Biology subjects

Hallberg, Z. F.

Publications and source records attributed to Hallberg, Z. F..

5 recordsLinked to original sources

bioRxiv2026

Quenching corrinoid-based interactions in a model bacterial coculture.

Microbial community structure is driven, in part, by the metabolic interdependencies of resident microbes. Thus, manipulating specific metabolic interactions represents one attractive way to both understand how microbial communities perform complex functions and alter them for therapeutic or environmental effects. However, it is not yet possible to control the availability of those metabolites produced by some members of the community that are required by others. Here, we report the development of a metabolite quenching strategy that disrupts a specific metabolic interaction involving corrinoids, the vitamin B12 family of cofactors, by applying a high-affinity corrinoid-binding protein, BtuG, to bacteria engaged corrinoid cross-feeding. Using a model coculture composed of Sinorhizobium meliloti, a bacterium that produces a corrinoid (cobalamin), and an Escherichia coli strain engineered to be corrinoid-dependent, we demonstrate corrinoid quenching by sequestration of extracellular corrinoid and show that BtuG specifically blocks corrinoid-dependent growth. We use this tool to calculate the amount of cobalamin released by S. meliloti cells and find that the cobalamin release rate is dependent on the growth phase of the producer, increasing to a maximum of approximately 40 cobalamin molecules per minute per cell in late exponential phase. This work establishes a strategy to selectively block microbial interactions that may be more broadly applied to dissecting community structure and function. We expect that applying high-affinity molecular sponges to quench nutrient sharing will allow for the identification of key nutrients that structure microbial communities and empower precision microbiome manipulation strategies.

microbiology↗

bioRxiv2024

Vitamin B12 variants structure soil microbial communities despite soil's vast reservoir of B12.

Soil microbial communities perform critical ecosystem services through the collective metabolic activities of numerous individual organisms. Most microbes use corrinoids, a structurally diverse family of cofactors related to vitamin B12. Corrinoid structure influences the growth of individual microbes, yet how these growth responses scale to the community level remains unknown. Analysis of metagenome-assembled genomes suggests corrinoids are supplied to the community by members of the archaeal and bacterial phyla Thermoproteota, Actinobacteria, and Proteobacteria. Corrinoids were found largely adhered to the soil matrix in a grassland soil, at levels exceeding those required by cultured bacteria. Enrichment cultures and soil microcosms seeded with different corrinoids showed distinct shifts in bacterial community composition, supporting the hypothesis that corrinoid structure can shape communities. Environmental context influenced both community and taxon-specific responses to specific corrinoids. These results implicate corrinoids as key determinants of soil microbiome structure and suggest that environmental micronutrient reservoirs promote community stability.

microbiology↗

bioRxiv2019

Second messengers and divergent HD-GYP enzymes regulate 3’,3’-cGAMP signaling

3,3-cyclic GMP-AMP (cGAMP) is the third cyclic dinucleotide (CDN) to be discovered in bacteria. No activators of cGAMP signaling have yet been identified, and the signaling pathways for cGAMP have appeared narrowly distributed based upon the characterized synthases, DncV and Hypr GGDEFs. Here we report that the ubiquitous second messenger cyclic AMP (cAMP) is an activator of the Hypr GGDEF enzyme GacB from Myxococcus xanthus. Furthermore, we show that GacB is inhibited directly by cyclic di-GMP, which provides evidence for cross-regulation between different CDN pathways. Finally, we reveal that the HD-GYP enzyme PmxA is a cGAMP-specific phosphodiesterase (GAP) that promotes resistance to osmotic stress in M. xanthus. A signature amino acid change in PmxA was found to reprogram substrate specificity and was applied to predict the presence of non-canonical HD-GYP phosphodiesterases in many bacterial species, including phyla previously not known to utilize cGAMP signaling.

biochemistry↗

bioRxiv2019

Bacterial interspecies interactions modulate pH-mediated antibiotic tolerance in a model gut microbiota

Despite decades of investigation into how antibiotics affect isolated bacteria, it remains highly challenging to predict consequences for communities in complex environments such as the human intestine. Interspecies interactions can impact antibiotic activity through alterations to the extracellular environment that change bacterial physiology. By measuring key metabolites and environmental pH, we determined that metabolic cross-feeding among members of the fruit fly gut microbiota drives changes in antibiotic sensitivity in vitro. Co-culturing of Lactobacillus plantarum with Acetobacter species induced tolerance to rifampin. Mechanistically, we found that acetobacters counter the acidification driven by L. plantarum production of lactate, and that pH shifts during stationary phase were sufficient to drive rifampin tolerance in L. plantarum monocultures. The key Lactobacillus physiological parameter related to tolerance was a reduction in lag time exiting stationary phase, opposite to a previously identified mode of tolerance to ampicillin in E. coli. Lactobacillus tolerance to erythromycin also depended on growth status and pH, suggesting that our findings generalize to other antibiotics. Finally, tolerance of L. plantarum to rifampin varied spatially across the fruit fly gut. This mechanistic understanding of the coupling among interspecies interactions, environmental pH, and antibiotic tolerance enables future predictions of growth and the effects of antibiotics in more complex communities and within hosts.

microbiology↗

bioRxiv2018

cGAMP signaling controls a transient surface-associated lifestyle

A newfound signaling pathway employs a GGDEF enzyme with unique activity compared to the majority of homologs associated with bacterial cyclic di-GMP signaling. This system provides a rare opportunity to study how signaling proteins natively gain distinct function. Using genetic knockouts, riboswitch reporters, and RNA-Seq, we show that GacA, the Hypr GGDEF in Geobacter sulfurreducens, specifically regulates cyclic GMP-AMP (3,3-cGAMP) levels in vivo to stimulate gene expression associated with metal reduction separate from electricity production. To reconcile these in vivo findings with prior in vitro results that showed GacA was promiscuous, we developed a full kinetic model combining experimental data and mathematical modeling to reveal mechanisms that contribute to in vivo specificity. A 1.4 [A]-resolution crystal structure of the Geobacter Hypr GGDEF domain was determined to understand the molecular basis for those mechanisms, including key cross-dimer interactions. Together these results demonstrate that specific signaling can result from a promiscuous enzyme.

biochemistry↗