.
在水生系统中，细菌群落演替是自上而下和自下而上因素作用的结果，但关于“侧向”控制的信息却很少，比如类蛭弧菌属生物（BLOs）对细菌的捕食作用，这种捕食作用可能会影响微生物环内的养分循环以及最终向更高营养级的输出。在此，我们报告了佛罗里达州阿巴拉契科拉湾这个以河流为主的河口地区，河口微生物群和BLO物种对潮汐相关溶解有机物供应的瞬态响应。溶解有机碳和溶解有机氮浓度在潮汐周期中呈振荡变化，在低潮时观测到的浓度相对较高。随着低潮时溶解有机物（DOM）供应的变化，同时观察到细菌和捕食性BLO数量同步增加。小亚基rDNA的PCR-限制性片段长度多态性分析、克隆及序列分析揭示了明显的变化，即在低潮时，γ-变形菌纲、δ-变形菌纲、拟杆菌门和高G+C革兰氏阳性菌的系统发育型丰度显著更高。相反，α-变形菌纲、β-变形菌纲和衣原体-疣微菌菌群的多样性在高潮时增加。为了识别具有代谢活性的BLO群落，在潮汐微宇宙中加入六种¹³C标记的细菌作为潜在猎物，并采用稳定同位素探测的改进方法进行研究。在低潮时，代表着较高DOM、更多猎物但盐度较低的环境，BLO群落也发生了变化，使得中盐度簇I和VI更为活跃；在高潮时盐度增加，耐盐簇III、V和X占主导地位。最终，在更高营养级的捕食者中鉴定出了¹³C标记，这表明河口微生物食物网内的营养相互作用可能比之前认为的要复杂得多。
