Bacterial algicides: application strategies and cellular response of target organisms
| Author(s) | Wang, Yanfei | |
| Date Accessioned | 2022-02-02T16:27:02Z | |
| Date Available | 2022-02-02T16:27:02Z | |
| Publication Date | 2021 | |
| SWORD Update | 2021-09-30T19:12:23Z | |
| Abstract | Phytoplankton are primary producers and play an essential role in the aquatic food chains, while some species can form harmful algal blooms (HABs) that cause negative impacts on other organisms. Dinoflagellates are among the most toxigenic HAB species; their toxins can be transferred and accumulated through the aquatic food chains and cause illness of fish, shellfish, marine mammals, and even human beings. Conventional methods developed to control and mitigate HAB species include nutrient manipulation, clay flocculation, sonication, and application of toxic chemicals such as copper sulfate and hydrogen peroxide. While these methods are effective, they are either costly or pose a threat to other organisms in the environment, leading to the development of biological methods, including applying algicidal bacteria and their derivatives. ☐ Shewanella IRI-160 is a bacterium isolated from the Delaware Inland Bays and demonstrated algicidal effects that specifically target dinoflagellates while having no negative impacts on other algal species tested. Research indicated Shewanella IRI-160 can secrete a water-soluble compound(s), designated as IRI-160AA, that can control the growth of dinoflagellates without the requirement of direct algae-bacteria attachment. Investigations on marine organisms on higher trophic levels, including copepods, fish, and shellfish, demonstrated no negative impacts by IRI-160AA at concentrations required to control dinoflagellates. These results suggested the potential to use Shewanella IRI-160 and/or its algicide as an environmentally neutral means to control the growth of harmful dinoflagellates. ☐ Studies on dinoflagellate physiology and biochemistry revealed IRI-160AA destructured nuclei and chromosomes in dinoflagellates, accompanied by induced reactive oxygen species (ROS) production, DNA damage, cell cycle arrest, and caspase-3 like protease activity, suggesting a programmed pathway leading to cell death (PCD). Research on dinoflagellate photobiology also demonstrated impaired photosynthesis and disrupted photosynthetic electron transport. The cellular mechanisms underlying the algicidal effects of IRI-160AA at the molecular or metabolic levels remain unclear. Recent studies indicated ammonium is among the active algicidal compounds of IRI-160AA, while its effects were different from the algicide regarding dinoflagellate photobiology. Putrescine is also among the active substances in the algicide, implying the potential importance of the crosstalk between ammonium and putrescine on dinoflagellates. An inter-relationship between ammonium and putrescine has been demonstrated in animals and plants, while no research has focused on this relationship in algal species or the underlying molecular mechanism. ☐ In Chapter 2, methods for immobilization were developed for Shewanella IRI-160AA to explore the means for the bacterial application while avoiding biosafety concerns associated with mass bacterial dispersal. Shewanella IRI-160 was immobilized to different porous matrices, including agarose, alginate hydrogel, cellulosic sponge, and polyester foam. The bacterial retention was evaluated at 4 and 25 °C for 12 days. Results suggested solid matrices may protect Shewanella IRI-160 under adverse conditions. Superior retention of Shewanella IRI-160 by alginate hydrogel was also demonstrated, with over 99% cells still embedded in the alginate hydrogel beads rather than released into the surrounding medium after 12 days. An investigation on the effects of immobilized Shewanella IRI-160 in alginate beads on dinoflagellates Karlodinium veneficum and Prorocentrum minimum, as well as a control cryptophyte species Rhodomonas was followed. The results illustrated the efficacy of these immobilized bacteria to control the growth of dinoflagellates as soon as 24 hours after the treatment while having no adverse impacts on Rhodomonas. Overall, this research suggested immobilized Shewanella IRI-160 may serve as an environmentally neutral means to control HABs. Immobilizing Shewanella IRI-160 in biodegradable matrices, such as alginate hydrogel, may protect bacteria from adverse environments for long-lasting performance and provide extra advantages to avoid the release of harmful contaminants such as microplastic into the environment. This research also provided future directions for studies addressing the prevention and mitigation of HAB species. ☐ In Chapter 3, a transcriptomic analysis was conducted on K. veneficum exposed to IRI-160AA to understand the underlying molecular mechanisms of the algicidal effects. To differentiate the molecular effect of IRI-160AA and ammonium, transcriptomic analysis was also conducted on K. veneficum treated with ammonium. K. veneficum treated with the algicide was also subjected to a metabolomic analysis to explore the accompanied metabolic changes. Furthermore, to explain the specificity of IRI-160AA to dinoflagellates, a metabolomic analysis was also conducted on the control cryptophyte Rhodomonas. Results of the transcriptomic analysis demonstrated differential impacts of ammonium and IRI-160AA, as the highly differentially expressed genes (DEGs; FDR<0.001, fold-change>4) regulated by ammonium and the algicide only shared 17% enriched biological processes, while over 80% processes were only enriched by the DEGs that were regulated by ammonium or the algicide alone. The transcriptome analysis revealed a global response in K. veneficum to the algicide exposure, supported by enriched processes impacting diverse cellular levels, including gene expression, protein activity, and cellular morphology. Consistent with previous reported physiological data, DEGs involved in ROS, DNA damage response, and PCD were identified in the algicide treated K. veneficum. Altered metabolites involved in these processes were also identified in the cell pellets of K. veneficum but not Rhodomonas responding to the algicide. The transcriptomics and metabolomics of K. veneficum exposed to the algicide also suggested the involvement of a photorepair mechanism. Overall, results of this research further differentiated the effects of ammonium and IRI-160AA on K. veneficum and illustrated the mechanisms underlying the algicidal activity of IRI-160AA against dinoflagellates at the transcriptomic and metabolomic levels. ☐ In Chapter 4, the effects of putrescine and ammonium were evaluated on the dinoflagellates K. veneficum, P. minimum, and Levanderina fissa. Dose-dependent synergistic effects by these compounds were observed with K. veneficum and L. fissa but not on P. minimum at the concentrations tested. To explore the molecular mechanism behind the synergistic effects, transcriptomic analysis was conducted on K. veneficum exposed to ammonium, putrescine, or a combination of ammonium and putrescine. A number of DEGs involved in polyamine biosynthesis and catabolism, as well as ammonium transport and assimilation, were only regulated in the treatment with a combination of putrescine and ammonium, suggesting polyamine homeostasis disruption and reduced ammonium toxicity tolerance triggered by the synergistic effects. Results also implied impaired photosynthesis and an inability for photorepair in K. veneficum under the synergistic effects. Furthermore, crosstalk between the synergistic effect induced cell death and other essential biological processes was suggested. These processes included mitochondrial fission, ion and cation transport, mechanical stimulus response, meiotic cell cycle, flagellar assembly and movement, as well as diverse signal transduction pathways. Overall, this research expanded our knowledge in polyamine biology and illustrated the underlying molecular mechanism of the crosstalk of ammonium and putrescine in algal species. | en_US |
| Advisor | Coyne, Kathryn J. | |
| Degree | Ph.D. | |
| Department | University of Delaware, School of Marine Science and Policy | |
| DOI | https://doi.org/10.58088/tkj0-3c75 | |
| Unique Identifier | 1294513243 | |
| URL | https://udspace.udel.edu/handle/19716/30239 | |
| Language | en | |
| Publisher | University of Delaware | en_US |
| URI | https://login.udel.idm.oclc.org/login?url=https://www.proquest.com/dissertations-theses/bacterial-algicides-application-strategies/docview/2591168878/se-2 | |
| Keywords | Algicide | |
| Keywords | Dinoflagellates | |
| Keywords | Harmful algal blooms | |
| Keywords | Immobilized bacteria | |
| Keywords | Polyamine | |
| Keywords | Shewanella | |
| Title | Bacterial algicides: application strategies and cellular response of target organisms | en_US |
| Type | Thesis | en_US |