Cane toads, an invasive species in Australia, are resistant to fungal pathogens affecting frogs worldwide (Batrachochytrium dendrobatidis). From toad skin swabs, we detected higher proportions of ...bacteria with antifungal properties in Queensland, where toad and pathogen distributions overlap, than in other sites. This finding suggests that site-specific pathogen pressures help shape skin microbial communities.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Free-living hosts encounter pathogens at a wide range of frequencies and concentrations, including low doses that are largely aclinical, creating a varied landscape of exposure history and ...reinfection likelihood. While several studies show that higher priming doses result in stronger immunological protection against reinfection, it remains unknown how the reinfection challenge dose and priming dose interact to determine the likelihood and severity of reinfection. We manipulated both priming and challenge doses of Mycoplasma gallisepticum, which causes mycoplasmal conjunctivitis, in captive house finches (Haemorhous mexicanus), to assess reinfection probability and severity. We found a significant interaction between priming and challenge doses on reinfection probability, with the likelihood of reinfection by a high but not a low challenge dose decreasing exponentially at higher priming doses. While this interaction was likely driven by lower average infection probabilities for low-dose versus high-dose challenges, even the highest priming dose provided only negligible protection against reinfection from low-dose challenges. Similarly, pathogen loads during reinfection were significantly reduced with increasing priming doses only for birds reinfected at high but not low doses. We hypothesize that these interactions arise to some degree from fundamental differences in host immune responses across doses, with single low doses only weakly triggering host immune responses. Importantly, our results also demonstrate that reinfections can occur from a variety of exposure doses and across diverse degrees of standing immunity in this system. Overall, our study highlights the importance of considering both initial and subsequent exposure doses where repeated exposure to a pathogen is common in nature.
Mycoplasma agassizii is a common cause of upper respiratory tract disease in Mojave desert tortoises (Gopherus agassizii). So far, only two strains of this bacterium have been sequenced, and very ...little is known about its patterns of genetic diversity. Understanding genetic variability of this pathogen is essential to implement conservation programs for their threatened, long-lived hosts. We used next generation sequencing to explore the genomic diversity of 86 cultured samples of M. agassizii collected from mostly healthy Mojave and Sonoran desert tortoises in 2011 and 2012. All samples with enough sequencing coverage exhibited a higher similarity to M. agassizii strain PS6T (collected in Las Vegas Valley, Nevada) than to strain 723 (collected in Sanibel Island, Florida). All eight genomes with a sequencing coverage over 2x were subjected to multiple analyses to detect single-nucleotide polymorphisms (SNPs). Strikingly, even though we detected 1373 SNPs between strains PS6T and 723, we did not detect any SNP between PS6T and our eight samples. Our whole genome analyses reveal that M. agassizii strain PS6T may be present across a wide geographic extent in healthy Mojave and Sonoran desert tortoises.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract Considerable research has focused on microbes on amphibian skin, as they act as the first line of defense against invading pathogens. This effort has generated substantial data on patterns ...across species, space, time, and ontogeny, alongside a growing list of beneficial antifungal symbionts. Though there is evidence of stability in amphibian skin microbial communities, there is also an indication that regular skin shedding reduces cultivable bacteria, with regrowth and recolonization in the period between sheds. This suggests that skin communities are in constant flux, and we lack an understanding of how the membership and structure of those communities are affected by shedding events. In this study, we conducted experiments on cane toads ( Rhinella marina ) to investigate the influence of shedding on skin microbiomes. We first used quantitative PCR to verify a positive correlation between bacterial loads and time in the days after shedding. We then resampled individuals over time to describe changes in community composition in the 38 h after shedding using amplicon sequencing. Similar to trends of bacterial loads, we found increases in alpha diversity over time after shedding, suggesting that shedding reduces bacterial diversity as it knocks down bacterial loads. During the 38‐h period, community structure became similar to pre‐shed communities in some individuals, but there was no consistent pattern in structural changes among individuals. In light of the amphibian chytridiomycosis pandemic, understanding how physiological events such as skin shedding affect beneficial bacteria and communities on amphibians would provide important insight into amphibian ecology.
ABSTRACT
The commensal microbes inhabiting a host tissue can interact with invading pathogens and host physiology in ways that alter pathogen growth and disease manifestation. Prior work in house ...finches (Haemorhous mexicanus) found that resident ocular microbiomes were protective against conjunctival infection and disease caused by a relatively high dose of Mycoplasma gallisepticum. Here, we used wild-caught house finches to experimentally examine whether protective effects of the resident ocular microbiome vary with the dose of invading pathogen. We hypothesized that commensal protection would be strongest at low M. gallisepticum inoculation doses because the resident microbiome would be less disrupted by invading pathogen. Our five M. gallisepticum dose treatments were fully factorial with an antibiotic treatment to perturb resident microbes just prior to M. gallisepticum inoculation. Unexpectedly, we found no indication of protective effects of the resident microbiome at any pathogen inoculation dose, which was inconsistent with the prior work. The ocular bacterial communities at the beginning of our experiment differed significantly from those previously reported in local wild-caught house finches, likely causing this discrepancy. These variable results underscore that microbiome-based protection in natural systems can be context dependent, and natural variation in community composition may alter the function of resident microbiomes in free-living animals.
Bacterial communities can be key in protecting hosts against pathogens, but that protection depends on which bacteria make up resident communities during pathogen invasion. Photo credit: Sara Teemer
Migratory animals can carry symbionts over long distances. While well-studied for parasite and pathogen transmission, less is known about use of this route by other symbiotic taxa, particularly those ...non-pathogenic. Here we ask the question of whether gut bacteria can be spread between continents by long-distance bird migration, although gut microbiomes in birds may not be as stable or persistent as those of non-volant animals. We used amplicon sequencing of both bacterial 16S rRNA gene and
Vibrio
-centric hsp60 gene to determine whether the faecal bacteria of migratory great knots (
Calidris tenuirostris
) also occur in their main food source in Northern Australia or in nearby sand, comparing samples before and after the birds’ long-distance migration. Our data suggest that there is little connectivity among the bacterial microbiomes, except in the bivalve prey. Our results are consistent with previous studies finding that bird faecal microbiomes were not host-specific and contrast with those showing an influence of diet on bird faecal bacteria. We also found little connectivity among
Vibrio
spp. However, although faecal sample sizes were small, the dominance of different individual
Vibrio
spp. suggests that they may have been well-established in knot guts and thus capable of moving with them on migration. We suggest that the physiological impacts of a long-distance migration may have caused shifts in the phyla comprising great knot faecal communities.
DNA‐based methods to measure the abundance and relative abundance of bacterial taxa can be skewed by the presence of dead or transient bacteria. Consequently, the active, functional members of the ...community may be a small subset of the detected bacterial community. This mismatch can make inferences about the roles of communities in host health difficult and can be particularly problematic for low‐abundance microbiomes, such as those on conjunctival surfaces. In this study, we manipulated bacterial communities on bird conjunctiva with a bacteriostatic antibiotic, reducing bacterial activity while preserving viability, to identify the living and active conjunctival communities using comparisons of 16S ribosomal DNA and RNA in paired samples. DNA amplicons included many more sequence variants than RNA amplicons from the same communities, with consequent differences in diversity. While we found that changes in communities in DNA samples broadly represent shifts in the living (RNA‐amplicon) communities, assessments of community function may be better described by RNA samples, reducing background noise from dead cells. We further used these data to test RNA:DNA ratios, used in other microbiological contexts, to detect shifts in bacterial activity after antibiotic disruption but were unable to detect changes in bacterial activity with this method.
Sequencing DNA versus RNA samples can overestimate bacterial community members from the eye of a small songbird but still provide an adequate representation of bacterial communities and changes therein. Photo credit: Sara R. Teemer.
Animal skin acts as a barrier between the organism and its environment and provides the first line of defense against invading pathogens. Thus, skin surfaces harbor communities of microbes that are ...interacting with both the host and its environment. Amphibian skin bacteria form distinct communities closely tied to their host species, but few studies have compared bacterial communities between amphibians and other, non-amphibian sympatric animals. Notably, skin microbes on reptiles have gained little attention. We used next-generation sequencing technology to describe bacterial communities on the skin of three lizard species and compared them to bacteria on six cohabiting frog species in the Northern Territory of Australia. We found bacterial communities had higher richness and diversity on lizards than frogs, with different community composition between reptiles and amphibians and among species. Core bacteria on the three lizard species overlapped by over 100 operational taxonomic units. The bacterial communities were similar within species of frogs and lizards, but the communities tended to be more similar between lizard species than between frog species and when comparing lizards with frogs. The diverse bacteria found on lizards invites further questions on how and how well reptiles interact with microorganisms through their scaly skin.
Infections can have far-reaching sublethal effects on wildlife, including reduced maintenance of external structures. For many wildlife taxa, daily maintenance of external structures (termed preening ...in birds) is critical to fitness, but few studies have examined how infections alter such maintenance. Mycoplasma gallisepticum is a common pathogen in free-living House Finches (Haemorhous mexicanus), where it causes mycoplasmal conjunctivitis. Despite documented behavioral changes associated with M. gallisepticum infections in finches, no studies have examined how preening behavior may change with infection and how potential differences in preening may affect feather quality. To test this, we experimentally inoculated captive House Finches with M. gallisepticum or a control treatment, and we collected behavioral and feather quality data to detect potential changes in feather maintenance due to infection. We found that finches infected with M. gallisepticum preened significantly less often, and within the infected treatment, birds with the highest conjunctivitis severity preened the least often. However, there was no difference in the quality scores for secondary flight feathers collected from control versus infected birds. We also assayed feather water retention and found that the degree of water retention correlated with our feather quality scores, such that feathers with poor scores retained more water. However, as with quality scores, feather water retention did not differ with infection; this may be due to the controlled environment that the birds experienced while in captivity. Our data suggest that, in addition to sickness behaviors previously observed in finches, M. gallisepticum infection decreases other behaviors critical to survival, such as preening. While the consequences of reduced preening on feather maintenance were not apparent in captive conditions, further work is needed to determine whether House Finches in the wild that are infected with M. gallisepticum experience a fitness cost, such as increases in ectoparasite loads, due to this reduced feather maintenance.
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