Microbial food web

The microbial food web refers to the combined trophic interactions among microbes in aquatic environments. These microbes include viruses, bacteria, algae, heterotrophic protists (such as ciliates and flagellates). In aquatic ecosystems, microbial food webs are essential because they form the basis for the cycling of nutrients and energy. These webs are vital to the stability and production of ecosystems in a variety of aquatic environments, including lakes, rivers, and oceans. By converting dissolved organic carbon (DOC) and other nutrients into biomass that larger organisms may eat, microbial food webs maintain higher trophic levels. Thus, these webs are crucial for energy flow and nutrient cycling in both freshwater and marine ecosystems.

Role of Different Microbes
In aquatic environments, microbes constitute the base of the food web. Single celled photosynthetic organisms such as diatoms and cyanobacteria are generally the most important primary producers in the open ocean. Many of these cells, especially cyanobacteria, are too small to be captured and consumed by small crustaceans and planktonic larvae. Instead, these cells are consumed by phagotrophic protists which are readily consumed by larger organisms.

Viruses

Aquatic ecosystems are full of viruses, which are essential for managing microbial populations. They release organic matter back into the environment by infecting and lysing planktonic algae (phycoviruses) and bacterial cells (bacteriophages). This mechanism, called the viral shunt, promotes nutrient recycling and aids in the control of microbial populations. Viral particles and dissolved organic carbon (DOC), which can be further used by other microorganisms, are released when bacterial cells are lysed. Viruses can infect and break open bacterial cells and (to a lesser extent), planktonic algae (a.k.a. phytoplankton). Therefore, viruses in the microbial food web act to reduce the population of bacteria and, by lysing bacterial cells, release particulate and dissolved organic carbon (DOC).

Bacteria

In the microbial food web, bacteria play a crucial role in breaking down organic materials and recycling nutrients. They transform DOC into bacterial biomass so that protists and other higher trophic levels can consume it. Additionally, bacteria take part in the nitrogen and carbon cycles, among other biogeochemical cycles.

Algae

In aquatic ecosystems, single-celled photosynthetic organisms like cyanobacteria and diatoms are the main producers. Through the process of photosynthesis, they transform sunlight into chemical energy and create organic matter, which is the foundation of the food chain. Particularly significant in nutrient-poor environments are cyanobacteria because of their capacity to fix atmospheric nitrogen. When vital nutrients like nitrogen and phosphorus are scarce during periods of uneven development, algal cells have the potential to produce DOC. DOC may also be released into the environment by algal cells. One of the reasons phytoplankton release DOC termed "unbalanced growth" is when essential nutrients (e.g. nitrogen and phosphorus) are limiting. Therefore, carbon produced during photosynthesis is not used for the synthesis of proteins (and subsequent cell growth), but is limited due to a lack of the nutrients necessary for macromolecules. Excess photosynthate, or DOC is then released, or exuded.

Heterotrophic Protists

In the microbial food web, protists including ciliates and flagellates are significant consumers. By consuming bacteria, algae, and other tiny particles, they move nutrients and energy up the food chain. Larger creatures like zooplankton feed on these protists in turn.

Microbial Interactions
The food web's microbial interactions are varied and diverse. Predation, rivalry, and symbiotic connections are some of these interactions. For instance, certain bacteria and algae create mutualistic relationships in which the bacteria give the algae vital nutrients, and the algae give the bacteria organic carbon. Microbial communities can be shaped by competition for resources like light and nutrition, which can affect their makeup and functionality.

Environmental Factors
Environmental factors that have a significant impact on microbial food webs include temperature, availability of light, and nutrient concentrations. Microbe development and metabolic rates are influenced by temperature, and photosynthetic organisms are impacted by light availability. The availability of nutrients, especially phosphorus and nitrogen, might restrict the growth and productivity of microorganisms. For instance, during times of nitrogen constraint, phytoplankton may emit DOC, a phenomenon referred to as imbalanced growth.

Human Impact
A major impact of human activity on microbial food webs is eutrophication, pollution, and climate change. The activities of microbial communities can be disturbed by pollutants like pesticides and heavy metals. Microbial growth and dispersal are impacted by temperature and precipitation changes brought about by climate change. The entire aquatic food chain may be impacted by eutrophication, which is brought on by nutrient runoff from cities and farms. Eutrophication can also result in toxic algal blooms and hypoxic conditions.

Technological Advances
Technological developments have completely changed the way that microbial food webs are studied. By analyzing genetic material from environmental samples, researchers can get insights into the diversity and roles of microbial communities using metagenomics. The utilization of remote sensing technology facilitates the large-scale monitoring of environmental variables and microbial activity, consequently augmenting our comprehension of microbial dynamics across various ecosystems.

The Microbial Loop
The microbial loop describes a pathway in the microbial food web where DOC is returned to higher trophic levels via the incorporation into bacterial biomass. This loop makes sure that the DOC created by photosynthetic organisms is used by heterotrophic bacteria and then moves up the food chain, which is crucial for sustaining the flow of nutrients and energy within the ecosystem.

Conclusion
By facilitating the transfer of nutrients and energy, microbial food webs are essential for the health and stability of aquatic ecosystems. It is crucial to comprehend these complex relationships to address environmental issues and advance sustainable management of aquatic resources. Technological developments keep expanding our understanding and illuminating the complex mechanisms that support life in the oceans of our planet.

Other references

 * Michaels, A.F. and Silver, M.W. (1988) "Primary production, sinking fluxes and the microbial food web". Deep Sea Research Part A. Oceanographic Research Papers, 35(4): 473–90.