INDUCTION OF PHOSPHOLIPASE- AND FLAGELLAR SYNTHESIS IN SERRATIA-LIQUEFACIENS IS CONTROLLED BY EXPRESSION OF THE FLAGELLAR MASTER OPERON FLHD

When a liquid culture of Serratia spp. reaches the last part of the lo garithmic phase of growth it induces the synthesis of several extracel lular hydrolytic enzymes. In this communication we show that synthesis and secretion of the extracellular phospholipase is coupled to expres sion of flagella. Expression of flagella is demonstrated to follow a g rowth-phase-dependent pattern. Cloning, complementation studies and DN A-sequencing analysis has identified a genetic region in Serratia liqu efaciens which exhibits extensive homology to the Escherichia coli flh Dflagellar master operon. Interruption of the chromosomal flhDoperon i n S. liquefaciens results in non-flagellated and phospholipase-negativ e cells, but the synthesis of other exoenzymes is not affected. By pla cing the flhD operon under the control of a foreign inducible promoter we have shown that increased transcription through the flhD operon le ads to induction of flagellar synthesis and phospholipase expression.