Pollutants, including synthetic fertilizer and heavy metals, are known to
adversely affect the aquatic ecosystem and physiological systems in planktonic
species studied to date. While many studies reported the direct effects of the
chemicals on single organism, the toxicity on the metabolic interactions within the
holobiant are of particular concern because the toxic effects on one symbiotic
component can highly affect the survival of the holobiant as a whole. This thesis
studied the effects of anthropogenetic stress on the metabolic reactions of holobiant
and microbial communities in the ultraoligotrophic ecosystem.
Due to the extensive fertilizer usage and sewage effluent inputs, the
interconversion between nitrogen and phosphorus limitation triggered the nutrient
stoichiometry of phy...[
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Pollutants, including synthetic fertilizer and heavy metals, are known to
adversely affect the aquatic ecosystem and physiological systems in planktonic
species studied to date. While many studies reported the direct effects of the
chemicals on single organism, the toxicity on the metabolic interactions within the
holobiant are of particular concern because the toxic effects on one symbiotic
component can highly affect the survival of the holobiant as a whole. This thesis
studied the effects of anthropogenetic stress on the metabolic reactions of holobiant
and microbial communities in the ultraoligotrophic ecosystem.
Due to the extensive fertilizer usage and sewage effluent inputs, the
interconversion between nitrogen and phosphorus limitation triggered the nutrient
stoichiometry of phytoplankton. The effects of nutrient-imbalanced prey
(phytoplankton) on the interactions between gut microbiota and zooplankton were
studied. Our results revealed that under a nutrient-imbalanced diet, the microbes not
only benefit themselves by absorbing excess nutrients inside the zooplankton gut but
also help zooplankton to survive during the nutrient limitation. This mutually
beneficial symbiotic relationship illustrated the crucial role of symbiotic interactions
within the holobiant in adapting to anthropogenetic stress.
The effects of anthropogenic antibacterial silver (Ag) species (including silver
nanoparticles: AgNPs and silver ions: Ag
+) on the interactions between gut microbiota
and zooplankton were also studied. The results demonstrated that the gut-accumulated
Ag
+ and AgNPs were transformed by gut-microbial sulfidation, which subsequently
affected the toxic symptoms of D. magna. In addition, the toxic adapted gut microbes
can be maternally transferred to the next generation. The chromatic exposure under a
high concentration of AgNPs will cause the extinction of gut microbes, which further
results in the loss of detoxification capability and the death of the host. This result
revealed a more complex toxic adaptation mechanism of the holobiant to Ag
pollutants, and the strong toxic effects on one symbiotic component could highly
affect the whole holobiant.
Further study about the toxic differences between Ag
+ and AgNPs revealed that
the gut-enriched organic matter plays a distinct role in different Ag species' gut
microbial detoxification process. The gut-enriched organic matter functioned as an electron donor for sulfidation-based detoxification of Ag
+ through degradation and
inhibitor of Ag
+ released from AgNPs by surface adsorption. This finding
demonstrated that the toxic effects of Ag pollutants on holobiant can be highly related
to the chemical format, and the organic matter is essential for the detoxification
process of Ag pollutants.
To investigate the metabolic reactions of the microbial community exposed to
silver (Ag) species (including silver nanoparticles: AgNPs and silver ions: Ag
+), we
conducted a marine mesocosm-based metatranscriptomic study in the
ultraoligotrophic Mediterranean. We revealed the taxon-specific inhibition of Ag
pollutants on the phytoplankton groups' nutrient assimilation and photosynthetic
process, indicating the strong effects of Ag pollutants on the biosynthesis of organic
matter. The carbohydrate degradation supported microbial sulfidation of Ag pollutants
is revealed to be crucial for the bio-remediation of Ag pollutants in the
ultraoligotrophic Mediterranean. However, with little terrestrial input of organic
sources in the ultraoligotrophic environment, the inhibition of Ag pollutants on
photosynthesis may further constrain the microbial remediation of Ag pollutants in the
ultraoligotrophic environment. Therefore, the anthropogenic Ag species may pose
higher threads on the ultraoligotrophic ecosystem than the ecosystem with rich
nutrients.
In summary, this thesis extend our knowledge of the metabolic interactions
within aquatic holobiant and microbial community in responding to anthropogenic
stress.
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