Abstract
The expression of genes for S-adenosylmethionine synthetase (SAMS), which catalyzes the synthesis of S-adenosylmethionine (AdoMet), a major methyl donor in cells, was studied in symbiont-free (D) and symbiont-bearing (xD) amoeba strains to determine the effect of bacterial endosymbionts. The symbionts suppressed the expression of the gene in host xD amoebae, but amoebae still exhibited about half the enzyme activity found in symbiont-free D amoebae. The study was aimed at elucidating mechanisms of the suppression of the amoeba's gene and determining the alternative source for the gene product. Unexpectedly, we found a second sams (sams2) gene in amoebae, which encoded 390 amino acids. Results of experiments measuring SAMS activities and amounts of AdoMet in D and xD amoebae showed that the half SAMS activity found in xD amoebae came from the amoeba's SAMS2 and not from their endosymbionts. The expression of amoeba sams genes was switched from sams1 to sams2 as a result of infection with X-bacteria, raising the possibility that the switch in the expression of sams genes by bacteria plays a role in the development of symbiosis and the host-pathogen interactions. This is the first report showing such a switch in the expression of host sams genes by infecting bacteria.
Highlights
The xD strain of Amoeba proteus arose from the D strain by spontaneous infection of X-bacteria (Jeon and Lorch, 1967), and xD amoebae are dependent on their symbionts for survival
The expression of amoeba sams genes was switched from sams1 to sams2 as a result of infection with X-bacteria, raising the possibility that the switch in the expression of sams genes by bacteria plays a role in the development of symbiosis and the host-pathogen interactions
Even though X-bacteria had been completely compensation of S-adenosylmethionine synthetase (SAMS) or AdoMet by the symbionts, we first removed from xD amoebae by growing at 27°C, as checked checked growth rates of D and xD amoebae in media under a phase-contrast microscope, xD amoebae showed the supplemented with AdoMet, following the removal of X-bacteria by growing xD amoebae for 12 days at 27°C
Summary
The xD strain of Amoeba proteus arose from the D strain by spontaneous infection of X-bacteria (Jeon and Lorch, 1967), and xD amoebae are dependent on their symbionts for survival. Each xD amoeba contains about 42,000 symbionts within symbiosomes, and established xD amoebae die if their symbionts are removed. Infected xD amoebae become dependent on X-bacteria within 18 months (about 200 cell generations) (Jeon and Ahn, 1978), but the mechanism for the development of host dependence on their symbionts remains unknown. In their nucleotide sequences of GroEL genes (Ahn et al, 1994) and those of rRNA genes
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