Occurrence and distribution of unsubstituted B-ring flavanones in Eucalyptus foliage

Preliminary Study on Total Component Analysis and In Vitro Antitumor Activity of Eucalyptus Leaf Residues

Eucalyptus globulus is widely introduced and cultivated in Yunnan province. Its foliage is mainly used to extract eucalyptus oil, but the by-product eucalyptus residue has not been fully utilized. Based on the above reasons, in this study, we sought to explore the comprehensive utilization potential of eucalyptus resources. The total composition of eucalyptus residue was analyzed by ultra performance liquid chromatography-time-of-flight mass spectrometry (UPLC-Q/TOF MS), and the active components and nutrient components of eucalyptus leaf residue were determined by chemical methods and liquid phase techniques. Meanwhile, the antitumor activity of triterpenoids in eucalyptus leaves was evaluated by tetramethylazazole blue colorimetric assay (MTT). The results of qualitative analysis indicated that 55 compounds were identified from eucalyptus residue, including 28 phloroglucinols, 17 terpenoids, 3 flavonoids, 5 fatty acids, 1 amino acid and 2 polyphenols. Among them, the pentacyclic triterpenoids, in eucalyptus residue, were mainly oleanane type and urthane type. The results of quantitative determination indicated that the content of triterpenoid compounds was 2.84% in eucalyptus residue, which could be enhanced to 82% by silicone separation. The antitumor activity results showed that triterpenoid compounds have moderate inhibitory effects on human breast cancer cell MDA-MB-231, gastric adenocarcinoma cell SGC-7901 and cervical cancer cell Hela. The half maximal inhibitory concentration (IC50) was 50.67, 43.12 and 42.65 μg/mL, respectively. In this study, the triterpenoids from eucalyptus leaf residues were analyzed to reveal that the triterpenoids from eucalyptus leaf have antitumor effects and have potential to be developed as antitumor drugs.

Individuality and stability of the koala (Phascolarctos cinereus) faecal microbiota through time

Gut microbiota studies often rely on a single sample taken per individual, representing a snapshot in time. However, we know that gut microbiota composition in many animals exhibits intra-individual variation over the course of days to months. Such temporal variations can be a confounding factor in studies seeking to compare the gut microbiota of different wild populations, or to assess the impact of medical/veterinary interventions. To date, little is known about the variability of the koala (Phascolarctos cinereus) gut microbiota through time. Here, we characterise the gut microbiota from faecal samples collected at eight timepoints over a month for a captive population of South Australian koalas (n individuals = 7), and monthly over 7 months for a wild population of New South Wales koalas (n individuals = 5). Using 16S rRNA gene sequencing, we found that microbial diversity was stable over the course of days to months. Each koala had a distinct faecal microbiota composition which in the captive koalas was stable across days. The wild koalas showed more variation across months, although each individual still maintained a distinct microbial composition. Per koala, an average of 57 (±16) amplicon sequence variants (ASVs) were detected across all time points; these ASVs accounted for an average of 97% (±1.9%) of the faecal microbial community per koala. The koala faecal microbiota exhibits stability over the course of days to months. Such knowledge will be useful for future studies comparing koala populations and developing microbiota interventions for this regionally endangered marsupial.

The koala gut microbiome is largely unaffected by host translocation but rather influences host diet

Introduction

Translocation is a valuable and increasingly used strategy for the management of both threatened and overabundant wildlife populations. However, in some instances the translocated animals fail to thrive. Differences in diet between the source and destination areas may contribute to poor translocation outcomes, which could conceivably be exacerbated if the animals' microbiomes are unsuited to the new diet and cannot adapt.

Methods

In this study we tracked how the faecal microbiome of a specialist Eucalyptus folivore, the koala (Phascolarctos cinereus), changed over the course of a year after translocation. We assessed microbiome composition by 16S rRNA amplicon sequencing of faecal pellets.

Results

We found no significant overall changes in the faecal microbiomes of koalas post-translocation (n = 17) in terms of microbial richness, diversity or composition when compared to the faecal microbiomes of koalas from an untranslocated control group (n = 12). This was despite the translocated koalas feeding on a greater variety of Eucalyptus species after translocation. Furthermore, while differences between koalas accounted for half of the microbiome variation, estimated diets at the time of sampling only accounted for 5% of the variation in the koala microbiomes between sampling periods. By contrast, we observed that the composition of koala faecal microbiomes at the time of translocation accounted for 37% of between koala variation in post-translocation diet. We also observed that translocated koalas lost body condition during the first month post-translocation and that the composition of the koalas' initial microbiomes were associated with the magnitude of that change.

Discussion

These findings suggest that the koala gut microbiome was largely unaffected by dietary change and support previous findings suggesting that the koala gut microbiome influences the tree species chosen for feeding. They further indicate that future research is needed to establish whether the koalas' gut microbiomes are directly influencing their health and condition or whether aspects of the koala gut microbiomes are an indicator of underlying physiological differences or pathologies. Our study provides insights into how animal microbiomes may not always be affected by the extreme upheaval of translocation and highlights that responses may be host species-specific. We also provide recommendations to improve the success of koala translocations in the future.

Warmer Ambient Temperatures Depress Detoxification and Food Intake by Marsupial Folivores

Ambient temperature is an underappreciated determinant of foraging behaviour in wild endotherms, and the requirement to thermoregulate likely influences food intake through multiple interacting mechanisms. We investigated relationships between ambient temperature and hepatic detoxification capacity in two herbivorous marsupials, the common ringtail possum (Pseudocheirus peregrinus) and common brushtail possum (Trichosurus vulpecula) that regularly feed on diets rich in plant toxins. As an indicator of hepatic detoxification capacity, we determined the functional clearance rate of an anaesthetic agent, Alfaxalone, after possums were acclimated to 10°C [below the thermoneutral zone (TNZ)], 18°C [approximately lower critical temperature (LCT)], and 26°C [approximately upper critical temperature (UCT)] for either 7 days or less than 24 h. We then measured intake of foods with high or low plant secondary metabolite (PSM) concentrations under the same temperature regimes. After 7 days of acclimation, we found a positive correlation between the functional clearance rate of Alfaxalone and ambient temperature, and a negative relationship between ambient temperature and intake of foods with high or low PSM concentrations for both species. The effect of ambient temperature on intake of diets rich in PSMs was absent or reduced when possums were kept at temperatures for less than 24 h. Our results underscore the effects of ambient temperature in hepatic metabolism particularly with respect intake of diets containing PSMs. Given that the planet is warming, it is vital that effects of ambient temperature on metabolism, nutrition and foraging by mammalian herbivores is taken into account to predict range changes of species and their impact on ecosystems.

Chemical diversity of kānuka: Inter- and intraspecific variation of foliage terpenes and flavanones of Kunzea (Myrtaceae) in Aotearoa/New Zealand

Kunzea (Myrtaceae) trees and shrubs, generally called kānuka, grow across most of Aotearoa/New Zealand (NZ). With the exception of K. sinclairii, an offshore island endemic, kānuka had been treated as an Australasian species K. ericoides. However, a 2014 taxonomic revision recognized ten species, all endemic to NZ. Kānuka chemistry is less studied than that of its closest relative in NZ, mānuka (Leptospermum scoparium), which shows very distinct regional foliage chemotypes. We have used a miniaturized method with GC and ¹H NMR to analyze foliage chemistry of voucher specimens from across the geographic ranges of the ten NZ Kunzea species. We found common mono- and sesquiterpenes, with α-pinene dominant in all samples, but only traces of antimicrobial triketones. Two unusual flavanones, with unsubstituted B-rings and known bioactivity against Phytophthora, did distinguish some of the samples. 5,7-Dihydroxy-6,8-dimethyl flavanone was only found at high concentrations in the three K. sinclairii samples in this study's sample set, but this compound has separately been reported in K. robusta samples from a nearby region. Therefore none of the NZ Kunzea species was distinguished by the chemistry analyzed in this study, but there is a possibility of regional flavonoid chemotypes cutting across the species boundaries.

Molecular Characterisation of Flavanone O-methylation in Eucalyptus

Flavonoids are ubiquitous polyphenolic compounds in plants, long recognised for their health-promoting properties in humans. Methylated flavonoids have received increasing attention due to the potential of methylation to enhance medicinal efficacy. Recently, Eucalyptus species with high levels of the O-methylated flavanone pinostrobin have been identified. Pinostrobin has potential commercial value due to its numerous pharmacological and functional food benefits. Little is known about the identity or mode of action of the enzymes involved in methylating flavanones. This study aimed to identify and characterise the methyltransferase(s) involved in the regiospecific methylation of pinostrobin in Eucalyptus and thereby add to our limited understanding of flavanone biosynthesis in plants. RNA-seq analysis of leaf tips enabled the isolation of a gene encoding a flavanone 7-O-methyltransferase (EnOMT1) in Eucalyptus. Biochemical characterisation of its in vitro activity revealed a range of substrates upon which EnOMT1 acts in a regiospecific manner. Comparison to a homologous sequence from a Eucalyptus species lacking O-methylated flavonoids identified critical catalytic amino acid residues within EnOMT1 responsible for its activity. This detailed molecular characterisation identified a methyltransferase responsible for chemical ornamentation of the core flavanone structure of pinocembrin and helps shed light on the mechanism of flavanone biosynthesis in Eucalyptus.

Characterization of the juvenile koala gut microbiome across wild populations

In this study we compared the faecal microbiomes of wild joey koalas (Phascolarctos cinereus) to those of adults, including their mothers, to establish whether gut microbiome maturation and inheritance in the wild is comparable to that seen in captivity. Our findings suggest that joey koala microbiomes slowly shift towards an adult assemblage between 6 and 12 months of age, as the microbiomes of 9-month-old joeys were more similar to those of adults than those of 7-month-olds, but still distinct. At the phylum level, differences between joeys and adults were broadly consistent with those in captivity, with Firmicutes increasing in relative abundance over the joeys' development and Proteobacteria decreasing. Of the fibre-degrading genes that increased in abundance over the development of captive joeys, those involved in hemicellulose and cellulose degradation, but not pectin degradation, were also generally found in higher abundance in adult wild koalas compared to 7-month-olds. Greater maternal inheritance of the faecal microbiome was seen in wild than in captive koalas, presumably due to the more solitary nature of wild koalas. This strong maternal inheritance of the gut microbiome could contribute to the development of localized differences in microbiome composition, population health and diet through spatial clustering of relatives.

Mapping canopy nitrogen-scapes to assess foraging habitat for a vulnerable arboreal folivore in mixed-species Eucalyptus forests

Herbivore foraging decisions are closely related to plant nutritional quality. For arboreal folivores with specialized diets, such as the vulnerable greater glider (Petauroides volans), the abundance of suitable forage trees can influence habitat suitability and species occurrence. The ability to model and map foliar nitrogen would therefore enhance our understanding of folivore habitat use at finer scales. We tested whether high-resolution multispectral imagery, collected by a lightweight and low-cost commercial unoccupied aerial vehicle (UAV), could be used to predict total and digestible foliar nitrogen (N and digN) at the tree canopy level and forest stand-scale from leaf-scale chemistry measurements across a gradient of mixed-species Eucalyptus forests in southeastern Australia. We surveyed temperate Eucalyptus forests across an elevational and topographic gradient from sea level to high elevation (50-1200 m a.s.l.) for forest structure, leaf chemistry, and greater glider occurrence. Using measures of multispectral leaf reflectance and spectral indices, we estimated N and digN and mapped N and favorable feeding habitat using machine learning algorithms. Our surveys covered 17 Eucalyptus species ranging in foliar N from 0.63% to 1.92% dry matter (DM) and digN from 0.45% to 1.73% DM. Both multispectral leaf reflectance and spectral indices were strong predictors for N and digN in model cross-validation. At the tree level, 79% of variability between observed and predicted measures of nitrogen was explained. A spatial supervised classification model correctly identified 80% of canopy pixels associated with high N concentrations (≥1% DM). We developed a successful method for estimating foliar nitrogen of a range of temperate Eucalyptus species using UAV multispectral imagery at the tree canopy level and stand scale. The ability to spatially quantify feeding habitat using UAV imagery allows remote assessments of greater glider habitat at a scale relevant to support ground surveys, management, and conservation for the vulnerable greater glider across southeastern Australia.

Fundamental dietary specialisation explains differential use of resources within a koala population

The diets of individual animals within populations can differ, but few studies determine whether this is due to fundamental differences in preferences or capacities to eat specific foods, or to external influences such as dominance hierarchies or spatial variation in food availability. The distinction is important because different drivers of dietary specialisation are likely to have different impacts on the way in which animal populations respond to, for example, habitat modification. We used a captive feeding study to investigate the mechanisms driving individual dietary specialisation in a population of wild koalas (Phascolarctos cinereus) in which individuals predominantly ate either Eucalyptus viminalis or Eucalyptus obliqua foliage. All six koalas that primarily ate E. viminalis in the wild avoided eating E. obliqua for more than 1 month in captivity. In contrast, all seven koalas that primarily ate E. obliqua could be maintained exclusively on this species in captivity, although they ate less from individual trees with higher foliar concentrations of unsubstituted B-ring flavanones (UBFs). Our results show that fundamental differences between individual animals allow some to exploit food resources that are less suitable for others. This could reduce competition for food, increase habitat carrying capacity, and is also likely to buffer the population against extinction in the face of habitat modification. The occurrence of fundamental individual specialisation within animal populations could also affect the perceived conservation value of different habitats, translocation or reintroduction success, and population dynamics. It should therefore be further investigated in other mammalian herbivore species.

The distribution and abundance of an unusual resource for koalas (Phascolarctos cinereus) in a sodium-poor environment

Environmentally available sodium tends to decrease with increasing elevation, and sodium resources in these sodium-poor environments are critical for the survival of herbivores. Eucalypt leaves in the subalpine Monaro region of NSW, Australia contain much less sodium than eucalypt leaves at lower elevations, and subalpine koalas obtain this much needed resource by eating the bark from some Eucalyptus mannifera trees. To better understand the availability of salty-barked trees, we searched for evidence of koala bark chewing at 100 randomly generated locations in the region. We found 318 E. mannifera trees with koala chew marks. We also analysed sodium concentrations in the bark of three unchewed E. mannifera trees from each site to determine whether there were trees with high bark sodium content that had not yet been utilized by koalas. Although 90% of unchewed trees had sodium concentrations less than 225.4 mg.kg-1 DM, some unchewed trees contained high sodium concentrations (up to 1213.1 mg.kg-1 DM). From the random survey, we can extrapolate that 11% of trees in this area have bark sodium above 300 mg.kg-1 DM, which is based on the concentration of bark sodium observed in at least moderately chewed trees. We would expect to find 0.24 of these trees per 200 m2, or 720,000 salty-barked trees in the 30 km by 20 km study area. Bark chewing by koalas is widespread in the area, and trees with salty bark are more common than initially thought. We discuss correlations with the occurrence of salty-barked trees and other landscape attributes; however, questions remain about why some E. mannifera trees have much more bark sodium than others. Studies such as this one should be expanded to identify sodium resources and their availability for other herbivorous species, since many are predicted to move to higher elevations in response to climate change.

Faecal inoculations alter the gastrointestinal microbiome and allow dietary expansion in a wild specialist herbivore, the koala

Background

Differences between individuals in their gastrointestinal microbiomes can lead to variation in their ability to persist on particular diets. Koalas are dietary specialists, feeding almost exclusively on Eucalyptus foliage but many individuals will not feed on particular Eucalyptus species that are adequate food for other individuals, even when facing starvation. We undertook a faecal inoculation experiment to test whether a koala’s gastrointestinal (GI) microbiome influences their diet. Wild-caught koalas that initially fed on the preferred manna gum (Eucalyptus viminalis) were brought into captivity and orally inoculated with encapsulated material derived from faeces from koalas feeding on either the less preferred messmate (E. obliqua; treatment) or manna gum (control).

Results

The gastrointestinal microbiomes of wild koalas feeding primarily on manna gum were distinct from those feeding primarily on messmate. We found that the gastrointestinal microbiomes of koalas were unresponsive to dietary changes because the control koalas’ GI microbiomes did not change even when the nocturnal koalas were fed exclusively on messmate overnight. We showed that faecal inoculations can assist the GI microbiomes of koalas to change as the treatment koalas’ GI microbiomes became more similar to those of wild koalas feeding on messmate. There was no overall difference between the control and treatment koalas in the quantity of messmate they consumed. However, the greater the change in the koalas’ GI microbiomes, the more messmate they consumed after the inoculations had established.

Conclusions

The results suggest that dietary changes can only lead to changes in the GI microbiomes of koalas if the appropriate microbial species are present, and/or that the koala gastrointestinal microbiome influences diet selection.

Electronic supplementary material

The online version of this article (10.1186/s42523-019-0008-0) contains supplementary material, which is available to authorized users.