Pelagibacter ubique represents a specific type of marine bacterium, recognized as a member of the SAR11 clade. This group is considered one of the most widespread and successful collections of organisms on the planet. This tiny microbe inhabits the global oceans, playing a substantial role in marine environments.
Discovery and Abundance
The discovery of Pelagibacter ubique did not follow traditional laboratory culturing methods. Researchers initially identified its presence through genetic sequencing of ribosomal RNA genes from seawater samples collected in the Sargasso Sea in 1990. It was later successfully isolated and given its specific name in 2002.
This bacterium’s name, ubique, meaning “everywhere,” accurately reflects its sheer prevalence in marine environments. Pelagibacter ubique and its relatives are estimated to comprise approximately 25% of all microbial plankton cells in the oceans. During summer months, their numbers can increase, accounting for around half of the cells found in temperate ocean surface waters. To put this into perspective, a single teaspoon of seawater can contain millions of these microscopic organisms.
Unique Biological Characteristics
The biology of Pelagibacter ubique is distinguished by its remarkably streamlined genome, one of the smallest known for any free-living organism. Its genome contains approximately 1.3 million base pairs and encodes about 1,354 predicted protein-coding genes, focusing on essential functions. This genetic efficiency means it lacks non-coding segments like pseudogenes, introns, or transposons, and features the shortest intergenic spacers.
This genetic minimalism translates directly into its physical characteristics, as Pelagibacter ubique is an exceptionally small bacterium. Its cell dimensions typically range from 0.12 to 0.20 micrometers in diameter and 0.37 to 0.89 micrometers in length, with an average cell volume of 0.025 to 0.045 cubic micrometers. This small size, coupled with its streamlined genome, provides a competitive advantage in the oligotrophic conditions of the open ocean, an environment characterized by low nutrient concentrations. The organism’s design allows it to efficiently acquire and process the limited available nutrients, maximizing its surface-to-volume ratio for effective resource uptake.
Role in Global Ecosystems
Pelagibacter ubique plays a substantial role in Earth’s biogeochemical cycles, particularly in the marine carbon cycle. These bacteria are consumers of dissolved organic carbon (DOC), which includes the breakdown products from other marine organisms. By processing this organic matter, Pelagibacter ubique converts it back into carbon dioxide, contributing to the “bacterial loop” where organic matter is recycled within the microbial community rather than moving up the food web. This process helps regulate the ocean’s carbon balance and influences atmospheric carbon dioxide levels.
Beyond carbon, Pelagibacter ubique also participates in the global sulfur cycle. It metabolizes dimethylsulfoniopropionate (DMSP), a compound produced by marine phytoplankton, into dimethyl sulfide (DMS). DMS is a volatile gas that can escape from the ocean into the atmosphere. Once in the atmosphere, DMS plays a role in the formation of cloud condensation nuclei, which are particles around which water vapor condenses to form clouds. This connection suggests a potential influence on cloud formation and Earth’s climate regulation.