Biosynthesis of the antifungal haterumalide, oocydin A, in Serratia, and its regulation by quorum sensing, RpoS and Hfq

Abstract

Polyketides represent an important class of bioactive natural products with a broad range of biological activities. We identified recently a large trans-acyltransferase (AT) polyketide synthase gene cluster responsible for the biosynthesis of the antifungal, anti-oomycete and antitumor haterumalide, oocydin A (ooc). Using genome sequencing and comparative genomics, we show that the ooc gene cluster is widespread within biocontrol and phytopathogenic strains of the enterobacteria, Serratia and Dickeya. The analysis of in frame deletion mutants confirmed the role of a hydroxymethylglutaryl-coenzyme A synthase cassette, three flavin-dependent tailoring enzymes, a free-standing acyl carrier protein and two hypothetical proteins in oocydin A biosynthesis. The requirement of the three trans-acting AT domains for the biosynthesis of the macrolide was also demonstrated. Expression of the ooc gene cluster was shown to be positively regulated by an N-acyl-L-homoserine lactone-based quorum sensing system, but operating in a strain-dependent manner. At a post-transcriptional level, the RNA chaperone, Hfq, plays a key role in oocydin A biosynthesis. The Hfq-dependent regulation is partially mediated by the stationary phase sigma factor, RpoS, which was also shown to positively regulate the synthesis of the macrolide. Our results reveal differential regulation of the divergently transcribed ooc transcriptional units, highlighting the complexity of oocydin A production.

A Polyketide Synthase Component for Oxygen Insertion into Polyketide Backbones

“…Oocydin-type polyketides,w hich include haterumalides and biselides (Table 2), are known from diverse biological Communications sources comprising various marine ascidians, [18] sponges, [19] and bacteria. [11,17,20] Several of the invertebrate-derived haterumalides (4,19,20) [18c, 19,21] and biselides (21)(22) [18a, b, 21] feature ester or amide moieties instead of the proposed OocK-derived carboxylate unit at C19 of oocydinA (4). In light of our results,w es peculated that some of these congeners might be uncleaved precursors.T op redict the precursor of 4,weanalyzed the domain architecture of OocJ, which has no counterpart in the polyketide structure (Figure 4).…”

“…Interestingly,P edG-like proteins appear in other PKS systems,b ut the polyketides do not necessarily feature hydroxy termini like in 1.T oi nvestigate the prevalence of oxygenation in these systems and their corresponding products,w ep hylogenetically analyzed sequences of PedG-like proteins and related homologues of flavindependent monooxygenases ( Figure 2). In this analysis, PedG forms ad istinct clade with 29 oxygenases,i ncluding those from trans-ATP KSs for the pederin-like compound diaphorin (3)f rom ap syllid symbiont, [10] for oocydin A( 4) from S. plymuthica 4Rx13, [11] and for the methylobacterial toblerol A( 5). [12] Another member of the clade is the myxobacterial AmbI from the cis-ATP KS ambruticin (6) pathway,a ne nzyme suggested to be involved in adecarboxylative hydroxylation.…”

Biosynthesis of the acetyl‐CoA carboxylase‐inhibiting antibiotic, andrimid in Serratia is regulated by Hfq and the LysR‐type transcriptional regulator, AdmX

“…Serratia plymuthica strains are near‐ubiquitous in nature but have been commonly isolated from soil and the rhizosphere of many economically important crops (De Vleesschauwer and Höfte, 2007). Serratia plymuthica strains possess great potential as biocontrol agents by antagonizing the growth of plant‐pathogens through the production of diverse bioactive secondary metabolites, siderophores and lytic enzymes (Alström, ; De Vleesschauwer and Höfte, 2007; Matilla et al ., ). The strain used in this study, Serratia plymuthica A153, was isolated from the rhizosphere of wheat (Åstrom and Gerhardson, ) and it has been shown to possess bioactivity against fungi, oomycetes, bacteria and nematodes (Thaning et al ., ; Matilla et al ., ; Hellberg et al ., ).…”

“…As a result, the synthesis of the cognate secondary metabolite can be modulated appropriately. Quorum sensing regulatory circuits (Coulthurst et al ., ; Williamson et al ., ; Müller et al ., ; Matilla et al ., ), two‐component systems (Sola‐Landa et al ., ; Haas and Défago, ; Williamson et al ., ), orphan transcriptional regulators (Williamson et al ., ; Lu et al ., ; Klaponski et al ., ) and post‐transcriptional regulators (Vogel and Luisi, ; Romeo et al ., ) can all be involved in the regulatory complexity of bacterial secondary metabolite control.…”

Genome Sequence of the Oocydin A-Producing Rhizobacterium Serratia plymuthica 4Rx5

“…More recently, strain 4Rx5 has been used as a model bacterium for the investigation of biosynthesis and regulation of the antifungal oocydin A (8). In contrast to other oocydin A-producing strains, the biosynthesis of this polyketide in 4Rx5 was shown to be regulated by an N -acyl- l -homoserine lactone-based quorum-sensing-system (8). Additionally, 4Rx5 was shown to produce chitinases and proteases (1) and siderophores (M. A. Matilla and G. P. C. Salmond, unpublished data).…”