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...[ Read more ]

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.