Literature Review Blog 1

Environmental Microbiology: Microbial players involved in the decline of filamentous and colonial cyanobacterial blooms with a focus on fungal parasitism

Literature Review Blog

Over the last century, an increase in nutrients such as nitrogen (N) and phosphorus (P) has been discharged into freshwater ecosystems by anthropogenic means. The continuous surge of nutrients results in eutrophication; “an abundant accumulation of nutrients that supports the dense growth of algae and other organisms, the decay of which depletes the shallow waters of oxygen in summer” (Dictionary.com, 2009).  This intensification of nutrients is linked to cyanobacteria algae blooms that monopolize other phytoplankton aggregations. Therefore, expanding research and concisely understanding the role biotic factors play in conjunction with environmental factors can aid in advancement in complex microbial interactions from eutrophication. 

Phosphorus is a naturally forming element that is limited in most undistributed, natural setting environments. This natural limit, often restricts the growth of primary producers such as algae, other aquatic plants, cyanobacteria and photosynthetic bacteria (Adkins et al). But, due to human activities phosphorus is more readily available, consequently causing an exponentially unstable situation for fresh water ecosystems. The booming escalation of nutrients in addition to the effects of global warming have lead scientist to anticipate an expansion in dominance of adverse cyanobacteria. As a result, the adverse economic impact of cyanobacterial blooms is expected to worsen, “affecting recreational and angling activities, lake property values, and increasing the cost of drinking water treatment. It has been estimated that the annual cost of eutrophication was approximately $2.2 billion (USD) in US freshwater ecosystems” (Dodds et al., 2008). If eutrophication becomes a staple in fresh water environments, and the cyanobacteria dominance is held, there could potentially be a loss of phytoplankton heterogeneity corresponding to limiting the diversity of fish species in the affected systems.

The inner dynamics of the synergy between microbial and nutrient activities are enigmatic and challenging. There are several studies out in the scientific community, but all are encountering the same intricacies. There are four main natural biotic factors that promote the decline of cyanobacteria blooms; grazing, lysis by heterotrophic bacteria, viral lysis and fungal parasitism. To gather more definable data on the methods behind these interactions, each biotic factor was cross examined in a laboratory setting and natural setting.  The results of these experiments showed that the difference in settings accurately define the relationship between the available microbial communities, nutrients and decline of cyanobacteria blooms. The laboratory results were always different from the natural setting results. For each biotic factor, the reactions produced and decomposed different phytoplankton species.

Grazing deals with the morphology and toxicity of cyanobacteria, but the most important factor influencing zooplankton grazing is prey morphology.  The morphological and behavioral adaptations allow grazers to bypass this size constraint obliging for the size of filaments and colonies to shift for efficiency. Grazing also may limit the nitrogen readily available therefore, minimizing cyanobacterial growth.

 “After more than 20 years of research, interactions between cyanobacteria and zooplankton are still not resolved. Overall, there is no general rule regarding the capacity of grazers to control cyanobacterial blooms. It is clear, however, that herbivores can alter the structure of cyanobacterial populations. This top-down control and the inter-relationship with cyanobacterial morphology and toxicity are dependent on the specific species pairing (Wilson et al., 2006; Lemaire et al., 2012)”.

Lysis by heterotrophic bacteria uses cyanobacteria as a food source. “Bacterial lysis appears to function in three main ways: penetration into the host cell (Caiola and Pellegrini, 1984), cell to cell contact (Shunyu et al., 2006; Gumbo and Cloete, 2013) or most often production of extracellular compounds (Choi et al., 2005; Mu et al., 2007) such as peptides, proteins, amino acids or antibiotics which may or may not be host specific (Gumbo et al., 2008)”. Studies involving lysis by heterotrophic bacteria are mainly done in laboratory conditions. The microbial relationship in natural settings is too dynamic and yields inconsistent results.  It was proven that lysis can control cyanobacteria but is dependent on the setting.

Viral lysis is  always abundant in freshwater ecosystems due to viruses having an average concentration of 10⁷ and 10⁸ virus particles per mL in freshwater and marine ecosystems (Suttle, 2005; Wilhelm and Matteson, 2008; Gachon et al, 2015).  With the help of cyanophages, viruses-attacking cyanobacteria, the reduction of cyanobacteria is effortless and well maintained in any ecosystem. This natural technique is very affective but is host specific.

Fungal parasitism is still understudied in term of eutrophication. It is widely believe that this form of cyanobacteria control can become formidable with additional resources. Fungus is found in all freshwater sources and can replicate rapidly. Many hypothesize for this control method are still untested, making this practice more of a theoretical insight.  

All of these studies are highly acclaimed in scientific communities and have been performed multiple times, with diverse scenarios, by different scientist. But eventually, there is a breaking point where the research is not able to grasp what or why something is occurring. In natural environments there are too many factors that can contribute to any and all reactions in the system.  In laboratory conditions, it is a controlled environment in every aspect; temperature, air intake, microbial diversity, pH etc.).  The biotic factors are just too numerous and dynamic for scientist to completely perceive.

Studying the effects caused by eutrophication in a microbial aspect are paramount for future generations. There is a plethora of nutrients surging through our waterways. There are no real constrictions when it comes to anthropogenic uses; agriculture and livestock. This article brings to light the past discoveries and advancements for cyanobacteria bloom controls but also shows the many limitations. Scientist as a whole, still do not clearly understand the dynamics of the interactions between the food web involved and microbial behaviors with different conditions. The dynamics of these interactions are implausible for our understanding at the moment. If we can continue to build on the basics and dive deeper in to the subject some real breakthroughs can occur.     

               

Work Cited

Adkins, A., Leduc, D., et al. “ MICROORGANISMS: Role of Microorganisms in Phosphorous Cycling.” Department of Biology, University of Winnipeg.

Caiola, M.G., and Pellegrini, S. (1984). “Lysis of Microcystis aeruginosa (kütz.) by bdellovibrio-like bacteria.” J Phycol 20: 471–475

Choi, H., Kim, B., Kim, J., and Han, M. (2005). “Streptomyces neyagawaensis as a control for the hazardous biomass of Microcystis aeruginosa (Cyanobacteria) in eutrophic freshwaters.” Biol Control 33: 335–343

Dodds, W.K., Bouska, W.W., Eitzmann, J.L., Pilger, T.J., Pitts, K.L., Riley, A.J., et al. (2008) “Eutrophication of U.S. freshwaters: analysis of potential economic damages.” Environ Sci Technol 43: 12–19

Gachon, C., Gerphagonon, M., Gleason, F., Latour, D., Macarthur, D., Ogtrop, F., Sime-Ngando, T., et al. (2015). “ Microbial players involved in the decline of filamentous and colonial cyanobacterial blooms with a focus on fungal parasitism.” Environmental Mircobiology 17(8), 2573-2587.

Gumbo, R.J., Ross, G., and Cloete, E.T. (2008). “Biological control of Microcystis dominated harmful algal blooms.” Afr J Biotechnol 7: 4765–4773

Gumbo, J.R., and Cloete, T.E. (2013). “Light and electron microscope assessment of the lytic activity of Bacillus on Microcystis aeruginosa.” Afr J Biotechnol 10: 8054– 8063.

Lemaire, V., Brusciotti, S., van Gremberghe, I., Vyverman, W., Vanoverbeke, J., and De Meester, L., et al. (2012). “Genotype × genotype interactions between the toxic cyanobacterium Microcystis and its grazer, the waterflea Daphnia.” Evol Appl 5: 168–182.

Shunyu, S., Yongding, L., Yinwu, S., Genbao, L., and Dunhai, L. (2006). “Lysis of Aphanizomenon flos-aquae (Cyanobacterium) by a bacterium Bacillus cereus.” Biol Control 39: 345–351

Suttle, C.A. (2005). “Viruses in the sea.” Nature 437: 356–361

Thesaurus.com "atypical," in Roget's 21st Century Thesaurus, Third Edition. Source location: Philip Lief Group 2009.http://www.thesaurus.com/browse/atypical.

Wilhelm, S.W., and Matteson, A.R. (2008). “Freshwater and marine virioplankton: a brief overview of commonalities and differences.” Freshwater Biol 53: 1076–1089

Wilson, A.E., Sarnelle, O., and Tillmanns, A.R., et al. (2006). “Effects of cyanobacterial toxicity and morphology on the population growth of freshwater zooplankton: meta-analyses of laboratory experiments.” Limnol Oceanogr 51: 1915–1924

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