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Journal of Bacteriology, August 2004, p. 4986-4993, Vol. 186, No. 15
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.15.4986-4993.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

The Global Regulator Genes from Biocontrol Strain Serratia plymuthica IC1270: Cloning, Sequencing, and Functional Studies

Marianna Ovadis,^1, Xiaoguang Liu,^2, Sagi Gavriel,¹ Zafar Ismailov,³ Ilan Chet,⁴ and Leonid Chernin^1*

Otto Warburg Center for Biotechnology in Agriculture, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem,¹ Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel,⁴ Department of Plant Pathology, Shandong Agricultural University, Tai'an 271018, Shandong, China,² Department of Genetics and Biotechnology, Faculty of Biology, Samarkand State University, Samarkand 703004, Republic of Uzbekistan³

Received 29 February 2004/ Accepted 26 April 2004

The biocontrol activity of various fluorescent pseudomonads towards plant-pathogenic fungi is dependent upon the GacA/GacS-type two-component system of global regulators and the RpoS transcription sigma factor. In particular, these components are required for the production of antifungal antibiotics and exoenzymes. To investigate the effects of these global regulators on the expression of biocontrol factors by plant-associated bacteria other than Pseudomonas spp., gacA/gacS and rpoS homologues were cloned from biocontrol strain IC1270 of Serratia plymuthica, which produces a set of antifungal compounds, including chitinolytic enzymes and the antibiotic pyrrolnitrin. The nucleotide and deduced protein sequence alignments of the cloned gacA/gacS-like genes—tentatively designated grrA (global response regulation activator) and grrS (global response regulation sensor) and of the cloned rpoS gene revealed 64 to 93% identity with matching genes and proteins of the enteric bacteria Escherichia coli, Pectobacterium carotovora subsp. carotovora, and Serratia marcescens. grrA, grrS, and rpoS gene replacement mutants of strain IC1270 were deficient in the production of pyrrolnitrin, an exoprotease, and N-acylhomoserine lactone quorum-sensing signal molecules. However, neither mutant appeared to differ from the parental strain in the production of siderophores, and only grrA and grrS mutants were deficient in the production of a 58-kDa endochitinase, representing the involvement of other sigma factors in the regulation of strain IC1270's chitinolytic activity. Compared to the parental strain, the grrA, grrS, and rpoS mutants were markedly less capable of suppressing Rhizoctonia solani and Pythium aphanidermatum under greenhouse conditions, indicating the dependence of strain IC1270's biocontrol property on the GrrA/GrrS and RpoS global regulators.

Supplemental material for this article may be found at http://jb.asm.org/.

The first two authors contributed equally to this work.

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