Polynucleobacter
Polynucleobacter
Polynucleobacter is a genus of Gram-negative bacteria found in almost all types of freshwater habitats worldwide. These microorganisms are often extremely abundant and can constitute up to 20% of the total bacterial community in lakes. The genus includes both free-living species and obligate endosymbionts living within ciliates of the genus Euplotes. They play a fundamental role in the microbial loop by efficiently utilizing dissolved organic carbon.
Details
Identification
Rod-shaped morphology, Gram-negative, often very small (ultramicrobacterial), identification usually via 16S rRNA sequencing.
Social behavior
Mostly solitary or as endosymbionts in ciliates.
Diet
Heterotrophic nutrition by uptake of dissolved organic matter (DOM), especially photo-oxidation products of humic substances.
Overwintering
Reduced metabolism during cold periods.
Ecology
Ecological role
Central player in the microbial loop; converts dissolved carbon into biomass available for higher trophic levels (flagellates).
Natural predators
Heterotrophic nanoflagellates (HNF) and bacteriophages.
Competitor species
Other pelagic freshwater bacteria such as Actinobacteria (e.g., acl lineage).
Ecosystem service
Self-purification of water bodies through degradation of organic loads and nutrient recycling.
Threats
Severe acidification or extreme chemical pollution of water bodies.
Scientific profile
Profile
Habitat
Pelagic zone of freshwater lakes, ponds, and rivers worldwide; particularly abundant in acidic, humic-rich (dystrophic) waters as well as in oligotrophic high-mountain lakes.
Ecological role
Key role in the microbial loop of freshwater systems; often constitutes 10-60% of total bacterial biomass. Important link in the food web as prey for nanoflagellates.