Free-living amoebae (FLA) are ubiquitous organisms present in various natural and artificial environments, such as drinking water storage towers (DWST). Some FLA, such as Acanthamoeba sp., Naegleria fowleri, and Balamuthia mandrillaris, can cause severe infections at ocular or cerebral level in addition to being potential reservoirs of other pathogens. In this work, the abundance and diversity of FLA was evaluated in two sampling campaigns: one performed over five seasons in three DWST at three different levels (surface, middle and bottom) in water and biofilm using microscopy and PCR, and one based on the kinetics analysis in phase contrast and confocal microscopy of biofilm samples collected every two weeks during a 3-month period at the surface and at the bottom of a DWST. In the seasonal study, the FLA were detected in each DWST water in densities of ~20 to 25 amoebae L⁻¹. A seasonal variation of amoeba distribution was observed in water samples, with maximal densities in summer at ~30 amoebae L⁻¹ and minimal densities in winter at ~16 amoebae L⁻¹. The FLA belonging to the genus Acanthamoeba were detected in two spring sampling campaigns, suggesting a possible seasonal appearance of this potentially pathogenic amoeba. Interestingly, a 1 log increase of amoebae density was observed in biofilm samples collected at the surface of all DWST compared to the middle and the bottom where FLA were at 0.1–0.2 amoebae/cm². In the kinetics study, an increase of amoebae density, total cell density, and biofilm thickness was observed as a function of time at the surface of the DWST, but not at the bottom. To our knowledge, this study describes for the first time a marked higher FLA density in biofilms collected at upper water levels in DWST, constituting a potential source of pathogenic micro-organisms.

自由生活的变形虫（FLA）是存在于各种自然和人工环境中的无处不在的生物，例如饮用水储存塔（DWST）。一些FLA，例如棘孢菌属（Acanthamoeba sp。），内格尔（Naegleria fowleri）和曼陀罗（Balamuthia mandrillaris）除可能是其他病原体的潜在储存库外，它还可能导致在眼部或脑部严重感染。在这项工作中，FLA的丰度和多样性在两次采样活动中进行了评估：一项使用显微镜和PCR技术在三个DWST中以三种不同水平（表面，中间和底部）在水和生物膜中进行了三个季节的DWST，一项基于在DWST的表面和底部每3周内每两周收集一次的生物膜样品的相差和共聚焦显微镜动力学分析。在季节性研究中，在每种DWST水中以约20至25变形虫L ^-1的密度检测到FLA 。在水样中观察到了变形虫分布的季节变化，夏季最大密度为〜30 amoebae L ^-1和最小密度的冬季在〜16变形虫L ^-1。在两个春季采样活动中检测到了属于棘形棘类的FLA ，这表明这种潜在致病性的变形虫可能出现了季节性出现。有趣的是，相比于FLA处于0.1-0.2 amoebae / cm ²的中部和底部，在所有DWST表面收集的生物膜样品中观察到的amoebae密度增加了1 log。。在动力学研究中，在DWST的表面而非底部发现了变形虫密度，总细胞密度和生物膜厚度随时间的变化。据我们所知，这项研究首次描述了在DWST中较高水位收集的生物膜中明显较高的FLA密度，构成了潜在的病原微生物来源。