User:Jinoong31/Bacterioplankton

Article Draft
Below is my (in-progress) draft of new additions to the Wikipedia page Bacterioplankton.

Heterotrophic bacterioplankton
Roseobacter is a diverse and widely-distributed clade which makes up a significant contribution of marine bacterioplankton, accounting up to roughly 20% of coastal waters and 15% mixed layer surface oceans. Although many are heterotrophic, some are capable of performing a unique form of photosynthesis called aerobic anoxygenic phototrophy, which requires rather than produces oxygen.

Nitrogen
An analysis on metagenomes of 83 species of cyanobacteria has suggested the possible dissimilatory nitrate reduction to ammonium (DNRA) activity in certain cyanobacteria. Namely, the study found the presence of the NirBD gene, which is a marker for DNRA function, in the families Leptolyngbyaceae and Nostocaceae. Moreover, the study indicated that the cyanobacteria that had NirBD are largely also non-heterocyst nitrogen fixers, suggesting possible alternative strategies of acquiring nitrogen under varying environmental conditions. Nonetheless, the NirBD gene is also known to play a role in nitrogen assimilation and further studies are required to ascertain the function of NirBD in cyanobacteria.

Sulfur
Bacterioplankton, such as members of Roseobacter, SAR11, and Gammaproteobacteria, are known to contribute significantly towards the sulfur cycle, primarily through the metabolism of dimethylsulfoniopropionate (DMSP). DMSP can be catabolized either via means of cleavage to dimethylsulfide (DMS) or demethylation by bacterioplankton, in which both have contrasting effects on the sulfur cycle. The formation of DMS contributes to the sulfur flux into the atmosphere and according to the CLAW hypothesis, plays a role in regulating global climate. Increased production of sulfate aerosols from DMS oxidation are capable of promoting cooling on a global scale, via the promotion of cloud formation. In contrast, the demethylation pathway from DMSP to methanethiol results in the integration of carbon and sulfur into the organism itself as opposed to releasing the elements back to the environment. Bacterioplankton DMSP degradation is thought to be prevalent in marine surface waters, although the spatial distribution of the two aforementioned routes of degradation exhibit high variation.

Similar to DNRA, the same study indicated the presence of a dsyB-like gene in certain cyanobacteria genomes, suggesting DMSP producing ability. However, there has yet to be empirical confirmation of DMSP synthesis in cyanobacteria.

Silica
Diatoms are a major group of phytoplankton in which most have a requirement for silicon as biogenic silica to form their cell wall (known as frustule). Upon predation or death, particulate silica is released from diatoms but they need to be dissolved for recycling and reuptake by diatoms, otherwise silica will be exported out and deposited into sediment. Hence, the productivity of diatoms will be limited by silicon if dissolution rates are slow. However, it is known that bacterioplankton (i.e. members of Cytophaga-Flavobacterium-Bacteroides, Alphaproteobacteria, and Gammaproteobacteria) significantly promote the dissolution of particulate silica, thus maintaining the significant biogenic silica production in the ocean photic zone. It is also suggested that this process helps regulate diatom productivity and its corresponding biogeochemical effects.