Host Promiscuity Research Articles

First Report of Fusarium luffae Causing Leaf Blight on Loquat in Eastern China.

During May-June 2021 and 2022, leaf blight symptoms were observed on loquat leaves (Eriobotrya japonica cv. 'Mogi') in Jiangsu Province (Xuzhou municipality, 117.17° E, 34.13° N) in China. Approximately 10% of the leaves on the two hundred trees studied in a six-year-old loquat orchard exhibited round lesions that changed from light yellow to reddish-brown in 8-10 days. Approximately 3% of the infected leaves exhibited numerous lesions that coalesced, leading to expansive blighted areas. Twenty-five samples of symptomatic tissue, approximately 0.2 cm2 in size, were collected in May 2022 from five different trees (five samples per tree), sterilized in 2% NaOCl for 1 min, washed twice with sterilized ddH2O, and incubated at 26°C for 5 days on PDA medium containing 50 µg/mL chloramphenicol. Six isolates were obtained via single spore isolation. ITS (OQ954852-OQ954857), TUB2 (OQ968488-OQ968493), EF1-α (OQ971890-OQ971895), RPB1 (OQ971896-OQ971901), and RPB2 (OR037266-OR037271) genes were amplified using the ITS1/ITS4, T1/T22, EF1-728F/EF1-986R, RPB1-R8/RPB1-F5, and fRPB2-7CF/fRPB2-11aR primers, respectively (O'Donnell et al. 2010). The species was identified using the Fusarioid ID database (Crous et al. 2021), revealing that all obtained isolates showed high homology to representative F. luffae strains. Upon combining the ITS, TUB2, EF1-α, RPB1, and RPB2 sequences, the isolates showed 99.42%-97.85% and 99.59%-98.10% identity to F. luffae CGMCC 3.19497 (ex-type strain) and NRRL 32522, respectively. A molecular phylogenetic tree was constructed using MEGA X, with a selection of representative Fusarium strains. Microscope observations showed septate mycelium, microconidia (6.86 ± 0.91 µm length, 1.67 ± 0.24 µm width, containing 1 septum; number of observations = 21), fusiform macroconidia (15.88 ± 1.43 µm length, 1.66 ± 0.24 µm width, containing 1 septum; number of observations = 45), and linear chlamydospores (79.36 ± 28.36 µm length, 12.03 ± 3.37 µm width; number of observations = 152). These observations are consistent with the morphology of F. luffae (Wang et al. 2019). All isolates exhibited identical morphological characteristics. All isolates were evaluated for pathogenicity in vivo using healthy non-detached loquat leaves. A total of 15 leaves from 5 different three-month-old 'Mogi' loquat trees were used for each isolate. Experiments were performed three times. A suspension of 1 × 106 spores/mL obtained from a seven-day-old colony (10 mL per 15 leaves), was sprayed on non-wounded leaves for inoculation. Sterilized ddH2O was used in the control experiment. Inoculated trees were stored at 26°C and 70% relative humidity for four days. Leaf blight symptoms were observed in all inoculated leaves, and the symptoms were observed in all repeated trials. The pathogen was recovered, and its identity was confirmed by ITS sequencing and morphological analysis, fulfilling Koch's postulates. In recent years, F. luffae has been reported to cause fruit rot on muskmelon, flower rot on kiwifruit, soybean pod rot, and leaf spot on cherry in China (Yu et al. 2022; Zhang et al. 2022; Zhao et al. 2022; Zhou et al. 2022), demonstrating the host promiscuity of this pathogen. Although F. solani has been identified as the causal agent of root rot and fruit rot on loquat (Abbas et al. 2017; Wu et al. 2021), this is the first report of F. luffae causing leaf blight on loquat worldwide. This report will help to understand the pathogens affecting loquat orchards in China.

First Report of Bacterial Leaf Blight caused by Enterobacter asburiae on Sorghum in Jiangsu Province, China.

Sorghum (Sorghum bicolor [L.] Moench) is a major cereal crop in China, with a planting area of more than 674666 ha in 2021. In August 2022, bacterial leaf blight symptoms were observed on sorghum plants grown in a field in Huai'an (119.30437 ºE, 33.999644 ºN), in Jiangsu Province (Fig. 1). To determine the causal agent, four symptomatic leaves from different plants were surface sterilized with 75% (v/v) ethanol for 1 min and washed three times with ddH2O. The surface-sterilized plant tissues were cut into small pieces (4 × 4 mm in size) and cultured on Nutrient Agar (NA) plates at 28ºC for 24 h. To obtain pure cultures, these colonies were transferred to fresh NA plates by using the conventional streak plate method. The purified bacterial cells were rod-shaped, from 1.14 to 1.66 μm long, and from 0.61 to 0.86 μm wide (number of observations = 31) (Fig. 2). Three isolates were used for further characterization. The Gram stain test indicated that the three isolates were Gram negative. 16S rRNA (27F/1492R primers) and gyrB (UP1/Up2r) genes were amplified and sequenced (Marchesi et al. 1998; Yamamoto and Harayama 1995). The obtained 16S rRNA (0R143361-0R143363) and gyrB sequences (0R146993-0R146995) were submitted to GenBank. The 16S rRNA sequences of the three isolated strains showed over 98% identity (1447/1462, 1438/1462 and 1443/1460 bp) to the E. asburiae reference strains ENIPBJ CG1, CAV1043 and 1808 013 (CP014993.1, CP011591.1 and AP019632.1, respectively). Similarly, the gyrB sequences of the three strains showed 98% identity (1103/1129, 1105/1129 and 1108/1129 bp) to the same E. asburiae reference strains. Four-week-old sorghum plants were used in the pathogenicity tests. A phylogenetic tree was constructed with reference strains (Hoffmann et al., 2005). The healthy leaves were inoculated with bacterial suspensions of the three bacterial isolates (OD600 = 0.6~1.0) using the leaf cutting method (Kauffman et al. 1973). For the control group, sterilized ddH2O was used. Each isolate was inoculated in three healthy plants. Inoculated plants were incubated at 28ºC and 75% humidity with alternating 12-h light and 12-h dark cycles with a photon flux density of 200 mmol/m2/s. After 10 days, bacterial leaf blight symptoms were observed in all the inoculated leaves. The inoculated leaves showed severe browning near the inoculation site (1-2 cm), and advanced yellowing from 2 to 7 cm from the inoculation site, while no symptoms were found in control group. The pathogen was recovered from the infected leaves, and its identity was confirmed by 16S rRNA/gyrB sequencing and morphological analysis, fulfilling Koch's postulates (Fig 2). To our knowledge, this is the first report of E. asburiae causing bacterial leaf blight on sorghum worldwide. This species is a well-known pathogen of humans that can cause nosocomial infections (Markovska et al. 2019; Zhu et al. 2017). Recently, E. asburiae was identified as the causal agent of bacterial blight on rice and tuber rot on radish (Wang et al. 2023; Yu et al. 2021). The emergence E. asburiae as a plant pathogen may be produced by the numerous resistant strains reported during recent years. Pantoea ananatis has been reported as a common companion pathogen of E. asburiae (Xue et al. 2021). This report will help to better understand the host promiscuity of E. asburiae and reveals a new pathogen that affects sorghum production in China. This study also serves as a basis for future studies to develop management strategies and cultivation for the disease to prevent sorghum yield loss. As far as we know, no control method for the management of this new plant pathogen was reported to date, which highlights the potential hazard of this discovery. Reference Hoffmann, H., et al. 2005. Syst. Appl. Microbiol. 28:196. Kauffman, H. E., et al. 1973. Plant Dis. Rep. 57:537. Marchesi, J. R., et al. 1998. Appl. Environ. Microbiol. 64:795. Markovska, R., et al. 2019. Infect. Dis. 51:627. Wang, R., et al. 2023. Plant Dis. in press. https://doi.org/10.1094/PDIS-11-22-2650-PDN Xue, Y., et al. 2021. Plant Dis. 105:2078. Yamamoto, S., et al. 1995. Appl. Environ. Microbiol. 61:1104. Yu, L., et al. 2021. Plant Dis. 106:310. Zhu, B., et al. 2017. J. Glob. Antimicrob. Resist. 8:104.

Host-adaptive traits in the plant-colonizing Pseudomonas donghuensis P482 revealed by transcriptomic responses to exudates of tomato and maize

Pseudomonads are metabolically flexible and can thrive on different plant hosts. However, the metabolic adaptations required for host promiscuity are unknown. Here, we addressed this knowledge gap by employing RNAseq and comparing transcriptomic responses of Pseudomonas donghuensis P482 to root exudates of two plant hosts: tomato and maize. Our main goal was to identify the differences and the common points between these two responses. Pathways upregulated only by tomato exudates included nitric oxide detoxification, repair of iron-sulfur clusters, respiration through the cyanide-insensitive cytochrome bd, and catabolism of amino and/or fatty acids. The first two indicate the presence of NO donors in the exudates of the test plants. Maize specifically induced the activity of MexE RND-type efflux pump and copper tolerance. Genes associated with motility were induced by maize but repressed by tomato. The shared response to exudates seemed to be affected both by compounds originating from the plants and those from their growth environment: arsenic resistance and bacterioferritin synthesis were upregulated, while sulfur assimilation, sensing of ferric citrate and/or other iron carriers, heme acquisition, and transport of polar amino acids were downregulated. Our results provide directions to explore mechanisms of host adaptation in plant-associated microorganisms.

Regional microbiome differentiation of the invasive Sargassum muticum (Fucales, Phaeophyceae) follows the generalist host hypothesis across the North East Atlantic

ABSTRACT Over 90% of introduced marine species are seaweeds. Seaweeds rely on their microbiome for host settlement, nutrition, development and health. As such, it is likely that microbiomes are involved in seaweed invasions. Sargassum muticum, indigenous to Southeast Asia, inhabits the North-east Atlantic from Norway to Morocco. This is the only known successful case of a non-clonal marine invader with almost no genetic variation over its large NE Atlantic introduced range. This makes it a very interesting model to study an invasive seaweeds microbiome, as it practically uncouples host genetic variation from microbiome variation. Associated bacteria potentially contribute to the plasticity and acclimation of S. muticum leading to its success over the last 50 years. Dispersing host organisms can either bring their acquired microbes along or obtain new ones locally, following the mutualist and generalist host hypothesis, respectively. We used partial 16S rRNA gene amplicon sequencing to characterize the total and core microbiome across S. muticum structures/tissues from five NE Atlantic regions, from Norway to Morocco, covering over 30° of latitude. In contrast to host genotypes, highly diverse, regional, total and core microbiomes, with differentiation levels depending on tissue, bacterial community structure were detected. Atlantic S. muticum follows the generalist host hypothesis, possibly recruiting a new microbiome in each new region. This host promiscuity may promote the invasiveness of S. muticum. Diversity was lower in the young/annual tissues compared with the older tissues for the total bacterial community, suggesting that these are mostly transitory bacteria accumulating over time in the older parts. The total core microbiome included 10 OTUs, representing dominant community members commonly found in other seaweeds’ cores. The core Granulosicoccus OTU followed a clear regional pattern where northern and southern regions clustered differentially, suggesting a regional signature even at an OTU level. HIGHLIGHTS North-east (NE) Atlantic Sargassum muticum microbiome differentiation does not match host genetic background. NE Atlantic S. muticum shows a geographic region and tissue-specific total and core bacterial community matching bestthe generalist host hypothesis. Core OTU – the bacterium Granulosicoccus – shows a strong regional specialization.

First Report of Epicoccum sorghinum Causing Leaf Sheath and Leaf Spot on Maize in China.

In November 2020, leaf sheath on maize (Zea mays) was detected in southeastern Jiangsu (Nantong municipality; 120.54° E, 31.58° N) in China. Physiologically mature plants, 13 weeks of cultivation (at the harvest stage), exhibited red-brown lesions in stem and leaves, and dried-up stem (Figure 1). The symptoms were observed on approximately 95% of the maize plants in a 0.8 ha maize field surrounded by old sorghum fields and the crop yield was decreased by 70-85% with respect previous years, when no disease symptoms were detected. Small pieces, approximately 0.3 cm2 in size, of symptomatic tissue were surface sterilized in 1.5% NaOCl for 1 min, and washed twice with sterile ddH2O. The pathogen was isolated (one isolate was obtained) and cultured on PDA medium, containing chloramphenicol (50 µg/mL), under darkness at 26 ºC for 3 days. Amplification of internal transcribed spacer (ITS), large subunit (LSU), actin (ACT) and β-tubulin (TUB2) genes was performed using ITS1/ITS4, LR0R/LR7, ACT512F/ACT783R and T1/Bt2b primers, respectively (Ma et al. 2021). Sequences were submitted to GenBank under accession numbers MW800180 (ITS), MW800361 (LSU), MW845677 (ACT) and MW892439 (TUB2). Blast search revealed that the ITS sequence had 100% (492/492 bp) homology with E. sorghinum LY-D-1-1, MT604999, LSU had 98% (1075/1091 bp) homology with E. sorghinum GZDS2018BXT010, MK516207, ACT had 96% (214/222 bp) homology with E. sorghinum M3, MK044832, and TUB2 had 99% (498/499 bp) homology with E. sorghinum BJ-F1, MF987525. Molecular phylogenetic tree was constructed using MEGA7 to confirm the identity of the pathogen. The evolutionary history was inferred by using the Maximum Likelihood method based on the Tamura 3-parameter model, and the tree with the highest likelihood (-1774.9882) is shown in Figure 2. Bipolaris, Curvularia and Fusarium spp. found causing leaf spot on maize were included in the phylogenetic tree (Liu et al. 2021; Reyes Gaige et al. 2020; Chang et al. 2016). To confirm pathogenicity, a sterilized spatula was used to make wounds (3 mm diameter, 1 mm depth) on the stem and leaves of 2-week old maize plants. A solution containing 1 × 108 spores/mL (20 µL) was injected in the wound, whereas sterilized ddH2O was used in the control experiment. Inoculated plants were maintained in a growth chamber at 28 °C and 60% relative humidity for 3 days, observing fast-growing necrotic lesions in both stem and leaves. The pathogen was recovered from the infected plants and its identity was confirmed by morphological and sequence analyses. Microscope observations indicated the presence of chlamydospores, oval conidia (3 × 5 µm) and round pycnidia (60-100 µm diameter), and agree with those previously reported for the morphology of E. sorghinum (Bao et al. 2019). During last 2 years, E. sorghinum was reported to cause leaf spot on a number of relevant agricultural crops in China, including taro, Brassica parachinensis, tea, rice and wheat (Du et al. 2020; Li et al. 2020; Liu et al. 2020a, 2020b), confirming the expansion and host promiscuity of this pathogen. The pathogen was also reported to cause leaf spot on maize in Brazil in 2004 (Do Amaral et al. 2004); however, this is the first report of E. sorghinum causing leaf sheath and leaf spot on maize in China. Maize an important agricultural crop in China with more than 168 million tons produced in 2019. The observed yield loss and disease incidence of the isolated strain suggest that E. sorghinum may be a threat to maize production in China.

The role of host promiscuity in the invasion process of a seaweed holobiont

Invasive species are co-introduced with microbiota from their native range and also interact with microbiota found in the novel environment to which they are introduced. Host flexibility toward microbiota, or host promiscuity, is an important trait underlying terrestrial plant invasions. To test whether host promiscuity may be important in macroalgal invasions, we experimentally simulated an invasion in a common garden setting, using the widespread invasive macroalga Agarophyton vermiculophyllum as a model invasive seaweed holobiont. After disturbing the microbiota of individuals from native and non-native populations with antibiotics, we monitored the microbial succession trajectories in the presence of a new source of microbes. Microbial communities were strongly impacted by the treatment and changed compositionally and in terms of diversity but recovered functionally by the end of the experiment in most respects. Beta-diversity in disturbed holobionts strongly decreased, indicating that different populations configure more similar –or more common– microbial communities when exposed to the same conditions. This decline in beta-diversity occurred not only more rapidly, but was also more pronounced in non-native populations, while individuals from native populations retained communities more similar to those observed in the field. This study demonstrates that microbial communities of non-native A. vermiculophyllum are more flexibly adjusted to the environment and suggests that an intraspecific increase in host promiscuity has promoted the invasion process of A. vermiculophyllum. This phenomenon may be important among invasive macroalgal holobionts in general.

First Report of Botryosphaeria dothidea Causing Stem Canker on Soybean in China.

In September 2020, widespread stem canker on soybean (Glycine max) was detected in southeastern Jiangsu (Nantong municipality; 120.76° E, 32.23° N) in China. Mature plants, 14 weeks of cultivation, exhibited brown necrotic lesions and dried-up stem. The symptoms were observed in eleven soybean fields, 1.6 ha in total, and approximately 80% of the plants were symptomatic. The symptoms were consistent with those previously reported for stem canker on soybean caused by Diaporthe aspalathi, D. caulivora and D. sojae (Ghimire et al. 2019; Mena et al. 2020). Small pieces, approximately 0.4 cm2 in size, of symptomatic tissue were surface sterilized in 1.5% NaOCl for 1 min, and washed twice with sterile ddH2O. The pathogen was isolated and cultured on potato dextrose agar (PDA), containing chloramphenicol (50 µg/mL), under darkness at 28 ºC for 7 days. Amplification of internal transcribed spacer (ITS), elongation factor 1-α (EF1-α) and β-tubulin (TUB2) genes was performed using ITS1/ITS4, EF1-728F/EF1-986R and Bt2a/Bt2b primers, respectively (Jia et al. 2019). Sequences were submitted to GenBank under accession numbers MW130133 (ITS), MW147481 (EF1-α) and MW147482 (TUB2). Blast search revealed that the amplified sequences had 99.65% (ITS; B. dothidea JZB310202, MN945381), 100% (EF1-α; B. dothidea ZB-77, MH726166) and 99.75% (TUB2; B. dothidea ZB-1, MN642587) matches to multiple B. dothidea strains, whereas all reported Diaporthe strains showed no nucleotide identity to the amplified sequences. Molecular phylogenetic tree was constructed using MEGA7 to confirm the identity of the pathogen. ITS, EF1-α and TUB2 sequences were blasted separately in Muscle (https://www.ebi.ac.uk/Tools/msa/muscle/) and then combined together to make the phylogenetic tree. The evolutionary history was inferred by using the Maximum Likelihood method based on the Tamura 3-parameter model, and the tree with the highest likelihood (-4291.3981) is shown in Figure 1. Diaporthe strains found causing stem canker on soybean, some Phytophthora sojae strains (which also cause dried-up stem on soybean) (Yang et al. 2019), and B. dothidea strains found in China in other hosts were included in the phylogenetic tree. To confirm pathogenicity, a sterilized spatula was used to make wounds (3 mm diameter, 1 mm depth) on the stem of 2-week old soybean plants. Mycelial plugs from a 7 day-old culture on PDA were placed on the wounds and covered with Parafilm. Sterilized PDA plugs were used as control. Inoculated plants were maintained in a growth chamber at 28 °C and 60% relative humidity. Typical stem canker symptoms were observed 5 days after inoculation (Figure 2). Microscope observations showed the presence of septate mycelium, fusiform conidia and round conidiomata, and agreed with those previously reported for the morphology of B. dothidea strains (Phillips et al. 2013). During recent months, B. dothidea was reported to cause stem canker and leave wilt on a number of plant species in China (Huang et al. 2020; Ju et al. 2020; Wang et al. 2020a, 2020b, 2020c), confirming the expansion and host promiscuity of this pathogen. Stem canker on soybean has been thoroughly associated to Diaporthe strains; however, this is the first report of B. dothidea causing this disease. We believe that our results will help to better understand the pathogens affecting soybean production in China.

Erratum: Patchy promiscuity: machine learning applied to predict the host specificity of Salmonella enterica and Escherichia coli.

Salmonella enterica and Escherichia coli are bacterial species that colonize different animal hosts with sub-types that can cause life-threatening infections in humans. Source attribution of zoonoses is an important goal for infection control as is identification of isolates in reservoir hosts that represent a threat to human health. In this study, host specificity and zoonotic potential were predicted using machine learning in which Support Vector Machine (SVM) classifiers were built based on predicted proteins from whole genome sequences. Analysis of over 1000 S. enterica genomes allowed the correct prediction (67 –90 % accuracy) of the source host for S. Typhimurium isolates and the same classifier could then differentiate the source host for alternative serovars such as S. Dublin. A key finding from both phylogeny and SVM methods was that the majority of isolates were assigned to host-specific sub-clusters and had high host-specific SVM scores. Moreover, only a minor subset of isolates had high probability scores for multiple hosts, indicating generalists with genetic content that may facilitate transition between hosts. The same approach correctly identified human versus bovine E. coli isolates (83 % accuracy) and the potential of the classifier to predict a zoonotic threat was demonstrated using E. coli O157. This research indicates marked host restriction for both S. enterica and E. coli, with only limited isolate subsets exhibiting host promiscuity by gene content. Machine learning can be successfully applied to interrogate source attribution of bacterial isolates and has the capacity to predict zoonotic potential.

Patchy promiscuity: machine learning applied to predict the host specificity of Salmonella enterica and Escherichia coli.

Salmonella enterica and Escherichia coli are bacterial species that colonize different animal hosts with sub-types that can cause life-threatening infections in humans. Source attribution of zoonoses is an important goal for infection control as is identification of isolates in reservoir hosts that represent a threat to human health. In this study, host specificity and zoonotic potential were predicted using machine learning in which Support Vector Machine (SVM) classifiers were built based on predicted proteins from whole genome sequences. Analysis of over 1000 S. enterica genomes allowed the correct prediction (67 –90 % accuracy) of the source host for S. Typhimurium isolates and the same classifier could then differentiate the source host for alternative serovars such as S. Dublin. A key finding from both phylogeny and SVM methods was that the majority of isolates were assigned to host-specific sub-clusters and had high host-specific SVM scores. Moreover, only a minor subset of isolates had high probability scores for multiple hosts, indicating generalists with genetic content that may facilitate transition between hosts. The same approach correctly identified human versus bovine E. coli isolates (83 % accuracy) and the potential of the classifier to predict a zoonotic threat was demonstrated using E. coli O157. This research indicates marked host restriction for both S. enterica and E. coli, with only limited isolate subsets exhibiting host promiscuity by gene content. Machine learning can be successfully applied to interrogate source attribution of bacterial isolates and has the capacity to predict zoonotic potential.

Differential plant invasiveness is not always driven by host promiscuity with bacterial symbionts.

Identification of mechanisms that allow some species to outcompete others is a fundamental goal in ecology and invasive species management. One useful approach is to examine congeners varying in invasiveness in a comparative framework across native and invaded ranges. Acacia species have been widely introduced outside their native range of Australia, and a subset of these species have become invasive in multiple parts of the world. Within specific regions, the invasive status of these species varies. Our study examined whether a key mechanism in the life history of Acacia species, the legume-rhizobia symbiosis, influences acacia invasiveness on a regional scale. To assess the extent to which species varying in invasiveness correspondingly differ with regard to the diversity of rhizobia they associate with, we grew seven Acacia species ranging in invasiveness in California in multiple soils from both their native (Australia) and introduced (California) ranges. In particular, the aim was to determine whether more invasive species formed symbioses with a wider diversity of rhizobial strains (i.e. are more promiscuous hosts). We measured and compared plant performance, including aboveground biomass, survival, and nodulation response, as well as rhizobial community composition and richness. Host promiscuity did not differ among invasiveness categories. Acacia species that varied in invasiveness differed in aboveground biomass for only one soil and did not differ in survival or nodulation within individual soils. In addition, acacias did not differ in rhizobial richness among invasiveness categories. However, nodulation differed between regions and was generally higher in the native than introduced range. Our results suggest that all Acacia species introduced to California are promiscuous hosts and that host promiscuity per se does not explain the observed differences in invasiveness within this region. Our study also highlights the utility of assessing potential mechanisms of invasion in species' native and introduced ranges.

Host promiscuity in symbiont associations can influence exotic legume establishment and colonization of novel ranges

Aim Invasive Acacia species have negatively impacted natural areas in multiple regions around the globe. Almost 400 Acacia species have been introduced outside their native ranges in Australia; approximately 6% have become invasive, 12% are naturalized, and 82% have no record of naturalization or invasion. This variation in invasiveness provides a comparative framework in which to examine mechanisms that either promote or constrain establishment and colonization of species in novel regions. Here, we experimentally examine the role that the legume–rhizobia symbiosis plays in the differential invasiveness of acacias introduced outside their native Australian ranges. Location Canberra, Australia. Methods We paired 12 Acacia species ranging in invasiveness globally with 12 rhizobial strains ranging in average symbiotic effectiveness. We measured plant growth and nodulation success and abundance to assess whether invasive acacias were more promiscuous hosts, that is had positive growth and nodulation responses to a broader range of rhizobial strains than naturalized and non-invasive species. Results Invasive acacias had a higher growth response across more rhizobial strains (six of 12 strains) than naturalized and non-invasive species, but invasiveness categories differed only moderately with regard to the percentage of plants with nodules and nodulation abundance. Main conclusion With respect to plant growth, invasive acacias appear to be more promiscuous hosts than naturalized and non-invasive Australian Acacia species. Plant growth response to nodulation, however, is likely more important than nodulation alone in the successful invasion of species in novel ranges. Results from this study help elucidate an important mechanism in the invasive capacity of legumes.

Varicella Zoster Virus and the Neuro-Attenuated Vaccine Necessity

Varicella Zoster Virus and the Neuro-Attenuated Vaccine Necessity

A video clip of the biting midge Culicoides anophelis ingesting blood from an engorged Anopheles mosquito in Hainan, China

BackgroundBiting midges are hematophagus ectoparasites of insects, humans and other animals. Culicoides (Trithicoides) anophelis Edwards1922 is a predator of engorged mosquitoes.FindingsIn a field trip of wild mosquito collections, C. anophelis was found on two Anopheles mosquitoes. One mosquito with a midge clinging onto its abdomen was caught on video demonstrating the act of the midge taking blood from the engorged mosquito Anopheles vagus. The midge C. anophelis has a broad host range. Documented in the literature, the midge has been found in various mosquito species in the genera Anopheles, Culex, Aedes and Armigeres.ConclusionsA video clip was presented demonstrating a midge taking blood from an engorged mosquito. The host promiscuity of C. anophelis raises a concern about its potential as a mechanic or biological vector to spread viruses among mosquito populations.

A parasitic selfish gene that affects host promiscuity

Selfish genes demonstrate transmission bias and invade sexual populations despite conferring no benefit to their hosts. While the molecular genetics and evolutionary dynamics of selfish genes are reasonably well characterized, their effects on hosts are not. Homing endonuclease genes (HEGs) are one well-studied family of selfish genes that are assumed to be benign. However, we show that carrying HEGs is costly for Saccharomyces cerevisiae, demonstrating that these genetic elements are not necessarily benign but maybe parasitic. We estimate a selective load of approximately 1-2% in 'natural' niches. The second aspect we examine is the ability of HEGs to affect hosts' sexual behaviour. As all selfish genes critically rely on sex for spread, then any selfish gene correlated with increased host sexuality will enjoy a transmission advantage. While classic parasites are known to manipulate host behaviour, we are not aware of any evidence showing a selfish gene is capable of affecting host promiscuity. The data presented here show a selfish element may increase the propensity of its eukaryote host to undergo sex and along with increased rates of non-Mendelian inheritance, this may counterbalance mitotic selective load and promote spread. Demonstration that selfish genes are correlated with increased promiscuity in eukaryotes connects with ideas suggesting that selfish genes promoted the evolution of sex initially.

89. Isolation of a Close AAV5 Relative from Goat Tissues: Evidence of Host Promiscuity

Top of pageAbstract Preexisting immunity to AAV vectors can potentially limit their clinical usefulness by blocking tissue transduction and/or by causing the elimination of vector-transduced cells. We previously demonstrated that the AAV2-neutralizing capacities of human plasmas (as measured by in vitro assay) are frequently substantial relative to proposed doses of AAV vectors. Out of a group of 50 hemophiliacs, approximately 40% had AAV2-neutralizing capacities exceeding 1e13 viral particles/ml or about 6e16 viral particles/total blood volume. Furthermore, the majority of the group with high anti-AAV2 titers also had significant titers against other AAV serotypes (AAV1, and 3–6). To create improved gene therapy vectors, we are currently screening tissues and adenovirus preparations from a wide variety of non-primate species to isolate AAV capsids that have less preexisting immunity in humans. One of the more surprising results from this screen was the PCR amplification of a close AAV5 relative from a crude goat adenovirus preparation. AAV5 is a human parvovirus, originally isolated from a penile flat condylomatous lesion, with a high sero-prevalence in the post-pubertal population. The goat adenovirus preparation used as the PCR template was produced during routine diagnostic adenovirus screening of a tissue sample from a goat that had died of enteritis. The presence of parvovirus-like particles in the initial stock was demonstrated by electron microscopy and no primate-derived products were used at any point in the viral culture. The 2,805 bp goat AAV PCR fragment, which encodes 603 bp of rep, the central intron, and all of cap, is 94 % homologous to AAV5. The DNA and protein homologies to AAV5 for the partial rep region are 98% and 99%, respectively, and are 93% and 94% for the cap region, respectively. With respect to the linear amino acid sequence, the distribution of the amino acid differences between the AAV5 and goat AAV capsids is highly polar. All of the 44 amino acid differences occur exclusively in the C-terminal hypervariable region of the capsid protein in a scattered fashion. It has been proposed that this region comprises the surface loops of AAV5 by analogy to AAV2. Because of its high homology to AAV5, it is likely that the goat AAV arose from a recent species jump of AAV5 from humans to goats. The fact that all of the amino acid differences between the AAV5 and the goat capsids occur in regions that are probably surface exposed implies that capsid evolution is being driven primarily by the humoral immune system of the new host or by adaptation to ruminant receptors. The lack of amino acid changes in non-surface exposed regions of cap may imply a lack of pressure from the cellular immune response. Interspecies infection, particularly in the case of domestic animals, may be a previously unappreciated but significant mechanism for diversity generation and virus evolution for AAVs. This novel goat AAV capsid has been successfully used to pseudo-type AAV2 vector genomes and is currently being evaluated for tissue tropism and resistance to human preexisting humoral immunity.

Selfish DNA and breeding system in flowering plants

In many species, some individuals carry one or more B chromosomes: extra, or supernumerary chromosomes not part of the normal complement. In most well–studied cases, Bs lower the fitness of their carrier and persist in populations only because of accumulation mechanisms analogous to meiotic drive. It has been suggested that such genomic parasites are expected to persist only in outcrossed sexual species, in which uninfected lines of descent can be continuously reinfected; in inbred or asexual species, all selection is between lines of descent, and the genomic parasites are either lost or must evolve into commensals or mutualists. Here we present a simple population genetic model of the effect of outcrossing rate on the frequency of B chromosomes, and find that outcrossing facilitates the spread of parasitic Bs, but inhibits the spread of mutualists. Data compiled from the literature on breeding system and B chromosomes of British plants indicate that Bs are much more likely to be reported from obligately outcrossed species than inbred species. These results support the ideas that most B chromosomes are parasitic, and that breeding systems play a central role in the biology of selfish genes.

Molecular phylogeny of the actinorhizal Hamamelidae and relationships with host promiscuity towards Frankia

AbstractSeveral of the most studied actinorhizal symbioses involve associations between host plants in the subclass Hamamelidae of the dicots and actinomycetes of the genus Frankia. These actinorhizal plants comprise eight genera distributed among three families of ‘higher’ Hamamelidae, the Betulaceae, Myricaceae, and Casuarinaceae. Contrasting promiscuity towards Frankia is encountered among the different actinorhizal members of these families, and a better assessment of the evolutionary history of these actinorhizal taxa could help to understand the observed contrasts and their implications for the ecology and evolution of the actinorhizal symbiosis. Complete DNA sequences of the chloroplast gene coding for the large subunit of ribulose 1,5‐bisphosphate carboxylase (rbcL) were obtained from taxa representative of these families and the Fagaceae. The phylogenetic relationships among and within these families were estimated using parsimony and distance‐matrix approaches. All families appeared monophyletic. The Myricaceae appeared to derive first before the Betulaceae and the Casuarinaceae. In the Casuarinaceae, the genus Gymnostoma derived before the genera Casuarina and Allocasuarina, which were found closely related. The analysis of character‐state changes in promiscuity along the consensus tree topology suggested a strong relationship between the evolutionary history of host plants and their promiscuity toward Frankia. Indeed, the actinorhizal taxa that diverged more recently in this group of plants were shown to be susceptible to a narrower spectrum of Frankia strains. The results also suggest that the ancestor of this group of plant was highly promiscuous, and that evolution has proceeded toward narrower promiscuity and greater specialization. These results imply that a tight relationship between the phytogenies of both symbiotic partners should not be expected, and that host promiscuity is likely to be a key determinant in the establishment of an effective symbiosis.