Study of a fructose-negative mutant ofRhizobium meliloti

Abstract

Rhizobium meliloti grows on fructose as sole carbon source. Following nitrosoguanidine mutagenesis, a mutant of R. meliloti M5N1 was isolated as unable to grow on fructose. Enzyme assays with cell‐free extracts showed it to lack significative phosphoglucose isomerase activity. Other enzymes were present at low levels. Both fructose and fructose 6‐phosphate were accumulated within this mutant. The in vitro inhibition of fructokinase by fructose 6‐phosphate was show. Symbiotic properties remained unaffected in the mutant strain.

Agrobacterium radiobacter and related organisms take up fructose via a binding-protein-dependent active-transport system

“…transported fructose to fructose 6-phosphate and hence to glucose 6-phosphate have been detected in Rhixubitrm meliloti (Gardiol e t al., 1980;Guezzar et al, 1988), R. legtrminosartrm (Glenn e t al., 1984;McLaughlin & Hughes, 1989) and P. cepacia (Allenza et al, 1982), and the loss of one or other of these enzymes results in a failure to grow on fructose. These observations thus indicate that fructose is taken up via a high-affinity, active-transport system and is then converted to glucose 6-phosphate prior to metabolism via the Entner-Doudoroff pathway known to be present in these organisms (Gardiol e t al., 1980;Glenn et al, 1984;McLaughlin & Hughes, 1989).…”