title: Phenotypic and Physiological Characterization of the Epibiotic Interaction Between TM7x and Its Basibiont Actinomyces.
abstract: Despite many examples of obligate epibiotic symbiosis (one organism living on the surface of another) in nature, such an interaction has rarely been observed between two bacteria. Here, we further characterize a newly reported interaction between a human oral obligate parasitic bacterium TM7x (cultivated member of Candidatus Saccharimonas formerly Candidate Phylum TM7), and its basibiont Actinomyces odontolyticus species (XH001), providing a model system to study epiparasitic symbiosis in the domain Bacteria. Detailed microscopic studies indicate that both partners display extensive morphological changes during symbiotic growth. XH001 cells manifested as short rods in monoculture, but displayed elongated and hyphal morphology when physically associated with TM7x. Interestingly, these dramatic morphological changes in XH001 were also induced in oxygen-depleted conditions, even in the absence of TM7x. Targeted quantitative real-time PCR (qRT-PCR) analyses revealed that both the physical association with TM7x as well as oxygen depletion triggered up-regulation of key stress response genes in XH001, and in combination, these conditions act in an additive manner. TM7x and XH001 co-exist with relatively uniform cell morphologies under nutrient-replete conditions. However, upon nutrient depletion, TM7x-associated XH001 displayed a variety of cell morphologies, including swollen cell body, clubbed-ends, and even cell lysis, and a large portion of TM7x cells transformed from ultrasmall cocci into elongated cells. Our study demonstrates a highly dynamic interaction between epibiont TM7x and its basibiont XH001 in response to physical association or environmental cues such as oxygen level and nutritional status, as reflected by their morphological and physiological changes during symbiotic growth.
authors.affiliation: Section of Oral Biology, School of Dentistry, University of California, Los Angeles, CA, 90095, USA.
authors.forename: Batbileg
authors.initials: B
authors.lastname: Bor
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA, 90095, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Poweleit
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, MC 114-96, Pasadena, CA, 91125, USA.
authors.forename: Justin S
authors.initials: JS
authors.lastname: Bois
authors.affiliation: Section of Oral Biology, School of Dentistry, University of California, Los Angeles, CA, 90095, USA.
authors.forename: Lujia
authors.initials: L
authors.lastname: Cen
authors.affiliation: Section of Oral Biology, School of Dentistry, University of California, Los Angeles, CA, 90095, USA.
authors.forename: Joseph K
authors.initials: JK
authors.lastname: Bedree
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA, 90095, USA.|California Nanosystems Institute, University of California, Los Angeles, CA, 90095, USA.
authors.forename: Z Hong
authors.initials: ZH
authors.lastname: Zhou
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA, 90095, USA.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Gunsalus
authors.affiliation: Section of Oral Biology, School of Dentistry, University of California, Los Angeles, CA, 90095, USA.
authors.forename: Renate
authors.initials: R
authors.lastname: Lux
authors.affiliation: Department of Periodontics, University of Washington, Seattle, WA, 98195, USA.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: McLean
authors.affiliation: Section of Oral Biology, School of Dentistry, University of California, Los Angeles, CA, 90095, USA. xhe@g.ucla.edu.
authors.forename: Xuesong
authors.initials: X
authors.lastname: He
authors.affiliation: Section of Oral Biology, School of Dentistry, University of California, Los Angeles, CA, 90095, USA. wenyuan@ucla.edu.
authors.forename: Wenyuan
authors.initials: W
authors.lastname: Shi
mesh_terms: D000190:Actinomyces / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology*; D001419:Bacteria / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification; D018407:Bacterial Physiological Phenomena; D006801:Humans; D009055:Mouth / Q000382:microbiology*; D010641:Phenotype; D013559:Symbiosis
keywords: Actinomyces; Bacterial interaction; Epibiont; Obligate; Symbiosis; TM7