The growth rate is a fundamental characteristic of bacterial species, determining its contributions to the microbial community and carbon flow. High-throughput sequencing can reveal bacterial diversity, but its quantitative inaccuracy precludes estimation of abundances and growth rates from the read numbers. Here, we overcame this limitation by normalizing Illumina-derived amplicon reads using an internal standard: a constant amount of Escherichia coli cells added to samples just before biomass collection. This approach made it possible to reconstruct growth curves for 319 individual OTUs during the grazer-removal experiment conducted in a freshwater reservoir Římov. The high resolution data signalize significant functional heterogeneity inside the commonly investigated bacterial groups. For instance, many Actinobacterial phylotypes, a group considered to harbor slow-growing defense specialists, grew rapidly upon grazers' removal, demonstrating their considerable importance in carbon flow through food webs, while most Verrucomicrobial phylotypes were particle associated. Such differences indicate distinct life strategies and roles in food webs of specific bacterial phylotypes and groups. The impact of grazers on the specific growth rate distributions supports the hypothesis that bacterivory reduces competition and allows existence of diverse bacterial communities. It suggests that the community changes were driven mainly by abundant, fast, or moderately growing, and not by rare fast growing, phylotypes. We believe amplicon read normalization using internal standard (ARNIS) can shed new light on in situ growth dynamics of both abundant and rare bacteria.

Biology Centre CAS Institute of Hydrobiology Na Sádkách 7 37005 Česke Budějovice Czech Republic

Center Algatech Institute of Microbiology CAS Novohradská 237 37981 Třeboň Czech Republic

Center Algatech Institute of Microbiology CAS Novohradská 237 37981 Třeboň Czech Republic Faculty of Science University of South Bohemia in České Budějovice CZ 37005 České Budějovice Czech Republic

Helmholtz Centre for Infection Research 38124 Braunschweig Germany

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