Biological Role of Paenilarvins, Iturin-Like Lipopeptide Secondary Metabolites Produced by the Honey Bee Pathogen Paenibacillus larvae

Abstract

The Gram-positive bacterium Paenibacillus larvae (P. larvae) is the causative agent of a deadly honey bee brood disease called American Foulbrood (AFB). AFB is a notifiable epizootic in most countries and, hence, P. larvae is of considerable relevance for veterinarians and apiculturists alike. Over the last decade, much progress has been made in the understanding of the (patho)biology of P. larvae. Recently, several non-ribosomally produced peptides (NRP) and peptide/polyketide (NRP/PK) hybrids produced by P. larvae were identified. Among these NRPs were iturin-like lipopeptides, the paenilarvins A-C. Iturins are known to exhibit strong anti-fungal activity; for some iturins, cytotoxic activity towards mammalian erythrocytes and human cancer cell lines are described. We here present our results on the analysis of the natural function of the paenilarvins during pathogenesis of P. larvae infections. We demonstrated production of paenilarvins in infected larvae. However, we could neither demonstrate cytotoxicity of paenilarvins towards cultured insect cells nor towards larvae in feeding assays. Accordingly, exposure bioassays performed with larvae infected by wild-type P. larvae and a knockout mutant of P. larvae lacking production of paenilarvins did not substantiate a role for the paenilarvins as virulence factor. Further experiments are necessary to analyze the relevance of the paenilarvins’ anti-fungal activity for P. larvae infections in the presence of fungal competitors in the larval midgut or cadaver.

Genome Mining of the Lipopeptide Biosynthesis of Paenibacillus polymyxa E681 in Combination with Mass Spectrometry: Discovery of the Lipoheptapeptide Paenilipoheptin

“…This result is consistent with our mass spectrometry data of paenilipoheptins. Interestingly, Paenibacillus larvae , a honey bee pathogen inducing the American foulbrood, produces a family of lipoheptapeptides, the paenilarvins, which are directly related to iturins …”

“…Interestingly, Paenibacillus larvae,ahoney bee pathogen inducing the Americanf oulbrood, produces af amily of lipoheptapeptides, the paenilarvins,w hicha re directly related to iturins. [29,30] Cyclic lipoheptapeptides are frequently used motifs of Bacillales. Well known are the heptapeptide compounds surfactins and iturins produced by numerous B. subtilis and B. amyloliquefaciens strains [50,51] that exhibit manifold valuable activities, such as antimicrobial, antiviral, and antimycoplasmatic effects, which qualify them for both medical and biotechnological applications.…”

“…Our work is particularly focusedo nt he hybrid Nrps-Trans-AT-PKS gene clusterC(2 569 478-2 611964), which encodes the biosynthesis of ay et-unknownl ipoheptapeptide product, the genes of which show 50 %s imilarity to the paenilarvin gene cluster (BGC0000402_c1). [29,30] The existence of such ac ompound was recently predicted by genome minings tudies performed by Aleti et al [6] and Xie et al, [7] but its specific nature and structure have remained unresolved. Cluster Cc omprises seven amino-acid activating and condensing modules.…”

Characterization of the toxin Plx2A, a RhoA‐targeting ADP‐ribosyltransferase produced by the honey bee pathogen Paenibacillus larvae

“…These results led to a better understanding of the virulence differences and showed that the two genotypes follow different molecular strategies during the invasive phase of infection (Djukic et al ., ; Poppinga and Genersch, ). Differential production of several secondary metabolites was demonstrated (Garcia‐Gonzalez et al ., ; Hertlein et al ., ; Müller et al ., ; Sood et al ., ) including paenilamicin, which is produced by P. larvae ERIC II only and was shown to suppress the growth of bacterial competitors in the larval gut (Müller et al ., ; Müller et al ., ). A key virulence factor of both P. larvae ERIC I and ERIC II is Pl CBP49, a chitin‐degrading enzyme responsible for the destruction of the peritrophic matrix during infection (Garcia‐Gonzalez and Genersch, ; Garcia‐Gonzalez et al ., ).…”

Proteinase pattern of honeybee prepupae from healthy and American Foulbrood infected bees investigated by zymography

“…Moreover, P. larvae produces some antibacterial peptides against competing microorganisms: Paenilamicins acts against bacteria and Paenilarvin acts against fungal competitors .…”