User:Cbaughan/marinesnow

Particle Associated Bacteria
Planktonic prokaryotes are further defined into two categories, free-living or particle associated. The two are separated by filtration. Particle-associated bacteria are often difficult to study, because marine snow aggregates are often ranging in sizes from 0.2 to 200 μm, sampling efforts are often difficult. These aggregates are hotspots for microbial activity.

A major component of marine snow are the bacteria that colonize the aggregates. Bacteria are largely responsible for the remineralisation and fragmentation of aggregates.

Microbial communities that form on the aggregates vary from the communities in the water column. The concentration of attached microbes are typically orders of magnitude larger than free-living microbes. Isolated bacterial cultures have up to 20-times more enzymatic activity within 2 hours of aggregate attachment.

It was previously thought that due to fragmentation, bacterial communities would shift as they travel down the water column. As seen in experiments, it now appears that the communities that form during aggregation remain associated with the aggregate and any community changes are due to grazing or fragmentation rather than new bacterial colony formation.

Carbon Cycling
The deep ocean harbors more than 98% of the dissolved inorganic carbon(DIC) pool. Along with a rapid sedimentation rate that results in low particulate organic carbon(POC) inputs It is yet to be resolved what effect microbes have on the global carbon cycle. Studies show that microbes in the deep ocean are not dormant, but are metabolically active and must be participating in nutrient cycling by not only heterotrophs but by autotrophs as well. There is a mismatch from the microbial carbon demand in the deep ocean and the carbon export from the surface ocean. DIC fixation is on similar orders of magnitude as heterotrophic microbes in the surface ocean. Model based data reveal DIC fixation ranges from 1 mmol C m-2 d-1 to 2.5 mmol C m-2 d-2.

Mesopelagic single amplified genomes(SAGs) of Deltaproteobacteria and Gammaproteobacteria have been seen to encode key enzymes for the large subunit of ribulose-1,5-bisphosphate xcarboxylase-oxygenase (RuBisCO). This is the first record for the Deltaproteobacteria SAR 324. Chemoautotrophy cannot proceed without an energy source. Carbon fixation is thought to be fueled by nitrogen as an energy source. Genes encoding enzymes required for nitrification were recovered in SAGs of Crenarchaeota. No nitrification genes were recovered in bacterial lineages, but several sulfur oxidation genes were able to be recovered in SAGs which indicate these lineages may be Mixotroph s.

Microenvironments
Large aggregates can become anoxic which give rise to anaerobic metabolisms. Typically anaerobic metabolisms are confined to areas where it is more energetically favorable. Give the abundance of denitrifying and sulfate-reducing bacteria it is thought that these metabolisms are able to thrive within marine snow aggregates. In a model developed by Bianchi et al., it shows the various redox potentials within an aggregate.