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
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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