Biology subjects

Haavisto, V.

Publications and source records attributed to Haavisto, V..

3 recordsLinked to original sources

bioRxiv2026

Crossfeeding interactions in a minimal marine chitin-degrading community

Communities of heterotrophic particle-associated marine bacteria contribute to oceanic carbon cycling through interspecies interactions that can influence polysaccharide degradation. While these interactions have been extensively studied using single natural isolates or pairwise combinations thereof, their mechanistic relevance within multispecies communities remains unclear. To address this gap, we developed MCC4, a minimal chitin-degrading bacterial community consisting of two chitin degraders and two non-degrading isolates that represent globally prevalent marine bacterial taxa. We show that the community remains stable across ten growth-dilution cycles, establishing a reproducible model for controlled multi-isolate experiments. Using transcriptomic and metabolomic analyses combined with metabolite supplementation assays, we uncovered the underlying crossfeeding network. While one degrader drives chitin degradation, the other exploits chitin monomers and chitooligomers generated by the main degrader. The two non-degraders are sustained by consuming deacetylated chitin monomers, 2-carbon compounds, nucleotides, and branched-chain amino acids, likely released by degraders. Community assembly is driven by competitive scavenging abilities, potentially complemented by specific survival strategies such as increased motility and deployment of type VI secretion systems. Despite its simplicity, MCC4 captures dynamic microbial interactions characteristic of natural marine ecosystems. It offers a tractable, reproducible framework for investigating how environmental perturbations impact community function and testing ecological theories in particle-associated marine environments.

microbiology↗

bioRxiv2026

Negative and neutral interactions are prevalent in interactions between marine chitin degraders

Bacterial chitin degradation contributes to global carbon cycling, particularly in marine environments where it is a highly abundant polysaccharide. Despite the taxonomic diversity of co-occurring chitin-degrading bacteria, the influence of individual traits on interactions between them remains poorly understood. Here, we measured key physiological traits of seven chitin degraders and investigated how these traits shape interaction outcomes and chitin degradation in pairwise cocultures. We found mainly negative and neutral interactions among degraders, contrasting with the synergistic dynamics observed with other complex polysaccharides. However, chitin degradation was not consistently diminished. These interaction types could be attributed to the limited partitioning of degradation products, alongside variations in enzyme repertoires and attachment behaviours that help some degraders to prevail over others. Further, we showed that one degrader can strongly inhibit the growth of others, even those possessing favourable physiological traits, likely due to the secretion of inhibitory compounds. These findings extend our understanding of the breadth of interactions among primary polysaccharide degraders and their implications for the degradation process. One-sentence SummaryThe physiological traits of bacteria that degrade chitin, a highly abundant biopolymer in marine environments, promote a range of neutral and negative interactions among them.

microbiology↗

bioRxiv2023

High-throughput profiling of metabolic responses to exogenous nutrients in Synechocystis sp. PCC 6803

Cyanobacteria fix carbon dioxide and release carbon-containing compounds into the wider ecosystem, yet they are sensitive to small metabolites that may impact their growth and physiology. Several cyanobacteria can grow mixotrophically, but we currently lack a molecular understanding of how specific nutrients may alter the compounds they release, limiting our knowledge of how environmental factors might impact primary producers and the ecosystems they support. In this study, we develop a high-throughput phytoplankton culturing platform and identify how the model cyanobacterium Synechocystis sp. PCC 6803 responds to nutrient supplementation. We assess growth responses to 32 nutrients at two concentrations, identifying 15 that are utilized mixotrophically. Seven nutrient sources significantly enhance growth, while 19 elicit negative growth responses at one or both concentrations. High-throughput exometabolomics indicates that oxidative stress limits PCC 6803s growth, but may be alleviated by antioxidant metabolites. Furthermore, glucose and valine induce strong changes in metabolite exudation in a possible effort to correct pathway imbalances or maintain intracellular elemental ratios. This study sheds light on the flexibility and limits of cyanobacterial physiology and metabolism, as well as how primary production and trophic food webs may be modulated by exogenous nutrients. ImportanceCyanobacteria capture and release carbon compounds to fuel microbial food webs, yet we lack a comprehensive understanding of how external nutrients modify their behavior and what they produce. We developed a high throughput culturing platform to evaluate how the model cyanobacterium Synechocystis sp. PCC 6803 responds to a broad panel of externally supplied nutrients. We found that growth may be enhanced by metabolites that protect against oxidative stress, and that growth and exudate profiles are altered by metabolites that interfere with central carbon metabolism and elemental ratios. This work contributes a holistic perspective of the versatile response of PCC 6803 to externally supplied nutrients, which may alter carbon flux into the wider ecosystem.

microbiology↗