Development of Host's Dependence on Intracellular Symbionts

宿主对细胞内共生体的依赖性的发展

• 批准号: 9727911
• 负责人: Kwang W. Jeon
• 金额: $ 21万
• 依托单位: University of Tennessee Knoxville
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-06-01 至 2002-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9727911&HistoricalAwards=false
• 关键词: Development; Host; Dependence; Intracellular; Symbionts

9727911 Jeon The long-term goals of the proposed study are to elucidate the mechanisms whereby infecting microbes enter host cells and survive inside the latter, some of them becoming integrated as intracellular symbionts. Such integration may result in the acquisition of new cell components for a host cell. The objectives of the current project to determine how infecting X-bacteria enter amoebae and survive inside the latter, eventually becoming integrated as intracellular symbionts. In symbiosis between amoebae and X-bacteria, host amoebae are dependent on symbionts for survival and newly infected amoebae become dependent on symbionts within 18 months (about 200 cell generations). Thus, for amoebae, the integrated X-bacteria become new cell components. Two important and outstanding questions are 1) how infecting bacteria avoid destruction by their host cells and 2) why or how amoebae become dependent on bacterial symbionts for survival. While some insights to the first question were gained from previous studies, it was only recent that a viable clue to the second question was found: X-bacteria prevent the production of an essential enzyme by amoebae, but then supply the enzyme through an alternate route. Symbiont-bearing xD amoebae no longer produce an enzyme that functions as S-adenosylmethionine synthetase (SAMS) in symbiont-free D amoebae. The absence of SAMS in xD amoebae is attributable to xD amoeba's failure to transcribe the corresponding gene as a result of harboring bacterial symbionts. These results showed how symbiotic X-bacteria might cause their hosts to become dependent on them. In the proposed study, the following hypotheses will be tested: 1) That X-bacteria suppress the expression of an amoeba's housekeeping gene, sams, but X-bacteria supply the gene product, SAMS, so that amoebae become dependent on symbionts in time. The PIs have two monoclonal antibodies against the SAMS of amoebae to use in our studies. 2) That X-bacteria-produced protein(s) or a protein enco ded by a plasmid inside X-bacteria acts as a regulatory factor to suppress the expression of the sams gene in xD amoebae. These studies will involve the use of techniques such as DNA cloning, nucleotide sequencing, site-directed mutagenesis and genomic footprinting. The expected results from these studies will provide further insight into mechanisms for the general evasion of host destruction by infective microbes and their subsequent survival. The results will also enhance the elucidation of mechanism for the establishment and maintenance of stable endosymbiosis leading to the acquisition of new cell components in eukaryotic cells.

9727911 Jeon 拟议研究的长期目标是阐明感染微生物进入宿主细胞并在宿主细胞内存活的机制，其中一些微生物整合为细胞内共生体。 这种整合可能导致宿主细胞获得新的细胞成分。 当前项目的目标是确定感染性 X 细菌如何进入阿米巴原虫并在后者体内存活，最终整合为细胞内共生体。 在阿米巴原虫和X细菌的共生中，宿主阿米巴原虫依赖共生体生存，新感染的阿米巴原虫在18个月内（大约200个细胞代）变得依赖共生体。 因此，对于阿米巴原虫来说，整合的X细菌成为新的细胞成分。 两个重要且悬而未决的问题是：1）感染细菌如何避免被宿主细胞破坏；2）变形虫为何或如何依赖细菌共生体生存。 虽然从之前的研究中获得了对第一个问题的一些见解，但直到最近才发现第二个问题的可行线索：X-细菌阻止阿米巴原虫产生必需酶，但随后通过替代途径提供酶。 带有共生体的 xD 变形虫不再产生一种在无共生体的 D 变形虫中起 S-腺苷甲硫氨酸合成酶 (SAMS) 作用的酶。 xD变形虫中SAMS的缺失是由于xD变形虫由于携带细菌共生体而无法转录相应的基因。 这些结果表明，共生 X 细菌可能如何导致宿主对它们产生依赖。 在拟议的研究中，将测试以下假设：1）X细菌抑制阿米巴变形虫管家基因sams的表达，但X细菌提供基因产物SAMS，从而使变形虫及时变得依赖于共生体。 PI 有两种针对变形虫 SAMS 的单克隆抗体，可用于我们的研究。 2) X-细菌产生的蛋白质或由X-细菌内的质粒编码的蛋白质作为调节因子抑制xD变形虫中sams基因的表达。 这些研究将涉及 DNA 克隆、核苷酸测序、定点诱变和基因组足迹等技术的使用。 这些研究的预期结果将进一步深入了解感染性微生物普遍逃避宿主破坏的机制及其随后的生存。 这些结果还将增强对稳定内共生的建立和维持的机制的阐明，从而导致在真核细胞中获得新的细胞成分。