Tadonléké R D, Planas D, Lucotte M
GEOTOP, Université du Québec à Montréal, C.P. 8888, Succ. Centre ville, Montréal, Québec, H3C 3P8, Canada.
Microb Ecol. 2005 Feb;49(2):325-41. doi: 10.1007/s00248-004-0232-2. Epub 2005 Jun 17.
In order to assess the factors that determine the dynamics of bacteria with high nucleic acid content in aquatic systems, we (i) conducted 24-h in situ dialysis experiments, involving different fractions of plankton and unfiltered water and (ii) examined empirical relationships between bacteria and both abiotic factors and protists, in boreal humic freshwaters (reservoir and lakes) in the James Bay region (Québec, Canada). Bacteria were subdivided into two subgroups on the basis of their nucleic acid content assessed by flow cytometry. The abundance of bacteria with the highest nucleic acid content and high light scatter (HNA-hs) was significantly correlated, across sites, to bacterial production, whereas bacteria with lower nucleic acid content (LNA) and total bacteria were not. In addition, HNA-hs growth was higher and more variable than LNA growth, indicating that HNA-hs were the most dynamic bacteria. Heterotrophic nanoflagellate and ciliate biomass represented, on average, 5 and 13% of bacterial biomass, respectively. Both in ambient waters and in experiments, ciliates were significantly and negatively correlated with bacteria, whereas heterotrophic nanoflagellates, likely under the grazing pressure from ciliates and metazooplankton, were not. Among ciliates, Cyclidium glaucoma appeared to play an important role. Its growth was significantly and negatively correlated to that of HNA-hs but not to that of LNA. In ambient waters, the abundance of this species explained 56% of the variations in HNA-hs abundance and only 27% of those for LNA. The abundances of total bacteria and LNA significantly increased with chlorophyll a, whereas those of HNA-hs did not. In addition, during the experiments, the estimated potential losses of HNA-hs significantly increased with the initial abundance of C. glaucoma. These results suggest selective removal of the most dynamic bacteria by C. glaucoma and indicate that ciliates may play an important role in the dynamics of active bacteria in natural waters. These findings suggest the existence, within the aquatic microbial food webs, of keystone species that are very important in regulating the activity structure of bacteria.
为了评估决定水生系统中高核酸含量细菌动态变化的因素，我们（i）在加拿大魁北克省詹姆斯湾地区的北方腐殖质淡水（水库和湖泊）中进行了24小时原位透析实验，实验涉及浮游生物的不同组分和未过滤的水，并且（ii）研究了细菌与非生物因素以及原生生物之间的经验关系。通过流式细胞术评估细菌的核酸含量，并将细菌分为两个亚组。在各个位点，核酸含量最高且光散射高（HNA-hs）的细菌丰度与细菌生产显著相关，而核酸含量较低的细菌（LNA）和总细菌则不然。此外，HNA-hs的生长高于且比LNA的生长更具变异性，这表明HNA-hs是最具活力的细菌。异养型纳米鞭毛虫和纤毛虫生物量分别平均占细菌生物量的5%和13%。在环境水体和实验中，纤毛虫均与细菌呈显著负相关，而异养型纳米鞭毛虫可能在来自纤毛虫和后生浮游动物的捕食压力下，与细菌无显著相关性。在纤毛虫中，青光眼环虫似乎起着重要作用。它的生长与HNA-hs的生长显著负相关，但与LNA的生长无关。在环境水体中，该物种的丰度解释了HNA-hs丰度变化的56%，而对LNA丰度变化的解释仅为27%。总细菌和LNA的丰度随叶绿素a显著增加，而HNA-hs的丰度则不然。此外，在实验过程中，HNA-hs的估计潜在损失随青光眼环虫的初始丰度显著增加。这些结果表明青光眼环虫对最具活力的细菌有选择性清除作用，并表明纤毛虫可能在天然水体中活性细菌的动态变化中发挥重要作用。这些发现表明，在水生微生物食物网中存在关键物种，它们在调节细菌的活性结构方面非常重要。
