Bacterioplankton
The name comes from the Ancient Greek word πλαγκτός (planktós), meaning "wandering" or "drifting", and bacterium, a Latin term coined in the 19th century by Christian Gottfried Ehrenberg.
Photosynthetic bacterioplankton are responsible for a large proportion of the total primary production of aquatic food webs, supplying organic compounds to higher trophic levels.
Cyanobacteria, along with photosynthetic eukaryotes, are responsible for approximately half of the total global primary production[2] making them key players in the food web.
Green bacteria have different light harvesting pigments consisting of bacteriochlorophyll c, d and e.[1] These organisms do not produce oxygen through photosynthesis or use water as a reducing agent.
[12][13] 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.
[21][22] Anammox, a process in which ammonia is combined with nitrite in order to produce diatomic nitrogen and water, could account for 30–50% of production of N2 in the ocean.
[26] As mentioned above the microbial pump is responsible for the production of refractory DOM which is unavailable for biodegradation and remains dissolved in the oceans for thousands of years.
[16] The turnover of labile DOM organic material is quite high due to scarcity, this is important for the support of multiple trophic levels in the microbial community.
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.
[31][32] 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.
[34] Similar to DNRA, the same study indicated the presence of a dsyB-like gene in certain cyanobacteria genomes, suggesting DMSP producing ability.
[38] Cultured flagellates in laboratory experiments demonstrate that they are adapted to predation on bacteria-sized particles and occur in concentrations to control bacterial biomass.
With using prokaryotic inhibitors seasonally, there is a positive relationship between bacterial abundance and heterotrophic nanoplankton grazing rates and only 40-45 % of bacterioplankton production was observed to be consumed by phagotrophic Protozoa.
[42] Additionally, eukaryotic inhibitory experiments show that protozoan grazing has a positive effect on bacterioplankton production suggesting that nitrogen regeneration by Protozoa could be highly important for bacterial growth.
Eukaryotic inhibitors did not prove to be useful to determine protozoan grazing rates on bacterioplankton, however they may help understand control mechanisms in the microbial food web.
[42] Bacterioplankton such as cyanobacteria are able to have toxic blooms in eutrophic lakes which can lead to the death of many organisms such as fish, birds, cattle, pets and humans.
[48][50][49] Climate studies are also indicating that with increasing heat waves the likelihood of detrimental cyanobacterial blooms will become more of a threat to eutrophic freshwater systems.
[51][52][53] Other implications of the increasing average air temperature due to climate change is that there might be an expansion of the cyanobacterial bloom season, extending from earlier in the spring to later in the fall.
[54] Estimates of bacterioplankton abundance and density can be derived with a variety of methods including direct counts, flow cytometry, and conclusions drawn from metabolic measures.
These recycled nutrients can be reused by primary producers, thus increasing the efficiency of the biological food web and minimizing energy waste.
