ABSTRACT: Despite the importance of bacterial cell volume in microbial ecology in aquatic environments, literature regarding the effects of seasonal and spatial variations on bacterial cell volume remains scarce. We used transmission electron microscopy to examine seasonal and spatial variations in bacterial cell size for 18 mo in 2 layers (epilimnion 0.5 m and hypolimnion 60 m) of Lake Biwa, Japan, a large and deep freshwater lake. During the stratified period, we found that the bacterial cell volume in the hypolimnion ranged from 0.017 to 0.12 µm³ (median), whereas that in the epilimnion was less variable (0.016 to 0.033 µm³, median) and much lower than that in the hypolimnion. Additionally, in the hypolimnion, cell volume during the stratified period was greater than that during the mixing period (up to 5.7-fold). These differences in cell volume resulted in comparable bacterial biomass in the hypolimnion and epilimnion, despite the fact that there was lower bacterial abundance in the hypolimnion than in the epilimnion. We also found that the biomass of larger bacteria, which are not likely to be grazed by heterotrophic nanoflagellates, increased in the hypolimnion during the stratified period. Our data suggest that estimation of carbon flux (e.g. bacterial productivity) needs to be interpreted cautiously when cell volume is used as a constant parametric value. In deep freshwater lakes, a difference in cell volume with seasonal and spatial variation may largely affect estimations.

中文翻译：

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大型淡水湖中大型细菌对细菌生物量的贡献（日本琵琶湖）

摘要：尽管在水生环境中细菌细胞体积在微生物生态学中很重要，但是关于季节性和空间变化对细菌细胞体积的影响的文献仍然很少。我们使用透射电子显微镜检查了日本琵琶湖（一个宽而深的淡水湖）的2层（上浮膜0.5 m和下膜膜60 m）中18 mo的细菌细胞大小的季节性和空间变化。在分层期间，我们发现次lim虫的细菌细胞体积范围为0.017至0.12 µm ³（中值），而上lim虫的细菌细胞体积变化较小（0.016至0.033 µm ³，中位数），远低于次卧层。另外，在次层期中，分层期间的细胞体积大于混合期间的细胞体积（最多5.7倍）。这些细胞体积上的差异导致了下纤毛和上纤毛中可比的细菌生物量，尽管事实上，下纤毛中的细菌丰度比上纤毛中的细菌丰度低。我们还发现，较大细菌的生物量（可能不被异养纳米鞭毛放牧）在分层期间的次生时间增加。我们的数据表明，当细胞体积用作恒定参数值时，需要谨慎解释碳通量（例如细菌生产力）的估算。在深水湖泊中，