Minimum Requirements of Flagellation and Motility for Infection of Agrobacterium sp. Strain H13-3 by Flagellotropic Bacteriophage 7-7-1

Abstract

The flagellotropic phage 7-7-1 specifically adsorbs to Agrobacterium sp. strain H13-3 (formerly Rhizobium lupini H13-3) flagella for efficient host infection. The Agrobacterium sp. H13-3 flagellum is complex and consists of three flagellin proteins: the primary flagellin FlaA, which is essential for motility, and the secondary flagellins FlaB and FlaD, which have minor functions in motility. Using quantitative infectivity assays, we showed that absence of FlaD had no effect on phage infection, while absence of FlaB resulted in a 2.5-fold increase in infectivity. A flaA deletion strain, which produces straight and severely truncated flagella, experienced a significantly reduced infectivity, similar to that of a flaB flaD strain, which produces a low number of straight flagella. A strain lacking all three flagellin genes is phage resistant. In addition to flagellation, flagellar rotation is required for infection. A strain that is nonmotile due to an in-frame deletion in the gene encoding the motor component MotA is resistant to phage infection. We also generated two strains with point mutations in the motA gene resulting in replacement of the conserved charged residue Glu98, which is important for modulation of rotary speed. A change to the neutral Gln caused the flagellar motor to rotate at a constant high speed, allowing a 2.2-fold-enhanced infectivity. A change to the positively charged Lys caused a jiggly motility phenotype with very slow flagellar rotation, which significantly reduced the efficiency of infection. In conclusion, flagellar number and length, as well as speed of flagellar rotation, are important determinants for infection by phage 7-7-1.

Multiple Flagellin Proteins Have Distinct and Synergistic Roles inAgrobacterium tumefaciensMotility

“…The Δ flaA mutant produces straight, somewhat shortened filaments as evaluated by transmission electron microscopy (TEM, Fig. 1A), rather than producing stubs as reported in earlier studies (15). The Δ flaA mutant is also quite deficient in swimming through motility agar, although less so than an aflagellate Δ flgE hook mutant (Fig.…”

First Insights into the Entry Process of Hyperthermophilic Archaeal Viruses

“…Indeed, no retracting pili have been identified in archaea so far, which is also consistent with the apparent lack of genes encoding typical retraction ATPases in the archaeal pilus operons (52,53). A retraction-independent mechanism is utilized by flagellotrophic bacteriophages, which instead harness the energy of flagellar rotation to move along the flagellum toward the cell surface (14,16,17). Notably, the flagella (called archaella in archaea) of Sulfolobus are considerably thicker (ϳ14 nm in diameter [54]) than the LAL14/1 filaments to which SIRV2 binds.…”

“…A variety of cell surface structures are known to be targeted by viruses. For example, in the case of bacterial viruses, nearly all components of the cell envelope are known to serve as receptors (7), including lipopolysaccharide (8)(9)(10), pili (11)(12)(13), flagella (14)(15)(16)(17), (lipo-)teichoic acids (18)(19)(20), peptidoglycan (21), or various integral membrane proteins (22)(23)(24). The only archaeal virus for which a potential cellular receptor has been identified is Ch1, infecting the hyperhalophilic host Natrialba magadii (25).…”

Campylobacter jejuni Motility Is Required for Infection of the Flagellotropic Bacteriophage F341

“…A recent study on Agrobacterium sp. strain H13-3 flagellotropic phage 7-7-1 showed that different levels of motility greatly affected phage infection (73). A point mutation causing a change from the charged Glu98 to the neutral Gln of the motA gene led to hypermotility, resulting in more efficient phage infection (73).…”

“…Most studies of flagellotropic phages propose that the flagellum helps the attached phages to reach the basal body of the bacterium where DNA injection occurs (40)(41)(42)73), as phages with heads without DNA were observed only at the bacterial body (41). Phage was proposed to move to the base of its host during flagellar rotation by forcing the phage to follow the grooves formed by flagellin monomers "like a nut on a bolt" (42).…”