Resistant ticks inhibit Metarhizium infection prior to haemocoel invasion by reducing fungal viability on the cuticle surface

Abstract

We studied disease progression of, and host responses to, four species in the Metarhizium anisopliae complex expressing green fluorescent protein (GFP). We compared development and determined their relative levels of virulence against two susceptible arthropods, the cattle tick Rhipicephalus annulatus and the lepidopteran Galleria mellonella, and two resistant ticks, Hyalomma excavatum and Rhipicephalus sanguineus. Metarhizium brunneum Ma7 caused the greatest mortality of R. annulatus, Metarhizium robertsii ARSEF 2575 and Metarhizium pingshaense PPRC51 exhibited intermediate levels of virulence, and Metarhizium majus PPRC27 caused low mortality of cattle ticks. Conidia of all four species germinated on all hosts examined, but on resistant hosts, sustained hyphal growth was inhibited and GFP emission steadily and significantly decreased over time, suggesting a loss of fungal viability. Cuticle penetration was observed only for the three most virulent species infecting susceptible hosts. Cuticles of resistant and susceptible engorged female ticks showed significant increases in red autofluorescence at sites immediately under fungal hyphae. This is the first report (i) of tick mortality occurring after cuticle penetration but prior to haemocoel colonization and (ii) that resistant ticks do not support development of Metarhizium germlings on the outer surface of the cuticle. Whether reduced Metarhizium viability on resistant tick cuticles is due to antibiosis or limited nutrient availability is unknown.

Enhanced detection of Rickettsia species in Ixodes pacificus using highly sensitive fluorescence in situ hybridization coupled with Tyramide Signal Amplification

“…Our FISH results confirmed previous reports that the low signal to noise ratio due to autofluorescence of tick tissues made it difficult to visualize bacteria using fluorescently labeled probes (Epis et al, 2013; Hammer et al, 2001; Ment et al, 2012). The low signal to noise ratio in FISH could be due to weak emission signals of the probes and the low ribosome content of bacteria in tissues of field-collected samples (Lenaerts et al, 2007; Zwirglmaier, 2005).…”

Secondary metabolite gene clusters in the entomopathogen fungus Metarhizium anisopliae: genome identification and patterns of expression in a cuticle infection model

“…These results point to a drastic change between the metabolic profiles of early and late infection. The Metarhizium infection process is dynamic and may end in arthropod or fungal death [90]. Once the fungus adheres to a host, rapid morphological and transcriptional changes occur, including the expression of several virulence factors [91].…”

“…Once the fungus adheres to a host, rapid morphological and transcriptional changes occur, including the expression of several virulence factors [91]. Ment and coworkers (2012) showed that after 3 or 4 days of attachment to a suitable host, Metarhizium kills the host [90], switching to a saprophytic state, and virulence determinant expression is attenuated [2]. Conversely, in an unsuccessful infection scenario, the fungus will exhaust the endogenous spore nutrient reserves at 3 or 4 days post-cuticle adhesion while attempting to circumvent host defenses, resulting in the demise of the pathogen [90].…”

Phylogenetic status and pathogenicity of Metarhizium majus isolated from a fruit beetle larva in Japan

“…According to previous studies, MALC or M. majus has been isolated from at least three species of fruit beetle (Scarabaeidae, Cetoniinae, and Cetoniini) other than Pos: C. aurata in France, P. brevitarsis seulensis in Korea, and Pachnoda interrupta in Ethiopia (Fargues and Robert 1983;Choi et al 2003;Ment et al 2012). Among the three foreign isolates, the Korean isolate KMA-1 is most likely to be the same pathotype as Hn1 and appears to be closely related to Hn1 because of the similarity in host species and the close geographical origin.…”

“…The DNA sequence from the intergenic transcribed spacer region of rDNA from KMA-1 (GenBank accession number: AY237118) was similar but not identical to that of Hn1 (GenBank accession number: AB712254), differing by one substitution and a 1-bp indel. Among the three foreign fruit beetle pathogens, only the Ethiopian isolate PRC27 was identified as M. majus on the basis of the sequence of 5′-EF1-α (Ment et al 2012). PRC27 differs from Hn1 in nucleotide variation, and PRC27 is relatively closely related to the group of isolates from Oryctes sp.…”