Saprotrophic bacteria

Saprotrophic bacteria are bacteria that are typically soil-dwelling and utilize saprotrophic nutrition as their primary energy source. They act as important decomposers, connecting the foundation of the food web, but they can also tie up nutrients in an ecosystem, leaving them as an ecologically limiting factor.[1] Saprotrophic bacteria are often associated with soil fungi that also use saprotrophic nutrition and both are classified as saprotrophs.[2]

Some saprotrophic bacteria may be vectors for food borne illnesses such as Escherichia coli.[2] They are common pathogens in medicine and agriculture, as they move readily between individuals via consumption or other modes of exposure, such as contact with excrement.[3] When cultivating a new environment, the population of a saprotrophic strain of bacteria initially decreases and then reaches a point of population stabilization.[3][4] While they are common in soil environments, they can persist anywhere with available food resources, such as in aquatic environments, or in fecal matter.[3]

Community composition and proliferation rates of saprotrophic indicator bacteria are often considered signals of community health in soil, aquatic,[5] and bodily systems.[6] Growth rates of saprotrophic bacteria are impacted by local temperatures, moisture fluctuations, pH, plant and fungi presence, toxin levels, and their growth substrate.[7] These factors can, in turn, alter the rates of decomposition and soil organic matter turnover, impacting ecosystem productivity.[8]

Nutrient cycling and MEEs

Through saprotrophic nutrition, saprotrophic bacteria release microbial extracellular enzymes (MEEs) into the environment to break down soil organic matter (SOM). MEEs are released when an organism's energy and nutrient needs are not being met. This allows for the monitoring of MEEs as an indicator of nutrient availability in soil.[9] Some significant MEEs are:

  • Phenol oxidases (PHO): PHOs can biodegrade or detoxify aromatic pollutants into sources of carbon. Additionally, PHO's act as an indirect hydrolases in peat bogs, which accelerate the decomposition of soil organic matter. PHO's break down phenolics, which inhibit hydrolases. Thus, when microorganisms are limited, decomposition is also limited. This process has been termed an "enzymatic latch."[10][9]
  • β-glucosidase (GLU): GLUs are involved in securing energy sources and labile carbon for microorganisms. This is accomplished through the catalysis of the release of monosaccharides and the hydrolysis of oligosaccharides.[9]
  • Acid (alkaline) phosphatase (AP): APs can be used as indicators for P mineralization potential and availability in soil.[9]

References
  1. Anderson, R.V.; Coleman, D.C.; Cole, C.V. (1981). "EFFECTS OF SAPROTROPHIC GRAZING ON NET MINERALIZATION". Ecological Bulletins (33): 201–216. ISSN 0346-6868.
  2. "saprotroph | Definition, Description, & Major Groups". Encyclopedia Britannica. Retrieved 2021-03-23.
  3. Kupriyanov, A. A.; Semenov, A. M.; Van Bruggen, A. H. C. (2010-06-01). "Transition of entheropathogenic and saprotrophic bacteria in the niche cycle: Animals-excrement-soil-plants-animals". Biology Bulletin. 37 (3): 263–267. doi:10.1134/S1062359010030076. ISSN 1608-3059.
  4. Kozhevin, P.A., Mikrobnye populyatsii v prirode (Microbial Populations in Nature), Moscow: Mosk. Gos. Univ., 1989.
  5. Donsel, Dale J. Van; Geldreich, Edwin E.; Clarke, Norman A. (1967-11-01). "Seasonal Variations in Survival of Indicator Bacteria in Soil and Their Contribution to Storm-water Pollution". Applied Microbiology. 15 (6): 1362–1370. ISSN 0003-6919. PMID 16349746.
  6. Shin, Na-Ri; Whon, Tae Woong; Bae, Jin-Woo (September 2015). "Proteobacteria: microbial signature of dysbiosis in gut microbiota". Trends in Biotechnology. 33 (9): 496–503. doi:10.1016/j.tibtech.2015.06.011. ISSN 0167-7799.
  7. Rousk, Johannes; Bååth, Erland (2011-10-01). "Growth of saprotrophic fungi and bacteria in soil". FEMS Microbiology Ecology. 78 (1): 17–30. doi:10.1111/j.1574-6941.2011.01106.x. ISSN 0168-6496.
  8. Ed.D, Eddie Funderburg. "What Does Organic Matter Do In Soil?". Noble Research Institute. Retrieved 2021-04-16.
  9. Luo, Ling; Meng, Han; Gu, Ji-Dong (2017-07-15). "Microbial extracellular enzymes in biogeochemical cycling of ecosystems". Journal of Environmental Management. 197: 539–549. doi:10.1016/j.jenvman.2017.04.023. ISSN 0301-4797.
  10. Freeman, Chris; Ostle, Nick; Kang, Hojeong (January 2001). "An enzymic 'latch' on a global carbon store". Nature. 409 (6817): 149–149. doi:10.1038/35051650. ISSN 1476-4687.
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