Potential impacts of environmental bacteria on the microbiota of loggerhead (Caretta caretta) and green (Chelonia mydas) sea turtle eggs and their hatching success

Sea turtle hatching success can be affected by many variables, including pathogenic microbes, but it is unclear which microbes are most impactful and how they are transmitted into the eggs. This study characterized and compared the bacterial communities from the (i) cloaca of nesting sea turtles (ii) sand within and surrounding the nests; and (iii) hatched and unhatched eggshells from loggerhead (Caretta caretta) and green (Chelonia mydas) turtles. High throughput sequencing of bacterial 16S ribosomal RNA gene V4 region amplicons was performed on samples collected from 27 total nests in Fort Lauderdale and Hillsboro beaches in southeast Florida, United States. Significant differences were identified between hatched and unhatched egg microbiota with the differences caused predominately by Pseudomonas spp., found in higher abundances in unhatched eggs (19.29% relative abundance) than hatched eggs (1.10% relative abundance). Microbiota similarities indicate that the nest sand environment, particularly nest distance from dunes, played a larger role than the nesting mother's cloaca in influencing hatched and unhatched egg microbiota. Pathogenic bacteria potentially derive from mixed-mode transmission or additional sources not included in this study as suggested by the high proportion (24%-48%) of unhatched egg microbiota derived from unknown sources. Nonetheless, the results suggest Pseudomonas as a candidate pathogen or opportunistic colonizer associated with sea turtle egg-hatching failure.

Mycotic Diseases in Chelonians

Turtles and 'tortoises' populations are declining in number, the factors driving extinction risks being related to habitat loss and degradation, climate change, introduction of invasive plant and animal species, consumption by humans for food and medicinal use, and collection for international pet trade. Fungal infections represent one of the main threats for ecosystem health. The present narrative review deals with conventional and emerging mycoses of Chelonians. Although conventional mycoses in captive and pet reptiles would depend on poor husbandry, being the agents mostly opportunistic pathogens, some fungal species were reported to occur more frequently, such as the entomopathogen Purpureocillium lilacinum. Furthermore, emerging agents such as the Fusarium solani species complex have been recognized as a real threat for the surviving of some aquatic species, acting as primary pathogens. This complex has been recently included within pathogens in One Health issues. Emydomyces testavorans is recognized as an emerging threat, although, due its recent identification, information about its epidemiology is limited. Data about treatments and outcomes of mycoses in Chelonians are also referred.

Environmental and pathological factors affecting the hatching success of the two northernmost loggerhead sea turtle (Caretta caretta) nests

In recent years, the report of loggerhead sea turtle (Caretta caretta) Mediterranean nesting range has expanded together with new records of nests becoming northward on the Italian coastline of the Tyrrhenian and Adriatic seas. These areas are characterized by intensive human activities, such as tourism, fishery, and marine traffic, all possibly involved in the influence of the use of coastal habitat by marine species. These anthropic threats, in addition to the natural ones and the changing environmental characteristics of the beach, may influence the growth of microorganisms causing hatching failures. Among microorganisms, fungal infection by the genus Fusarium (Link, 1809) is considered one of the main causes of globally declining sea turtle populations. In summer 2021, the two northernmost worldwide loggerhead sea turtle nests were monitored along the Northern Adriatic coastline (Veneto, Italy). These first records may potentially candidate this area as suitable for a large part of the loggerhead turtle's life cycle and it could represent a minor sea turtle nesting area that, according to Prato and colleagues, remained unnoticed due to the lack of specific monitoring. Sea Turtle Egg Fusariosis (STEF) was deemed to have deeply compromised the hatching success of the northmost one. Climate change and anthropogenic impacts have been scored as one of the highest hazards to sea turtle health and could have played a role in the STEF development. Environmental changes, human activities, and emerging pathogens deserve the highest attention in terms of health research, and conservation management.

Species Diversity in the Fusarium solani (Neocosmospora) Complex and Their Pathogenicity for Plants and Humans

The Fusarium solani species complex is a large group of soil saprotrophs with a broad adaptive potential, which allows the fungi to exist under various conditions and to parasitize on different hosts. The review analyzes the modern data concerning the genetic peculiarities of species from this complex by the example of F. solani f. sp. pisi and generalizes the data on the most widespread species pathogenic for both plants and humans. The enhanced resistance of the F. solani species complex to the most of modern antifungal agents and the need for novel therapeutic agents against fusariosis has been considered.

Surface microbiota of Mediterranean loggerhead sea turtles unraveled by 16S and 18S amplicon sequencing

The loggerhead sea turtle is considered a keystone species with a major ecological role in Mediterranean marine environment. As is the case with other wild reptiles, their outer microbiome is rarely studied. Although there are several studies on sea turtle’s macro-epibionts and endo-microbiota, there has been little research on epibiotic microbiota associated with turtle skin and carapace. Therefore we aimed to provide the identification of combined epibiotic eukaryotic, bacterial and archaeal microbiota on Mediterranean loggerhead sea turtles. In this study, we sampled skins and carapaces of 26 loggerheads from the Mediterranean Sea during 2018 and 2019. To investigate the overall microbial diversity and composition, amplicon sequencing of 16S and 18S rRNA genes was performed. We found that the Mediterranean loggerhead sea turtle epibiotic microbiota is a reservoir of a vast variety of microbial species. Microbial communities mostly varied by different locations and seas, while within bacterial communities’ significant difference was observed between sampled body sites (carapace vs. skin). In terms of relative abundance, Proteobacteria and Bacteroidota were the most represented phyla within prokaryotes, while Alveolata and Stramenopiles thrived among eukaryotes. This study, besides providing a first survey of microbial eukaryotes on loggerheads via metabarcoding, identifies fine differences within both bacterial and eukaryotic microbial communities that seem to reflect the host anatomy and habitat. Multi-domain epi-microbiome surveys provide additional layers of information that are complementary with previous morphological studies and enable better understanding of the biology and ecology of these vulnerable marine reptiles.

Transcending sea turtles: first report of hatching failure in eggs of an Amazonian freshwater turtle with symptoms of the fungal emerging disease fusariosis

During the last few decades, fungal pathogens have caused devastating population declines across a broad range of taxa. A newly emerging fungal disease, sea turtle egg fusariosis, caused by members of the Fusarium solani species complex (FSSC), has been reported to be responsible for hatching failure in sea turtles worldwide. However, this has not been detected in fresh water turtle species. Here, using relocated clutches and artificial incubation, we report high hatching failure in eggs symptomatic of fusariosis in the yellow-spotted Amazon River turtle (Podocnemis unifilis) inhabiting a pristine environment in the Ecuadorian Amazon. In 2020, we screened 680 eggs of the yellow-spotted Amazon River turtle, relocated from wild nesting areas to artificial nests, for visual symptoms of fusariosis and to estimate hatchability despite infection. We selected 68 eggs sampled in 2019 to confirm Fusarium infection by PCR amplification of the TEF-1α gene and sequenced seven of those amplicons on an Illumina Miseq to assess FSSC membership. We observed fusariosis symptoms in 42% of the 680 eggs. The proportion of symptomatic eggs within nests was negatively linked to the proportion of eggs that hatched. Hatchability was 8% for symptomatic eggs compared with 72% of asymptomatic eggs. Through PCR testing, 58% of symptomatic and 8% of asymptomatic eggs sampled in 2019 tested positive for Fusarium spp., and sequencing revealed that nine sequence variants from three asymptomatic and four symptomatic eggs corresponded to F. keratoplasticum, F. solani, and F. falciforme, the three major FSSC pathogens reported in sea turtle egg fusariosis. Our study suggests that hatching failure in eggs linked to symptoms of fusariosis appears to be partially caused by Fusarium pathogens within FSSC in a freshwater turtle. Thus, fusariosis is more widespread among the Testudines than previously reported and is not limited to sea environments, findings of particular conservation concern. This article is protected by copyright. All rights reserved.

Fusarium species isolated from post-hatchling loggerhead sea turtles (Caretta caretta) in South Africa

Species in the Fusarium solani species complex are fast growing, environmental saprophytic fungi. Members of this genus are filamentous fungi with a wide geographical distribution. Fusarium keratoplasticum and F. falciforme have previously been isolated from sea turtle nests and have been associated with high egg mortality rates. Skin lesions were observed in a number of stranded, post-hatchling loggerhead sea turtles (Caretta caretta) in a rehabilitation facility in South Africa. Fungal hyphae were observed in epidermal scrapes of affected turtles and were isolated. The aim of this study was to characterise the Fusarium species that were isolated from these post-hatchling loggerhead sea turtles (Caretta caretta) that washed up on beaches along the South African coastline. Three gene regions were amplified and sequenced, namely the internal transcribed spacer region (ITS), a part of the nuclear large subunit (LSU), and part of the translation elongation factor 1 α (tef1) gene region. Molecular characteristics of strains isolated during this study showed high similarity with Fusarium isolates, which have previously been associated with high egg mortality rates in loggerhead sea turtles. This is the first record of F. keratoplasticum, F. falciforme and F. crassum isolated from stranded post-hatchling loggerhead sea turtles in South Africa.

Beyond Sea Turtles: Fusarium keratoplasticum in Eggshells of Podocnemis unifilis, a Threatened Amazonian Freshwater Turtle

The endangered yellow-spotted river turtle (Podocnemis unifilis) has experienced a dramatic population decline in the Ecuadorian Amazonia, mainly due to overexploitation of its eggs. To reverse this trend, the Wildlife Conservation Society has developed a head-start program in Yasuní National Park since 2008, but the potential risk that microbes associated with its eggs might represent for hatching success has not been evaluated yet. Members of the Fusarium solani species complex (FSSC) are involved in egg failure in sea turtles under natural and hatchery conditions, but their role in infecting the eggs of P. unifilis is unknown. In this study, we collected eggshells of P. unifilis and obtained 50 fungal and bacterial isolates. Some potentially pathogenic fungi of the genera Fusarium, Penicillium and Rhizopus were identified based on molecular data. Most importantly, the sea turtle pathogenic species F. keratoplasticum not only was present, but it was the most frequently found. Conversely, we have also isolated other microorganisms, such as Pseudomonas or Phoma-like species, producing a wide spectrum of antifungal compounds that may have a protective role against fungal diseases. Our survey provides useful information on potential pathogens found in P. unifilis eggshells, upon which the success of conservation programs may depend.

Development of species-specific primers for rapid identification by PCR of the ecologically important pathogen Fusarium keratoplasticum from isolated and environmental samples

The genus Fusarium contains many fungal species known to be pathogenic to animals and plants alike. One species complex within this genus, the Fusarium solani species complex (FSSC), is of particular concern due to its high numbers of pathogenic members. FSSC members are known to contribute significantly to plant, human and other animal fungal disease. One member of the FSSC, Fusarium keratoplasticum, is of particular ecological concern and has been implicated in low hatching success of endangered sea turtle eggs, as well as contribute to human and other animal Fusarium pathogenesis. Species-specific primers for molecular identification of F. keratoplasticum currently do not exist to our knowledge, making rapid identification, tracking and quantitation of this pathogenic fungus difficult. The objective of this study was to develop primers specific to F. keratoplasticum that could be applied to DNA from isolated cultures as well as total (mixed) DNA from environmental samples. RPB2 sequence from 109 Fusarium isolates was aligned and analysed to determine nucleotide polymorphisms specific to F. keratoplasticum useful for primer design. A set of primers were generated and found to be effective for identification of F. keratoplasticum from total DNA extracted from sand surrounding sea turtle nesting sites.

First data on microflora of loggerhead sea turtle (Caretta caretta) nests from the coastlines of Sicily

Caretta caretta is threatened by many dangers in the Mediterranean basin, but most are human-related. The purposes of this research were: (i) to investigate microflora in samples from six loggerhead sea turtle nests located on the Sicilian coast and (ii) to understand microbial diversity associated with nests, with particular attention to bacteria and fungi involved in failed hatchings. During the 2016 and 2018 summers, 456 eggs and seven dead hatchling from six nests were collected. We performed bacteriological and mycological analyses on 88 egg samples and seven dead hatchlings, allowing us to isolate: Fusarium spp. (80.6%), Aeromonas hydrophila (55.6%), Aspergillus spp. (27.2%) and Citrobacter freundii (9%). Two Fusarium species were identified by microscopy and were confirmed by PCR and internal transcribed spacer sequencing. Statistical analyses showed significant differences between nests and the presence/absence of microflora, whereas no significant differences were observed between eggs and nests. This is the first report that catalogues microflora from C . caretta nests/eggs in the Mediterranean Sea and provides key information on potential pathogens that may affect hatching success. Moreover, our results suggest the need for wider investigations over extensive areas to identify other microflora, and to better understand hatching failures and mortality related to microbial contamination in this important turtle species.

Newly emerging diseases of marine turtles, especially sea turtle egg fusariosis (SEFT), caused by species in the Fusarium solani complex (FSSC)

Sea turtles are presently considered severely endangered species that are historically threatened by many environmental factors. Recently, additional threats to sea turtles from two pathogenic species of fungi in the Fusarium solani species complex (F. falciforme and F. keratoplasticum) have been identified. These species infect marine turtle eggs, causing sea turtle egg fusariosis, and kill their embryos, with recent reports of hatch-failure in seven globally distributed species of endangered sea turtles (Caretta caretta, Chelonia mydas, Dermochelys coriaceae, Eretmochelys imbricata, Lepidochelys olivacea, Lepidochelys kempi and Natator depressus). Mycelia and spores of pathogenic species of Fusarium are produced in disturbed terrestrial soils and are transported to the ocean in coastal run off. We propose that these fungi grow on floating particles of plant tissues (leaves and wood), animal tissues, silt and plastics, which are carried by wind and currents and the turtles themselves to the beaches where the turtles lay their eggs.