The interaction of free-living amoeba with rice bacterial and fungal pathogens
| dc.contributor.author | Long, Jia Jun, author | |
| dc.contributor.author | Leach, Jan E., advisor | |
| dc.contributor.author | Jahn, Courtney E., advisor | |
| dc.contributor.author | Jackson, Mary, committee member | |
| dc.date.accessioned | 2018-06-12T16:14:29Z | |
| dc.date.available | 2018-06-12T16:14:29Z | |
| dc.date.issued | 2018 | |
| dc.description.abstract | Free-living amoebae are ubiquitous microbes found in the soil and water across the globe. Amoebae live a predominantly heterotrophic lifestyle – preying on a variety of organisms including bacteria, fungi and even other protists. Although extensively studied, their potential as a biocontrol for agricultural pathogens is largely unexplored. As many pathogens occupy the same habitat as amoeba, we investigated their interactions as a first step to determine if amoeba are possible biocontrol agents. Our research focuses on two important pathogens of rice, the bacteria Xanthomonas oryzae and the fungus Rhizoctonia solani. Much of this thesis centers on the interaction between amoebae and X. oryzae, which is explored in depth and presented in the first chapter. Experimentation involved five common amoebal species and two highly virulent X. oryzae pathovars. Microscopy and vitality assays of amoebae-bacteria co-cultures first established that X. oryzae does not grow or dies in the presence of our amoebae. On the other hand, amoebae are not adversely affected, with most cells remaining alive in the metabolically active trophozoite form. Although the bacteria are harmed in this interaction, it is likely not through phagocytosis, the most common and well-studied tactic that amoeba use to feed. Observations made through confocal microscopy revealed that X. oryzae was rarely detected inside amoebae. Furthermore, lysis of amoebae after exposure to bacteria did not yield any viable bacteria, suggesting that either bacteria are rarely internalized and/or that X. oryzae does not survive in the amoeba cell. Conversely, amoebal trophozoites have no impact on the biofilms of X. oryzae either. These data indicate that amoeba do not directly or physically interact with X. oryzae. Instead, our amoeba-conditioned media assays reveal that amoeba alter the media and render it harmful to X. oryzae. The most likely scenario is that amoeba secrete a bactericidal agent into their surroundings. At this time, we have yet to isolate or identify the compound, but its presence may prove to be a boon with a variety of applications. The dynamics between amoeba and R. solani were not studied as extensively, but the basic interaction is presented in the appendices of this thesis. Again, five amoeba species were incubated with mature R. solani mycelia. First, co-cultures were observed with a compound microscope. Acanthamoeba and Dictyostelium did not have any effect on the fungi. Acanthamoeba species physically associated with the mycelia, but also rapidly encysted – suggesting some antiprotozoal activity from R. solani. D. discoideum had no interaction with the fungi: the trophozoites did not attach to the mycelia and neither cysts nor spore-forming bodies were seen. V. vermiformis was the only amoeba with some effect on the fungi. In co-cultures, fungal mycelium developed a shriveled and wrinkled morphology. V. vermiformis was attached to the fungi and most amoebae remained as viable trophozoites. V. vermiformis and its interaction with R. solani was further examined using scanning electron microscopy, which further corroborated the light microscope observations. While the reason/effect of the shriveling is unknown, it is a potential avenue for further experiments. Also in the appendices are references to two published papers I co-authored. For more information, the two papers can be found in their respective open-access journals. | |
| dc.format.medium | born digital | |
| dc.format.medium | masters theses | |
| dc.identifier | Long_colostate_0053N_14818.pdf | |
| dc.identifier.uri | https://hdl.handle.net/10217/189430 | |
| dc.language | English | |
| dc.language.iso | eng | |
| dc.publisher | Colorado State University. Libraries | |
| dc.relation.ispartof | 2000-2019 | |
| dc.rights | Copyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright. | |
| dc.subject | phytobiome | |
| dc.subject | amoeba | |
| dc.subject | Xanthomonas | |
| dc.subject | Rhizoctonia | |
| dc.title | The interaction of free-living amoeba with rice bacterial and fungal pathogens | |
| dc.type | Text | |
| dcterms.rights.dpla | This Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). | |
| thesis.degree.discipline | Bioagricultural Sciences and Pest Management | |
| thesis.degree.grantor | Colorado State University | |
| thesis.degree.level | Masters | |
| thesis.degree.name | Master of Science (M.S.) |
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