Biology subjects

Holliger, C.

Publications and source records attributed to Holliger, C..

4 recordsLinked to original sources

bioRxiv2026

From dynamic transcripts to stable proteins: multi-omics revealed regulatory buffering of Candidatus Accumulibacter under cyclic conditions

Enhanced biological phosphorus removal (EBPR) relies on polyphosphate-accumulating organisms that experience dynamic fluctuations in redox conditions and substrate availability. How these organisms regulate metabolism across molecular layers under cyclic operation remains incompletely understood. Here, we investigated molecular regulation in a long-term, stable aerobic granular sludge system dominated by Candidatus Accumulibacter. We combined metagenomics, time-resolved metatranscriptomics, and matched metaproteomics across three consecutive operational cycles. Genome-resolved metagenomics revealed an Accumulibacter-dominated community encoding canonical EBPR functions. Time-resolved metatranscriptomics revealed extensive and reproducible transcriptional dynamics affecting hundreds of genes. These dynamics did not align with discrete EBPR phases or instantaneous environmental transitions, but instead unfolded gradually over the cycle. Despite pronounced transcript-level heterogeneity, aggregation at the functional level revealed strong consolidation, with only a limited number of KEGG orthologs exhibiting coherent temporal regulation. Quantitative metaproteomics revealed a stable proteome across EBPR cycles, with no individual proteins or functional categories showing significant differential abundance despite direct transcript-protein mapping and time-matched sampling. This indicated that transcriptional dynamics did not translate into measurable changes in protein pool size on the time scale of individual cycles, consistent with slow, growth-coupled proteome turnover relative to cycle duration. Together, these results support a hierarchical model of regulation in Candidatus Accumulibacter, in which dynamic transcriptional responses are buffered at both the functional and protein levels. This organization provides a plausible basis for stable EBPR performance under predictable cyclic operation and demonstrates how time-resolved multi-omics can be used to resolve regulatory dynamics across molecular layers in engineered microbial ecosystems.

microbiology↗

bioRxiv2024

Multiple extracellular polymeric substances pathways expressed by Accumulibacter and the flanking community during aerobic granule formation and after influent modification

Aerobic granular sludge is a biological wastewater treatment process in which a microbial community forms a granular biofilm. The role of Candidatus Accumulibacter in the production of a biofilm matrix composed of extracellular polymeric substances was studied in a sequencing batch reactor enriched with polyphosphate-accumulating organisms. The metabolisms of the microbial populations were investigated using de novo metatranscriptomics analysis. Finally, the effect of decreasing the influent phosphate concentration was investigated. A few weeks after the reactor start-up, the microbial community was dominated by Accumulibacter. Up to nine species were active in parallel. However, the most active species differed according to sampling time. Reducing the phosphate concentration led to a dominance of the glycogen-accumulating organism Propionivibrio, with some Accumulibacter species still abundant. De novo metatranscriptomic analysis indicated a high diversity of potential extracellular substances produced mainly by Azonexus, Accumulibacter, Candidatus Contendobacter, and Propionivibrio. Moreover, the results suggest that Azonexus, Contendobacter and Propionivibrio recycle the neuraminic acid produced by Accumulibacter. Changes in the microbial community did not cause the granules to disintegrate, indicating that a Propionivibrio-dominated community can maintain stable granules.

microbiology↗

bioRxiv2023

Structure of a membrane-bound menaquinol:organohalide oxidoreductase

Organohalide-respiring bacteria are key organisms for the bioremediation of soils and aquifers contaminated with halogenated organic compounds. The major players in this process are respiratory reductive dehalogenases, corrinoid enzymes that use organohalides as substrates and contribute to energy conservation. Here, we present the first structure of a functional menaquinol:organohalide oxidoreductase (MOOR) obtained by cryo-EM. The membrane-bound protein was isolated from Desulfitobacterium hafniense strain TCE1 as a PceA2B2 complex catalysing the dechlorination of tetrachloroethene (PCE). Two catalytic PceA subunits are anchored to the membrane by two small integral membrane PceB subunits. The structure reveals two menaquinone molecules bound at the interface of the two different subunits, which are the starting point of a chain of redox cofactors for electron transfer to the active site. This structure elucidates how energy is conserved during organohalide respiration in menaquinone-dependent organohalide-respiring bacteria.

microbiology↗

bioRxiv2018

Strain-level diversity drives alternative community types in millimeter scale granular biofilms

Microbial communities are often highly diverse in their composition, both at the level of coarse-grained taxa such as genera as well as at the level of strains within species. This variability can be driven by both extrinsic factors like temperature, pH, etc., as well as by intrinsic ones, such as demographic fluctuations or ecological interactions. The relative contributions of these factors and the taxonomic level at which they influence community structure remain poorly understood, in part because of the difficulty of identifying true community replicates assembled under the same environmental parameters. Here, we address this problem using an activated granular sludge reactor in which millimeter scale biofilm granules represent true community replicates whose differences in composition are expected to be driven primarily by biotic factors. Using 142 shotgun metagenomes of single biofilm granules we found that, at the commonly used genuslevel resolution, community replicates varied much more in their composition than would be expected from neutral assembly processes. This variation, however, did not translate into any clear partitioning into discrete community types, i.e. the equivalent of enterotypes in the human gut. However, a strong partition into community types did emerge at the strain level for the most abundant organism: strains of Candidatus Accumulibacter that coexisted in the metacommunity--i.e. the reactor--excluded each other within community replicates. Single-granule communities maintained a significant lineage structure, whereby the strain phylogeny of Accumulibacter correlated with the overall species composition of the community, indicating high potential for co-diversification among species and communities. Our results suggest that due to the high functional redundancy and competition between close relatives, alternative community types are most likely observed at the level of recently differentiated genotypes but not higher orders of genetic resolution.

microbiology↗