Cathelicidins in the Tasmanian devil (Sarcophilus harrisii)

Characterisation of defensins across the marsupial family tree

Defensins are antimicrobial peptides involved in innate immunity, and gene number differs amongst eutherian mammals. Few studies have investigated defensins in marsupials, despite their potential involvement in immunological protection of altricial young. Here we use recently sequenced marsupial genomes and transcriptomes to annotate defensins in nine species across the marsupial family tree. We characterised 35 alpha and 286 beta defensins; gene number differed between species, although Dasyuromorphs had the largest repertoire. Defensins were encoded in three gene clusters within the genome, syntenic to eutherians, and were expressed in the pouch and mammary gland. Marsupial beta defensins were closely related to eutherians, however marsupial alpha defensins were more divergent. We identified marsupial orthologs of human DEFB3 and 6, and several marsupial-specific beta defensin lineages which may have novel functions. Marsupial predicted mature peptides were highly variable in length and sequence composition. We propose candidate peptides for future testing to elucidate the function of marsupial defensins.

Multi-omics resources for the Australian southern stuttering frog (Mixophyes australis) reveal assorted antimicrobial peptides

The number of genome-level resources for non-model species continues to rapidly expand. However, frog species remain underrepresented, with up to 90% of frog genera having no genomic or transcriptomic data. Here, we assemble the first genomic and transcriptomic resources for the recently described southern stuttering frog (Mixophyes australis). The southern stuttering frog is ground-dwelling, inhabiting naturally vegetated riverbanks in south-eastern Australia. Using PacBio HiFi long-read sequencing and Hi-C scaffolding, we generated a high-quality genome assembly, with a scaffold N50 of 369.3 Mb and 95.1% of the genome contained in twelve scaffolds. Using this assembly, we identified the mitochondrial genome, and assembled six tissue-specific transcriptomes. We also bioinformatically characterised novel sequences of two families of antimicrobial peptides (AMPs) in the southern stuttering frog, the cathelicidins and β-defensins. While traditional peptidomic approaches to peptide discovery have typically identified one or two AMPs in a frog species from skin secretions, our bioinformatic approach discovered 12 cathelicidins and two β-defensins that were expressed in a range of tissues. We investigated the novelty of the peptides and found diverse predicted activities. Our bioinformatic approach highlights the benefits of multi-omics resources in peptide discovery and contributes valuable genomic resources in an under-represented taxon.

Tasmanian devil cathelicidins exhibit anticancer activity against Devil Facial Tumour Disease (DFTD) cells

The Tasmanian devil (Sarcophilus harrisii) is endangered due to the spread of Devil Facial Tumour Disease (DFTD), a contagious cancer with no current treatment options. Here we test whether seven recently characterized Tasmanian devil cathelicidins are involved in cancer regulation. We measured DFTD cell viability in vitro following incubation with each of the seven peptides and describe the effect of each on gene expression in treated cells. Four cathelicidins (Saha-CATH3, 4, 5 and 6) were toxic to DFTD cells and caused general signs of cellular stress. The most toxic peptide (Saha-CATH5) also suppressed the ERBB and YAP1/TAZ signaling pathways, both of which have been identified as important drivers of cancer proliferation. Three cathelicidins induced inflammatory pathways in DFTD cells that may potentially recruit immune cells in vivo. This study suggests that devil cathelicidins have some anti-cancer and inflammatory functions and should be explored further to determine whether they have potential as treatment leads.

Characterisation of the koala (Phascolarctos cinereus) pouch microbiota in a captive population reveals a dysbiotic compositional profile associated with neonatal mortality

BACKGROUND

Captive koala breeding programmes are essential for long-term species management. However, breeding efficacy is frequently impacted by high neonatal mortality rates in otherwise healthy females. Loss of pouch young typically occurs during early lactation without prior complications during parturition and is often attributed to bacterial infection. While these infections are thought to originate from the maternal pouch, little is known about the microbial composition of koala pouches. As such, we characterised the koala pouch microbiome across the reproductive cycle and identified bacteria associated with mortality in a cohort of 39 captive animals housed at two facilities.

RESULTS

Using 16S rRNA gene amplicon sequencing, we observed significant changes in pouch bacterial composition and diversity between reproductive time points, with the lowest diversity observed following parturition (Shannon entropy - 2.46). Of the 39 koalas initially sampled, 17 were successfully bred, after which seven animals lost pouch young (overall mortality rate - 41.18%). Compared to successful breeder pouches, which were largely dominated by Muribaculaceae (phylum - Bacteroidetes), unsuccessful breeder pouches exhibited persistent Enterobacteriaceae (phylum - Proteobacteria) dominance from early lactation until mortality occurred. We identified two species, Pluralibacter gergoviae and Klebsiella pneumoniae, which were associated with poor reproductive outcomes. In vitro antibiotic susceptibility testing identified resistance in both isolates to several antibiotics commonly used in koalas, with the former being multidrug resistant.

CONCLUSIONS

This study represents the first cultivation-independent characterisation of the koala pouch microbiota, and the first such investigation in marsupials associated with reproductive outcomes. Overall, our findings provide evidence that overgrowth of pathogenic organisms in the pouch during early development is associated with neonatal mortality in captive koalas. Our identification of previously unreported, multidrug resistant P. gergoviae strains linked to mortality also underscores the need for improved screening and monitoring procedures aimed at minimising neonatal mortality in future. Video Abstract.

SCMRSA: a New Approach for Identifying and Analyzing Anti-MRSA Peptides Using Estimated Propensity Scores of Dipeptides

Staphylococcus aureus is deemed to be one of the major causes of hospital and community-acquired infections, especially in methicillin-resistant S. aureus (MRSA) strains. Because antimicrobial peptides have captured attention as novel drug candidates due to their rapid and broad-spectrum antimicrobial activity, anti-MRSA peptides have emerged as potential therapeutics for the treatment of bacterial infections. Although experimental approaches can precisely identify anti-MRSA peptides, they are usually cost-ineffective and labor-intensive. Therefore, computational approaches that are able to identify and characterize anti-MRSA peptides by using sequence information are highly desirable. In this study, we present the first computational approach (termed SCMRSA) for identifying and characterizing anti-MRSA peptides by using sequence information without the use of 3D structural information. In SCMRSA, we employed an interpretable scoring card method (SCM) coupled with the estimated propensity scores of 400 dipeptides. Comparative experiments indicated that SCMRSA was more effective and could outperform several machine learning-based classifiers with an accuracy of 0.960 and Matthews correlation coefficient of 0.848 on the independent test data set. In addition, we employed the SCMRSA-derived propensity scores to provide a more in-depth explanation regarding the functional mechanisms of anti-MRSA peptides. Finally, in order to serve community-wide use of the proposed SCMRSA, we established a user-friendly webserver which can be accessed online at http://pmlabstack.pythonanywhere.com/SCMRSA. SCMRSA is anticipated to be an open-source and useful tool for screening and identifying novel anti-MRSA peptides for follow-up experimental studies.

Genomewide Analysis and Biological Characterization of Cathelicidins with Potent Antimicrobial Activity and Low Cytotoxicity from Three Bat Species

Cathelicidins are potent antimicrobial peptides with broad spectrum antimicrobial activity in many vertebrates and an important component of the innate immune system. However, our understanding of the genetic variations and biological characteristics of bat cathelicidins is limited. In this study, we performed genome-level analysis of the antimicrobial peptide cathelicidins from seven bat species in the six families, listed 19 cathelicidin-like sequences, and showed that the number of functional cathelicidin genes differed among bat species. Based on the identified biochemical characteristics of bat cathelicidins, three cathelicidins, HA-CATH (from Hipposideros armiger), ML-CATH (from Myotis lucifugus), and PD-CATH (from Phyllostomus discolor), with clear antimicrobial signatures were chemically synthesized and evaluated antimicrobial activity. HA-CATH showed narrow-spectrum antibacterial activity against a panel of 12 reference bacteria, comprising 6 Gram-negative and 6 Gram-positive strains. However, ML-CATH and PD-CATH showed potent antibacterial activity against a broad spectrum of Gram-negative and Gram-positive bacteria with minimum inhibitory concentration (MIC) of 1 and 3 μg/mL, respectively, against Staphylococcus aureus. ML-CATH and PD-CATH also showed antifungal activities against Candida albicans and Cryptococcus cuniculi with MIC of 5 to 40 μg/mL, respectively, and 80% inhibition of the metabolism of Mucor hiemalis hyphae at 80 μg/mL, while displaying minimal cytotoxicity to HaCaT cells. Taken together, although the spectrum and efficacy of bat cathelicidins were species-dependent, the antimicrobial activity of ML-CATH and PD-CATH was comparable to that of other highly active cathelicidins in vertebrates while having negligible cytotoxicity to mammalian cells. ML-CATH and PD-CATH can be exploited as promising candidates for the development of antimicrobial therapeutics.

Cathelicidin-3 Associated With Serum Extracellular Vesicles Enables Early Diagnosis of a Transmissible Cancer

The identification of practical early diagnostic biomarkers is a cornerstone of improved prevention and treatment of cancers. Such a case is devil facial tumor disease (DFTD), a highly lethal transmissible cancer afflicting virtually an entire species, the Tasmanian devil (Sarcophilus harrisii). Despite a latent period that can exceed one year, to date DFTD diagnosis requires visual identification of tumor lesions. To enable earlier diagnosis, which is essential for the implementation of effective conservation strategies, we analyzed the extracellular vesicle (EV) proteome of 87 Tasmanian devil serum samples using data-independent acquisition mass spectrometry approaches. The antimicrobial peptide cathelicidin-3 (CATH3), released by innate immune cells, was enriched in serum EV samples of both devils with clinical DFTD (87.9% sensitivity and 94.1% specificity) and devils with latent infection (i.e., collected while overtly healthy, but 3-6 months before subsequent DFTD diagnosis; 93.8% sensitivity and 94.1% specificity). Although high expression of antimicrobial peptides has been mostly related to inflammatory diseases, our results suggest that they can be also used as accurate cancer biomarkers, suggesting a mechanistic role in tumorous processes. This EV-based approach to biomarker discovery is directly applicable to improving understanding and diagnosis of a broad range of diseases in other species, and these findings directly enhance the capacity of conservation strategies to ensure the viability of the imperiled Tasmanian devil population.

Mammals' humoral immune proteins and peptides targeting the bacterial envelope: from natural protection to therapeutic applications against multidrug‐resistant Gram ‐negatives

Mammalian innate immunity employs several humoral ‘weapons’ that target the bacterial envelope. The threats posed by the multidrug‐resistant ‘ESKAPE’ Gram‐negative pathogens (Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) are forcing researchers to explore new therapeutic options, including the use of these immune elements. Here we review bacterial envelope‐targeting (peptidoglycan and/or membrane‐targeting) proteins/peptides of the mammalian immune system that are most likely to have therapeutic applications. Firstly we discuss their general features and protective activity against ESKAPE Gram‐negatives in the host. We then gather, integrate, and discuss recent research on experimental therapeutics harnessing their bactericidal power, based on their exogenous administration and also on the discovery of bacterial and/or host targets that improve the performance of this endogenous immunity, as a novel therapeutic concept. We identify weak points and knowledge gaps in current research in this field and suggest areas for future work to obtain successful envelope‐targeting therapeutic options to tackle the challenge of antimicrobial resistance.

A reference genome for the critically endangered woylie, Bettongia penicillata ogilbyi

Biodiversity is declining globally, and Australia has one of the worst extinction records for mammals. The development of sequencing technologies means that genomic approaches are now available as important tools for wildlife conservation and management. Despite this, genome sequences are available for only 5% of threatened Australian species. Here we report the first reference genome for the woylie (Bettongia penicillata ogilbyi), a critically endangered marsupial from Western Australia, and the first genome within the Potoroidae family. The woylie reference genome was generated using Pacific Biosciences HiFi long-reads, resulting in a 3.39 Gbp assembly with a scaffold N50 of 6.49 Mbp and 86.5% complete mammalian BUSCOs. Assembly of a global transcriptome from pouch skin, tongue, heart and blood RNA-seq reads was used to guide annotation with Fgenesh++, resulting in the annotation of 24,655 genes. The woylie reference genome is a valuable resource for conservation, management and investigations into disease-induced decline of this critically endangered marsupial.

Koala cathelicidin PhciCath5 has antimicrobial activity, including against Chlamydia pecorum

Devastating fires in Australia over 2019-20 decimated native fauna and flora, including koalas. The resulting population bottleneck, combined with significant loss of habitat, increases the vulnerability of remaining koala populations to threats which include disease. Chlamydia is one disease which causes significant morbidity and mortality in koalas. The predominant pathogenic species, Chlamydia pecorum, causes severe ocular, urogenital and reproductive tract disease. In marsupials, including the koala, gene expansions of an antimicrobial peptide family known as cathelicidins have enabled protection of immunologically naïve pouch young during early development. We propose that koala cathelicidins are active against Chlamydia and other bacteria and fungi. Here we describe ten koala cathelicidins, five of which contained full length coding sequences that were widely expressed in tissues throughout the body. Focusing on these five, we investigate their antimicrobial activity against two koala C. pecorum isolates from distinct serovars; MarsBar and IPTaLE, as well as other bacteria and fungi. One cathelicidin, PhciCath5, inactivated C. pecorum IPTaLE and MarsBar elementary bodies and significantly reduced the number of inclusions compared to the control (p<0.0001). Despite evidence of cathelicidin expression within tissues known to be infected by Chlamydia, natural PhciCath5 concentrations may be inadequate in vivo to prevent or control C. pecorum infections in koalas. PhciCath5 also displayed antimicrobial activity against fungi and Gram negative and positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Electrostatic interactions likely drive PhciCath5 adherence to the pathogen cell membrane, followed by membrane permeabilisation leading to cell death. Activity against E. coli was reduced in the presence of 10% serum and 20% whole blood. Future modification of the PhciCath5 peptide to enhance activity, including in the presence of serum/blood, may provide a novel solution to Chlamydia infection in koalas and other species.

Host reproductive cycle influences the pouch microbiota of wild southern hairy-nosed wombats (Lasiorhinus latifrons)

Background

Marsupials are born much earlier than placental mammals, with most crawling from the birth canal to the protective marsupium (pouch) to further their development. However, little is known about the microbiology of the pouch and how it changes throughout a marsupial’s reproductive cycle. Here, using stringent controls, we characterized the microbial composition of multiple body sites from 26 wild Southern Hairy-nosed Wombats (SHNWs), including pouch samples from animals at different reproductive stages.

Results

Using qPCR of the 16S rRNA gene we detected a microbial community in the SHNW pouch. We observed significant differences in microbial composition and diversity between the body sites tested, as well as between pouch samples from different reproductive stages. The pouches of reproductively active females had drastically lower microbial diversity (mean ASV richness 19 ± 8) compared to reproductively inactive females (mean ASV richness 941 ± 393) and were dominated by gram positive bacteria from the Actinobacteriota phylum (81.7–90.6%), with the dominant families classified as Brevibacteriaceae, Corynebacteriaceae, Microbacteriaceae, and Dietziaceae. Three of the five most abundant sequences identified in reproductively active pouches had closest matches to microbes previously isolated from tammar wallaby pouches.

Conclusions

This study represents the first contamination-controlled investigation into the marsupial pouch microbiota, and sets a rigorous framework for future pouch microbiota studies. Our results indicate that SHNW pouches contain communities of microorganisms that are substantially altered by the host reproductive cycle. We recommend further investigation into the roles that pouch microorganisms may play in marsupial reproductive health and joey survival.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-021-00074-8.

The Value of Reference Genomes in the Conservation of Threatened Species

Conservation initiatives are now more crucial than ever-over a million plant and animal species are at risk of extinction over the coming decades. The genetic management of threatened species held in insurance programs is recommended; however, few are taking advantage of the full range of genomic technologies available today. Less than 1% of the 13505 species currently listed as threated by the International Union for Conservation of Nature (IUCN) have a published genome. While there has been much discussion in the literature about the importance of genomics for conservation, there are limited examples of how having a reference genome has changed conservation management practice. The Tasmanian devil (Sarcophilus harrisii), is an endangered Australian marsupial, threatened by an infectious clonal cancer devil facial tumor disease (DFTD). Populations have declined by 80% since the disease was first recorded in 1996. A reference genome for this species was published in 2012 and has been crucial for understanding DFTD and the management of the species in the wild. Here we use the Tasmanian devil as an example of how a reference genome has influenced management actions in the conservation of a species.

Identification of novel antimicrobial peptide from Asian sea bass (Lates calcarifer) by in silico and activity characterization

Background

The global crisis of antibiotic resistance increases the demand for the new promising alternative drugs such as antimicrobial peptides (AMPs). Accordingly, we have described a new, previously unrecognized effective AMP, named dicentracin-like, from Asian sea bass and characterized its antimicrobial activity by comparison with moronecidin.

Methodology/ Results

Gene expression analysis demonstrated the expression of dicentracin-like peptide in tissues of the immune system such as the skin and the head kidney, which is an important endocrine and lymphoid organ. Moronecidin and dicentracin-like exhibited a higher antibacterial activity against gram-positive bacteria relative to gram-negative ones, while both peptides showed a greater binding ability to gram-negative bacteria compared to gram-positive ones. This contradiction between antibacterial activity and binding affinity may be related to the outer membrane from gram-negative bacteria. Compared with moronecidin, dicentracin-like peptide showed more potent binding ability to all gram-positive and gram-negative bacteria. In addition, dicentracin-like peptide exhibited a high antibacterial activity against the investigated microorganisms, except against Staphylococcus aureus. A direct relationship was found between the binding affinity/cationicity and the antibiofilm activity of the peptides wherein, an elevation in pH corresponded to a decrease in their antibiofilm property. Time-kill kinetics analysis against clinical Acinetobacter baumannii isolate indicated that bactericidal effect of dicentracin-like and moronecidin at inhibitory concentration (1XMIC) was observed after 4 and 6 hours, respectively, while bactericidal effect of both AMPs at concentration of 2XMIC was observed after 2 hours. Dicentracin-like peptide showed higher inhibitory activity at subinhibitory concentration (1/2XMIC), relative to moronecidin. Compared with moronecidin, dicentracin-like peptide possessed greater binding affinity to bacteria at high salt concentration, as well as at alkaline pH; In addition, dicentracin-like exhibited a higher antibiofilm activity in comparison to moronecidin even at alkaline pH. Hemolytic analysis against human RBC revealed that hemolytic activity of moronecidin was more potent than that of dicentracin-like, which is consistent with its greater non-polar face hydrophobicity.

Conclusions

In the present study, In Silico comparative sequence analysis and antimicrobial characterization led to identify a new, previously unrecognized antimicrobial function for named dicentracin-like peptide by comparison with moronecidin, representing a possible template for designing new effective AMPs and improving known ones.

Lessons learnt from the Tasmanian devil facial tumour regarding immune function in cancer

Genetic and genomic technologies have facilitated a greater understanding of the Tasmanian devil immune system and the origins, evolution and spread of devil facial tumour disease (DFTD). DFTD is a contagious cancer that has caused significant declines in devil populations across Tasmania. Immune responses to DFTD are rarely detected, allowing the cancer to pass between individuals and proliferate unimpeded. Early immunosenscence in devils appears to decrease anti-tumour immunity in older animals compared to younger animals, which may increase susceptibility to DFTD and explain high DFTD prevalence in this age group. Devils also have extremely low major histocompatibility complex (MHC) diversity, and multiple alleles are shared with the tumour, lowering histocompatibility barriers which may have contributed to DFTD evolution. DFTD actively evades immune attack by down-regulating cell-surface MHC I molecules, making it effectively invisible to the immune system. Altered MHC I profiles should activate natural killer (NK) cell anti-tumour responses, but these are absent in DFTD infection. Recent immunisation and immunotherapy using modified DFTD cells has induced an anti-DFTD immune response and regression of DFTD in some devils. Knowledge gained from immune responses to a transmissible cancer in devils will ultimately reveal useful insights into immunity to cancer in humans and other species.

Combined Antimicrobial Activity of Photodynamic Inactivation and Antimicrobials-State of the Art

Antimicrobial photodynamic inactivation (aPDI) is a promising tool for the eradication of life-threatening pathogens with different profiles of resistance. This study presents the state-of-the-art published studies that have been dedicated to analyzing the bactericidal effects of combining aPDI and routinely applied antibiotics in in vitro (using biofilm and planktonic cultures) and in vivo experiments. Furthermore, the current paper reviews the methodology used to obtain the published data that describes the synergy between these antimicrobial approaches. The authors are convinced that even though the combined efficacy of aPDI and antimicrobials could be investigated with the wide range of methods, the use of a unified experimental methodology that is in agreement with antimicrobial susceptibility testing (AST) is required to investigate possible synergistic cooperation between aPDI and antimicrobials. Conclusions concerning the possible synergistic activity between the two treatments can be drawn only when appropriate assays are employed. It must be noticed that some of the described papers were just aimed at determination if combined treatments exert enhanced antibacterial outcome, without following the standard methodology to evaluate the synergistic effect, but in most of them (18 out of 27) authors indicated the existence of synergy between described antibacterial approaches. In general, the increase in bacterial inactivation was observed when both therapies were used in combination.

Marsupial and monotreme cathelicidins display antimicrobial activity, including against methicillin-resistant Staphylococcus aureus

With the growing demand for new antibiotics to combat increasing multi-drug resistance, a family of antimicrobial peptides known as cathelicidins has emerged as potential candidates. Expansions in cathelicidin-encoding genes in marsupials and monotremes are of specific interest as the peptides they encode have evolved to protect immunologically naive young in the harsh conditions of the pouch and burrow. Our previous work demonstrated that some marsupial and monotreme cathelicidins have broad-spectrum antibacterial activity and kill resistant bacteria, but the activity of many cathelicidins is unknown. To investigate associations between peptide antimicrobial activity and physiochemical properties, we tested 15 cathelicidin mature peptides from tammar wallaby, grey short-tailed opossum, platypus and echidna for antimicrobial activity against a range of bacterial and fungal clinical isolates. One opossum cathelicidin ModoCath4, tammar wallaby MaeuCath7 and echidna Taac-CATH1 had broad-spectrum antibacterial activity and killed methicillin-resistant Staphylococcus aureus. However, antimicrobial activity was reduced in the presence of serum or whole blood, and non-specific toxicity was observed at high concentrations. The active peptides were highly charged, potentially increasing binding to microbial surfaces, and contained amphipathic helical structures, which may facilitate membrane permeabilisation. Peptide sequence homology, net charge, amphipathicity and alpha helical content did not correlate with antimicrobial activity. However active peptides contained a significantly higher percentage of cationic residues than inactive ones, which may be used to predict active peptides in future work. Along with previous studies, our results indicate that marsupial and monotreme cathelicidins show potential for development as novel therapeutics to combat increasing antimicrobial resistance.

Antimicrobial Protection of Marsupial Pouch Young

Marsupials diverged from eutherian mammals about 148 million years ago and represent a unique lineage of mammals with distinctive morphological and reproductive characteristics. Marsupials have significantly shorter gestation periods than eutherians. Pregnancy typically ranges from 15 to 35 days, with young being born at a very early developmental stage and lacking differentiated lymphoid tissues and mature effector cells. Recent microbiome studies of the marsupial pouch revealed that marsupial young can face intense microbial challenges after birth, as the pouch contains a broad range of Gram-positive and Gram-negative bacteria. Antimicrobials are believed to play a significant role in the immune protection of marsupial newborns during their pouch life. The skin of the post-reproductive pouch secretes antimicrobial lysozyme and dermcidin, which may contribute to the decreased density of certain bacteria in the pouch. A range of antimicrobial agents, such as immunoglobulins, lysozyme, transferrin, and cathelicidins, have been identified in marsupial milk. Antimicrobial assays have revealed that marsupial cathelicidins have broad-spectrum activity against a variety of bacteria and fungi, including several multi-drug resistant strains. In this article, we will review the action mechanisms of these antimicrobial compounds and discuss how they protect marsupial newborns from potentially pathogenic bacteria inside the pouch. We will also discuss the potential of marsupial antimicrobial compounds as a source of novel antibiotics.

Characterization of the antimicrobial peptide family defensins in the Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus), and tammar wallaby (Macropus eugenii)

Defensins comprise a family of cysteine-rich antimicrobial peptides with important roles in innate and adaptive immune defense in vertebrates. We characterized alpha and beta defensin genes in three Australian marsupials: the Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus), and tammar wallaby (Macropus eugenii) and identified 48, 34, and 39 defensins, respectively. One hundred and twelve have the classical antimicrobial peptides characteristics required for pathogen membrane targeting, including cationic charge (between 1+ and 15+) and a high proportion of hydrophobic residues (>30%). Phylogenetic analysis shows that gene duplication has driven unique and species-specific expansions of devil, koala, and tammar wallaby beta defensins and devil alpha defensins. Defensin genes are arranged in three genomic clusters in marsupials, whereas further duplications and translocations have occurred in eutherians resulting in four and five gene clusters in mice and humans, respectively. Marsupial defensins are generally under purifying selection, particularly residues essential for defensin structural stability. Certain hydrophobic or positively charged sites, predominantly found in the defensin loop, are positively selected, which may have functional significance in defensin-target interaction and membrane insertion.