Uptake of intact nucleoside monophosphates by Bdellovibrio bacteriovorus 109J

Abstract

The degraded nucleic acids and ribosomes of its prey cell provide Bdellovibrio bacteriovorus 109J with a source of ribonucleoside monophosphates and deoxyribonucleoside monophosphates for biosynthesis and respiration. We demonstrate that bdellovibrios, in contrast to almost all other bacteria, take up these nucleoside monophosphates into the cell in an intact, phosphorylated form. In this way they are able to assimilate more effectively the cellular contents of their prey. Studies with UMP and dTMP demonstrate that they are transported and accumulated against a concentration gradient, achieving internal levels at least 10 times the external levels. Treatment of the bdellovibrios with azide or carbonyl cyanide m-chlorophenylhydrazone eliminates their ability to either transport or maintain accumulated UMP and suggests the presence of a freely reversible exchange mechanism. There are at least two separate classes of transport systems for nucleoside monophosphates, each exhibiting partial specificity for either ribonucleoside monophosphates or deoxyribonucleoside monophosphates. Kinetic analyses of UMP transport in different developmental stages of strain 109J indicate that each stage expresses a single, saturable uptake system with a distinct apparent substrate affinity constant (Kt) of 104 microM in attack phase cells and 35 microM in prematurely released growth phase filaments. The capacity for transport of UMP by the growth phase filaments was 2.4 times that of the attack phase cells. These data, in addition to the apparent lack of environmental control of UMP transport capacity in attack phase cells, suggest that there are two transport systems for UMP in bdellovibrios and that the high-affinity, high-capacity growth phase system is developmentally regulated.