Summer drought impacts micropredator abundance and microbial food web structure in a rewetted fen peatland

Summer drought significantly affects soil microbiome diversity and functioning, and metabolic interactions in wetland ecosystems, yet its effects on the microbial food web are less understood. We investigated the dynamics of bacterivorous microorganisms and prey bacteria in a rewetted fen peatland before, during, and after a summer drought using small subunit ribosomal RNA (SSU rRNA) gene sequencing and quantitative metatranscriptomics. We identified bacterivores including bacteria (e.g. Myxobacteria), protists, and nematodes, as well as Ca. Patescibacteria and DPANN archaea (PD) having a host-dependent lifestyle. In addition, bacteriophage transcripts were enumerated. The summer drought increased the diversity of bacterivorous protists and bacteria in the fen, along with decreases in water level and increases in redox potential. The SSU rRNA transcripts abundances for all bacterivores (with the exception of PD) increased during drought, reaching a peak in October. The transcript abundance of all bacterivores remained above pre-drought level for at least four months after the drought end. This became more evident when assessing the bacterivore-to-prey bacteria ratios, with the ratios of aerobic bacterivorous bacteria, protists, nematode to prey bacteria increasing by more than two-fold compared to pre-drought. In contrast, PD and bacteriophage-to-prey ratios remained rather stable. This study provides a holistic view of diversity and composition of bacterivores in a fen peat microbiome, including PD and bacteriophages, and suggests a long-lasting impact of summer drought on bacterivore and food web dynamics. The strong responses of aerobic bacterivores may lead to changes in ecosystem functioning through modulated trophic interactions in a changing climate.