Picture of Roseobacter: 
Description and Significance
Roseobacter is one of the most abundant and versatile microorganisms in the ocean. They are diversified across different types of marine habitats: from coastal to open oceans and from sea ice to seafloor. They make up around 25% of marine communities. During algal blooms, 20-30% of the prokaryotic community is Roseobacter.
Members of Roseobacter clade display diverse physiologies and are commonly found to be either free living, particle-associated, or in commensal relationships with marine phytoplankton, invertebrates, and vertebrates. Roseobacter is similar to phytoplankton in ways of living. Both of them colonize surface, scavenge iron and produce bioactive secondary metabolites.
Most of the Roseobacters analyzed so far have large genomes: ranging from 3.5Mbp to 5.0Mbp. The smallest found is the genome of Loktanella vestfoldensis SKA53 with 3.06 Mbp. The largest that of Roseovarius sp. HTCC2601 with 5.4 Mbp. In Jannaschia sp. CCS1, Silicibacter pomeroyi DSS-3, and Silicibacter sp. TM1040, the fraction of non-orthologous genes form 1/3 of the genomes. Plasmids are common to be seen in Roseobacters. The size of the plasmids ranges from 4.3 to 821.7 Kb. They can make up 20% of the genome content. Ecologically relevant genes can be found encoded on plasmids.
Genome plasticity could be a reason to explain the diversity and adaptability of Roseobacters, which is supported by the high number of probably conjugative plasmids. Linear conformation can be exhibited by plasmids, which is common for Roseobacters. In some strains, plasmid-borne takes place in a large proportion in genome content. Even though the mobility of plasmid has not yet been examined in the strains, they might contribute to the physiological diversity of Roseobacter.
Comparison and analysis of genomes of Roseobacter clade organisms are important because it can give insight in horizontal gene transfer and specific adaptation processes. As the Roseobacter population is widely distributed worldwide with distinct types of habitats, the success of Roseobacter clade can not be explained by only investigating one single population. Hence, the key to understanding why this clade is so abundant is to study the genetic as well as the metabolic diversity of organisms of the whole clade.
Cell Structure, Metabolism and Life Cycle
The Gram-negative Roseobacter species have been identified as both oval and rod-like shaped cells with either one or two flagella present, making them fully mobile. Their size can range from 4.3 kilobases to 821.7 kilobases. They have a mesophilic temperature range, are heterotrophs and anaerobic (as they are a marine species).
Roseobacter can have major implications for the turnover of organic material in the ocean as they consume decomposing organisms, also known as marine snow (phytoplankton or organic "aggregates". They freely swim throughout the water until they find a particle to colonize. It has been suggested that Roseobacter bacteria benefit from association with dimethylsulfoniopropionate (DMSP)-producing dinoflagellates because of the high metabolic rate at which Roseobacter can degrade them. The result of such associating is the use of both lyase and demethylation pathways.
Ecology and Known Roles in Symbiosis
The roseobacter clade is mostly found in the marine environment. The various species of roseobacter each have their own ecological niche. Several isolates have been captured from a vast number of ecosystems in coastal areas and open oceans. Roseobacters are a significant part of bacterial communities connected to phytoplankton, macroalgae, and several marine animals. Different lifestyles such as mutualistic and pathogenic have been proposed. Members of the clade are spread all over temperate and polar oceans and are also considerable in sea ice ecosystems. They are suggested to be extensive within coastal sediments, deep pelagic ocean, and deep-sea sediments. The roseobacter clade has an immense diversity of metabolic proficiency and regulatory circuits, which can be credited to their prosperity in a vast number of marine ecosystems.
Roseobacter strains have been found in a variety of places including the Mediterranean and New England. One of the most striking features of Roseobacter is the exceptional amount of variation between the strains in the different locations in which Roseobacter has been identified. One potential cause for concern is the number of unconfirmed strains that have been identified as of the Roseobacter species, which could lead to incorrect information if wrongly identified.
Marine bacteria that makes up to 25% of all bacteria in coastal and surface waters. Incredibly important for biogeochemical cycling of carbon and sulfur. Oxidizes carbon monoxide (Greenhouse gas), produced naturally in the ocean. Produce dimethylsulfide through degradation of algal osmolytes and dimethylsulfide catalyzes the formation of cloud condensation nuclei. Massive impact on global weather.
A strain of Roseobacter(deemed R. crassotreae) has been identified as an oyster pathogen leading to a disease called Juvenile Oyster Disease (JOD), severely affecting oysters in New England. What is most concerning about this recent increased mortality rate is the discovery of Roseobacter strains in apparently healthy oysters up a week prior to the outbreaks. Roseobacter has been affecting oysters for older than two years.
 Boettcher, K. J., Geaghan, K. K., Maloy, A. P., & Barber, B. J. (2005). Roseovarius crassostreae sp. nov., a member of the Roseobacter clade and the apparent cause of juvenile oyster disease (JOD) in cultured Eastern oysters. International Journal of Systematic and Evolutionary Microbiology, 55(4), 1531-1537.
 Miller, T. R., & Belas, R. (2004). Dimethylsulfoniopropionate metabolism by Pfiesteria-associated Roseobacter spp. Appl. Environ. Microbiol., 70(6), 3383-3391.
 Pinhassi, J., Simó, R., González, J. M., Vila, M., Alonso-Sáez, L., Kiene, R. P., ... & Pedrós-Alió, C. (2005). Dimethylsulfoniopropionate turnover is linked to the composition and dynamics of the bacterioplankton assemblage during a microcosm phytoplankton bloom. Appl. Environ. Microbiol., 71(12), 7650-7660.
 Geng, H., & Belas, R. (2010). Molecular mechanisms underlying Roseobacter–phytoplankton symbioses. Current opinion in biotechnology, 21(3), 332-338.
 Wagner-Döbler, I., & Biebl, H. (2006). Environmental biology of the marine Roseobacter lineage. Annu. Rev. Microbiol., 60, 255-280.
 Raina, J. B., Tapiolas, D., Willis, B. L., & Bourne, D. G. (2009). Coral-associated bacteria and their role in the biogeochemical cycling of sulfur. Appl. Environ. Microbiol., 75(11), 3492-3501.
This page was authored by Payton Rittenhouse as part of the 2020 UM Study USA led by Dr. Erik Hom at the University of Mississippi.