Posttranscriptional Regulation of 2,4-Diacetylphloroglucinol Production by GidA and TrmE in Pseudomonas fluorescens 2P24

Abstract

Pseudomonas fluorescens 2P24 is a soilborne bacterium that synthesizes and excretes multiple antimicrobial metabolites. The polyketide compound 2,4-diacetylphloroglucinol (2,4-DAPG), synthesized by the phlACBD locus, is its major biocontrol determinant. This study investigated two mutants defective in antagonistic activity against Rhizoctonia solani. Deletion of the gidA (PM701) or trmE (PM702) gene from strain 2P24 completely inhibited the production of 2,4-DAPG and its precursors, monoacetylphloroglucinol (MAPG) and phloroglucinol (PG). The transcription of the phlA gene was not affected, but the translation of the phlA and phlD genes was reduced significantly. Two components of the Gac/Rsm pathway, RsmA and RsmE, were found to be regulated by gidA and trmE, whereas the other components, RsmX, RsmY, and RsmZ, were not. The regulation of 2,4-DAPG production by gidA and trmE, however, was independent of the Gac/Rsm pathway. Both the gidA and trmE mutants were unable to produce PG but could convert PG to MAPG and MAPG to 2,4-DAPG. Overexpression of PhlD in the gidA and trmE mutants could restore the production of PG and 2,4-DAPG. Taken together, these findings suggest that GidA and TrmE are positive regulatory elements that influence the biosynthesis of 2,4-DAPG posttranscriptionally.

RNA modification enzymes encoded by the gid operon: Implications in biology and virulence of bacteria

“…Inactivation of gidA has shown to slow the growth by approximately 10e20% in a number of bacteria like S. enterica, S. mutans, P. aeruginosa, A. hydrophila, and E. coli [11,16,17,33,58,60,64,70]. In contrast, studies in S. pyogenes and P. fluorescens have shown no difference between wild-type and gidA mutant growth [59,62]. This conflicting data, particularly amongst bacteria of the same genus, fails to suggest a common mechanism associated with GidA in bacterial growth.…”

“…Furthermore, their transcriptome analysis suggests a role for global regulation by GidA as seen in other Gram-negative bacteria [69]. Several reports show GidA-associated virulence mechanisms in several species of Pseudomonas [62,63,70]. The study by Kinscherf et al suggests a role for global regulation by GidA in Pseudomonas syringae.…”

“…This was an important discovery as P. aeruginosa is an opportunistic human pathogen that infects immunocompromised individuals using QS as a method to coordinate and regulate virulence gene expression [72e75]. Also in Pseudomonas, the study by Zhang et al showed a gidA deletion mutant was altered in QS gene expression and biofilm formation in Pseudomonas fluorescens [62]. Studies in other Gram-negative bacteria include the study by Yu et al which suggests GidA is a regulator of cytotoxic necrotizing factor 1 (CNF1), a major toxin in meningitis caused by E. coli K1 [67].…”

“…Additionally, many strains of P. fluorescens produce secondary antimicrobial metabolites which protect plants from a variety of diseases caused by soilborne pathogens [94]. A recent study by Zhang et al suggests GidA is a positive regulatory element that regulates the production of 2,4-diacetylphloroglucinol (2,4-DAPG) using a post-transcriptional mechanism [62]. In their study, a gidA deletion mutant was unable to produce phloroglucinol (PG), but could convert PG to monoacetylphloroglucinol (MAPG) and MAPG to 2,4 DAPG suggesting a pathway independent of the Gac/Rsm two-component system for the production of secondary antimicrobial metabolites [62].…”

“…A recent study by Zhang et al suggests GidA is a positive regulatory element that regulates the production of 2,4-diacetylphloroglucinol (2,4-DAPG) using a post-transcriptional mechanism [62]. In their study, a gidA deletion mutant was unable to produce phloroglucinol (PG), but could convert PG to monoacetylphloroglucinol (MAPG) and MAPG to 2,4 DAPG suggesting a pathway independent of the Gac/Rsm two-component system for the production of secondary antimicrobial metabolites [62]. This data suggests GidA is part of a major antimicrobial synthesis pathway in P. fluorescens, as 2,4-DAPG has antimicrobial activity against bacteria, viruses, and parasites [95,96].…”