Identification and occurrence of the hydroxamate siderophores aerobactin, putrebactin, avaroferrin and ochrobactin C as virulence factors from entomopathogenic bacteria

Abstract

Effective iron acquisition and fine-tuned intracellular iron storage systems are the main prerequisites for a successful host invasion by a pathogen. Bacteria have developed several different strategies to sequester this essential element from their environment, one relies on the secretion of low molecular weight compounds with high affinity for ferric iron, the so-called siderophores. Here, we report hydroxamate siderophore structures produced by entomopathogenic bacteria of the species Xenorhabdus and Photorhabdus, which are known for their potential to produce bioactive natural products, required for their role as nematode symbiont and insect pathogen. Four siderophores could be identified, namely aerobactin, putrebactin, avaroferrin and ochrobactin C, which was found previously only in marine bacteria. While the putrebactin and avaroferrin producing biosynthesis gene cluster (BGC) is more widespread and most likely was present in a common ancestor of these bacteria, the aerobactin and ochrobactin producing BGC was probably taken up by a few strains individually. For aerobactin a role in virulence towards Galleria mellonella larvae is shown.

Dissecting the Mechanism of Oligomerization and Macrocyclization Reactions of NRPS‐Independent Siderophore Synthetases

“…This led us to conclude that DesD shares with AvbD ar elaxeds ubstrate specificityf or different lengths of the diamino alkyl spacer and that product formation is again dictated via the availables ubstrate pool. Thisi si nl ine with resultsf rom the Codd group who reportedi ncorporation of an unsaturated HS [4]A precursor into desferrioxamine B. [16] Since both AvbD and DesD accept non-natural substrates, we reasoned that this promiscuity for synthetic substrates may provideameans to dissect and investigate the mechanism of type CN IS synthetases in greater detail.…”

“…For example, by the production of avaroferrin, Shewanella algae strain B516t hwarts iron piracy of Vibrio alginolyticus and inhibitsi ts swarming behavior. [19] Avaroferrin and putrebactin are also discussed as virulence factorsi ni nsectp athogenic bacteria [4] and bisucaberin may be associated with cold-water vibriosis of the fish pathogen Aliivibrio salmonicidae. [20] Desferrioxamines are widespread among environmental bacteria [21] and desferrioxamine Bi smarketed as Desferal, av aluabled rug against iron overloadw ith potential applications in antitumor therapy [22] and for treatment of Alzheimer's disease.…”

“…Surprisingly,A vbD and DesD exhibitedf or this substrate qualitativelyi dentical product profiles. Re-examining the reaction with HS [6]A revealed that in addition to the macrocyclict rimer [6+ +6+ +6] also large quantities of the dimeric macrocycle [6+ +6] were formed, while the native substrate HS [5]A gave with DesD exclusively the cyclic trimer [5+ +5+ +5] and with AvbD exclusively the cyclic dimer [5+ +5].W hen we incubated the shorter substrate HS [4]A with DesD, we also obtained the cyclic dimer [4+ +4] in considerable amounts, suggesting that affinity to the Cs ite and not merely length of the linear dimer determines the number of oligomerization steps. In contrast, HS [3]A did not yield any product with DesD( Figure S15), as has also been the case with AvbD.…”

“…[15] Structural changes in the N-terminus of the substrate thus have am ajor impact on the oligomerization steps carriedo ut by DesD but not on the iterativity of AvbD. While substrates closely relatedt ot he native one such as HS [4]A and HS [6]A still yieldedc yclic trimers with DesDf ollowed by smaller amountso fc yclic dimers,t he structurally more unrelated HS[8]A only gave cyclic dimer.T hese results confirm our model prediction that linear dimers of N-terminals ubstrate variants with native C-terminus may in DesD swap their affinity towards the Cs ite for the As ite, causing the cyclizationo fd imers. In contrast,f or AvbD which does not bind linear dimers in its C site the number of oligomerization steps remained unaffected.…”

A Systematic Analysis of Mosquito-Microbiome Biosynthetic Gene Clusters Reveals Antimalarial Siderophores that Reduce Mosquito Reproduction Capacity

“…In Shewanella algae , bisucaberin is simultaneously produced with avaroferrin and putrebactin via the same BGC and ratios of these compounds were controlled by substrate availability (Böttcher and Clardy, 2014; Rütschlin et al, 2017). Interestingly, entomopathogenic Xenorhabdus szentirmaii only produced putrebactin and avaroferrin (Hirschmann et al, 2017), while in our analysis of E. anophelis Ag1 only bisucaberin was detected, suggesting great diversity and fine control of the ratio of these siderophores by different species. Overall, all of the siderophores identified by MS were putatively assigned to a BGC ( Data Set S1E ) and then prioritized for bioactivity studies.…”