Almeida M.A., Cunha M.A., Alcântara F.
Departamento de Biologia, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
Microb Ecol. 2001 Dec;42(4):562-571. doi: 10.1007/s00248-001-0020-1.
The bacterioplankton density in Ria de Aveiro, a shallow estuarine ecosystem, varied in the broad range of 1.9-10.6 x 109 cells L-1. The range of values was about 2 times higher in brackish water than in marine water. At high tide bacterial abundance was 2-3 times lower than at low tide. The overall variation in virioplankton was in the range of 2.4-25.0 x 1010 particles L-1. Brackish water was about 2 times richer in viral particles than the marine water. Near low tide the virioplankton was 2-3 times higher that at high tide. Viral density followed the pattern of bacterial abundance (it explained 40% of virioplankton variation). The viruses to bacterium ratio varied, throughout tidal cycles, by a factor of about 10 establishing the range 4.7-55.6 (average 17.6). This ratio was rather similar in the two estuarine zones. We compared the effects of infection and predation on the control of bacterioplankton size in the two zones of the estuary. The approach to this question was conducted in experimental microcosms, set up in six combinations of plankton variables affecting the presence/absence of predators, virus-to-bacterium ratio (10-fold increase), virus-to-bacterium distance (2.2-fold increase), and bacterial growth rate. The results showed that predation was similar, in a percent basis, in marine (69%) and brackish water (73%). Viral infection was, however, higher in brackish water (59%) than in the marine water (36%). We conclude that the bacterioplankton along the salinity gradient evolves under biological pressures that are in different balance in the marine and brackish water zones. The effect of viral lysis on bacterial communities with enhanced growth (after yeast extract addition) was masked even when the initial ratio was 10-fold greater than in the natural samples. The high density of the virioplankton did not preclude the large and rapid increase in bacterial density. We suggest that the dynamics of the equilibrium between bacteria and viruses in the environment is driven to higher numerical levels during periods of intensive bacterial growth. On the contrary, at low bacterial growth rates the temporarily increased virus-to-bacterium ratio may drive the equilibrium to its lowest levels.
阿威罗里亚（Ria de Aveiro）是一个浅海河口生态系统，其中浮游细菌密度变化范围很大，在1.9 - 10.6×10⁹个细胞/升之间。咸淡水区域的值范围比海水区域高约2倍。涨潮时细菌丰度比落潮时低2 - 3倍。浮游病毒的总体变化范围在2.4 - 25.0×10¹⁰个颗粒/升之间。咸淡水区域的病毒颗粒比海水区域丰富约2倍。接近落潮时浮游病毒比涨潮时高2 - 3倍。病毒密度遵循细菌丰度的模式（它解释了浮游病毒变化的40%）。在整个潮汐周期中，病毒与细菌的比例变化约10倍，范围为4.7 - 55.6（平均17.6）。在河口的两个区域，这个比例相当相似。我们比较了感染和捕食对河口两个区域浮游细菌大小控制的影响。针对这个问题的研究方法是在实验微宇宙中进行的，实验设置了六种浮游生物变量组合，这些变量影响捕食者的存在与否、病毒与细菌的比例（增加10倍）、病毒与细菌的距离（增加2.2倍）以及细菌生长速率。结果表明，从百分比来看，海洋区域（69%）和咸淡水区域（73%）的捕食情况相似。然而，咸淡水区域（59%）的病毒感染高于海水区域（36%）。我们得出结论，沿着盐度梯度的浮游细菌在生物压力下进化，而这种压力在海洋和咸淡水区域的平衡不同。即使初始比例比自然样本高10倍，病毒裂解对生长增强的细菌群落（添加酵母提取物后）的影响也被掩盖了。浮游病毒的高密度并没有阻止细菌密度大量快速增加。我们认为，在细菌大量生长的时期，环境中细菌和病毒之间平衡的动态变化会被驱动到更高的数值水平。相反，在细菌生长速率较低时，暂时增加的病毒与细菌比例可能会将平衡驱动到最低水平。
