Regulated breakdown of Escherichia coli deoxyribonucleic acid during intraperiplasmic growth of Bdellovibrio bacteriovorus 109J

Abstract

During growth of Bdellovibrio bacteriovorus on [2-"C]deoxythymidine-labeled Escherichia coli, approximately 30% of the radioactivity was released to the culture fluid as nucleoside monophosphates and free bases; the remainder was incorporated by the bdellovibrio. By 60 min after bdellovibrio attack, when only 10% of the E. coli deoxyribonucleic acid (DNA) had been solubilized, the substrate cell DNA was degraded to 5 x 105-dalton fragments retained within the bdelloplast. Kinetic studies showed these fragments were formed as the result of sequential accumulation of singleand then double-strand cuts. DNA fragments between 2 x 103 and 5 x 105 daltons were never observed. Chloramphenicol, added at various times after initiation of bdellovibrio intraperiplasmic growth on normal or on heated E. coli, which have inactivated deoxyribonucleases, inhibited further breakdown and solubilization of substrate cell DNA. Analysis of these intraperiplasmic culture deoxyribonuclease activities showed that bdellovibrio deoxyribonucleases are synthesized while E. coli nucleases are inactivated. It is concluded that continuous and sequential synthesis of bdellovibrio deoxyribonucleases of apparently differing specificities is necessary for complete breakdown and solubilization of substrate cell DNA, and that substrate cell deoxyribonucleases are not involved in any significant way in the degradation process. MATERIALS AND METHODSGrowth and harvesting of cells. B. bacteriovorus 109J was the experimental organism, and normal or heated [2-'4C]deoxythymidine-labeled E. coli ML35 620 on July 31, 2020 by guest

Comparative biology of intracellular parasitism.

“…Some host macromolecules, notably several outer membrane proteins (99), may be transferred intact from host to bdellovibrio, but most often host polymers are broken down to monomers at rates consistent with the synthetic needs of the parasite. For example, host DNA is split into 500-kilodalton pieces by an endonuclease, and then an exonuclease hydrolyzes off deoxyribonucleoside monophosphates which are incorporated directly into parasite DNA (259,351). Similar mechanisms probably exist for breakdown and resynthesis of RNA and protein (184).…”

Molecular parasitism in the Escherichia coli-Bdellovibrio bacteriovorus system: translocation of the matrix protein from the host to the parasite outer membrane.

“…It is actively motile and after adsorption onto the host, a specific enzyme(s) is induced in the parasite (Varon and Shilo, 1968). Maturation begins when the parasite penetrates through the outer membrane into the host periplasm where, -60 min later, synthesis of B. bacteriovorus DNA begins (Matin and Rittenberg, 1972; Rosson and Rittenberg, 1979). The parasite causes shut-off of the host macromolecular synthetic apparatus, and is able to grow on host cells killed by various agents, including antibiotics (Varon et al, 1969;Rittenberg and Shilo, 1970).…”

Ribonucleotide reductases and their occurrence in microorganisms: A link to the RNA/DNA transition

“…occurs only in the host cell after invasion into the periplasmic space. Experiments with [3H]thymidine labelled E. coli showed that host DNA is degraded by bdellovibrio deoxyribonucleases and incorporated into bdellovibrio DNA [111,112]. Exogenous thymidine monophosphates compete effectively with labelled host DNA; low incorporation rates of thymidine argue for a deficiency of deoxynucleoside kinases [113].…”