Thermoregulation of N -Acyl Homoserine Lactone-Based Quorum Sensing in the Soft Rot Bacterium Pectobacterium atrosepticum

Abstract

The psychrotolerant bacterium Pectobacterium atrosepticum produces four N-acyl homoserine lactones under a wide range of temperatures. Their thermoregulation differs from that of the exoenzyme production, described as being under quorum-sensing control. A mechanism involved in this thermoregulation consists of controlling N-acyl homoserine lactones synthase production at a transcriptional level.Several gram-negative bacteria synthesize N-acyl homoserine lactone (HSL) signal molecules that serve for cell-to-cell communication called for the first time quorum sensing (QS) by Fuqua et al. (7). Such regulatory systems operate to allow bacteria to sense cell density and to synchronize the functions of the entire population (reviewed in references 15, 23, and 29). In the Pectobacterium atrosepticum species (formerly Erwinia carotovora subsp. atroseptica) (8), QS regulation is involved in pectinolytic, cellulase, and protease activities, tuber maceration, and harpin synthesis leading to a hypersensitive response in nonhost plant (18,25). In contrast, QS via HSL production does not regulate growth and mobility during initial infection events or during liquid culture in a synthetic medium (25).Pectobacterium atrosepticum is a psychrotrophic bacterium involved in the soft rot of Solanum tuberosum (17, 26). Consequently, it causes important losses within cool temperate regions, where potatoes have traditionally been grown. The optimal temperature for pathogenicity, estimated to be around 20°C (19, 21), is a good compromise allowing both a fast multiplication (optimal at 24°C) and an efficient production of lytic enzymes, which is optimal at temperatures ranging between 12 and 24°C (26). As the thermoregulation of bacterial multiplication differs from that of exoenzyme production, we investigated the thermoregulation of QS that triggers exoenzyme synthesis. Therefore, HSL production and accumulation were measured during the three growth phases of a typical P. atrosepticum strain (Table 1) cultured at six temperatures. The role of the expI gene encoding the HSL synthase was determined by cloning this gene in Escherichia coli and by engineering a mutated strain of P. atrosepticum. Finally, the transcription of expI was estimated by relative reverse transcription-PCR (RT-PCR) under the same range of temperatures.Effect of temperature on N-acyl HSL diversity and levels. Bacterial cultures were grown at 8,12,15,20,24, and 28°C in minimal medium with polygalacturonic acid (PGA) as the sole source of carbon. This vegetable compound induces synthesis of virulence factors involved in plant disease or resistance that have been demonstrated to be under QS control (25). Characterization of HSLs was performed by high-performance liquid chromatography coupled with mass spectrometry (16). In these conditions, P. atrosepticum 6276 produces four HSLs: mainly N-3-oxo-octanoyl-L-HSL (3-oxo-C8-HSL) and minor quantities of N-octanoyl-L-HSL (C8-HSL), N-3-oxo-hexanoyl-L-HSL (3-oxo-C6-HSL), and N-3-oxo-decanoyl-L-HSL (3-oxo-C10-HSL). The HSL level...

Quorum Sensing Signaling Molecules Produced by Reference and Emerging Soft-Rot Bacteria (Dickeya and Pectobacterium spp.)

“…If the NAHSL production appears to be directly linked to the NAHSL synthase expression, the AI-2 one seems rather under the control of the activated methyl cycle and the SAM synthase expression. Nevertheless, we confirm the hypothesis that one of the mechanisms involved in the regulation of Pectobacterium AI-1 QS consists of controlling NAHSL synthase production by modulating the amounts of luxI transcripts [13]. Another outcome of the present work is that AI-2 and IAA signaling pathways do not seem to act simultaneously.…”

Transcriptome of the quorum-sensing signal-degrading Rhodococcus erythropolis responds differentially to virulent and avirulent Pectobacterium atrosepticum

“…When P. atrosepticum interacts with potato plants, two phases can be discerned: an asymptomatic colonization phase, which may occur along the vegetative development of the plant host, followed by a symptomatic phase, in which the blackleg and soft-rot diseases are expressed (Pirhonen et al, 1993;Smadja et al, 2004;Latour et al, 2007;Liu et al, 2008). On the basis of our results on the 3-partner interaction, we postulate a differential response of the biocontrol agent R. erythropolis during both phases of the interaction of P. atrosepticum on potato.…”

Contribution of the Pseudomonas fluorescens MFE01 Type VI Secretion System to Biofilm Formation

“…tumefaciens NT1 biosensors. Pectobacterium atrosepticum 6276 Δexp1 , impaired in C8-AHL production, was included as a negative control [45]. …”