Abstract
Biotechnologists are interested in thermo tolerant fungi to manufacture enzymes active and stable at high temperatures, because they provide improved catalytic efficiency, strengthen enzyme substrate interactions, accelerate substrate enzyme conversion rates, enhance mass transfer, lower substrate viscosity, lessen contamination risk and offer the potential for enzyme recycling. Members of the genus Aspergillus live a wide variety of lifestyles, some embrace GRAS status routinely employed in food processing while others such as Aspergillus fumigatus are human pathogens. A. fumigatus produces melanins, pyomelanin protects the fungus against reactive oxygen species and DHN melanin produced by the pksP gene cluster confers the gray-greenish color. pksP mutants are attenuated in virulence. Here we report on the genomic DNA sequence of a thermo tolerant albino Aspergillus isolated from rain forest composted floors. Unexpectedly, the nucleotide sequence was 95.7% identical to the reported by Aspergillus fumigatus Af293. Genome size and predicted gene models were also highly similar, however differences in DNA content and conservation were observed. The albino strain, classified as Aspergillus fumigatus var. niveus, had 160 gene models not present in A. fumigatus Af293 and A. fumigatus Af293 had 647 not found in the albino strain. Furthermore, the major pigment generating gene cluster pksP appeared to have undergone genomic rearrangements and a key tyrosinase present in many aspergilli was missing from the genome. Remarkably however, despite the lack of pigmentation A. fumigatus var. niveus killed neutropenic mice and survived macrophage engulfment at similar rates as A. fumigatus Af293.
Highlights
Aspergillus nidulans FGSC A1228 and Aspergillus fumigatus Af293 was purchased from the Fungal Genetics Stock Center (FGSC, St Louis, MO) and Aspergillus awamori strain ATCC 22342 was a gift from the National Renewable Energy Laboratory (NREL, Golden, CO)
Single colony agar plate assays were generated by single-spot inoculation at the center of a complete medium agar plate with fresh conidia from A. fumigatus var. niveus, A. fumigatus Af293, A. awamori and A. nidulans
The high degree of genomic DNA (gDNA) sequence similarity of the albino Aspergillus with A. fumigatus isolates and related species such as Neosartorya fischeri, lead us to compare in Figure 2A the morphology of condiophore vesicles and uniseriate phialide that were almost identical between strains
Summary
The search for thermo tolerant organisms that manufacture enzymes active and stable at high temperatures has been investigated in fungi, (Berka et al, 2011; Brink et al, 2011; Houbraken et al, 2012; Morgenstern et al, 2012), bacteria (Chang and Yao, 2011; Mingardon et al, 2011; Wang et al, 2011; dos Santos et al, 2012; Bhalla et al, 2013; Sato and Atomi, 2013) and archaea (Cavicchioli et al, 2011; Wackett, 2011; Cadillo-Quiroz et al, 2012; Davidova et al, 2012). The genus Aspergillus groups a large number of species conveying a wide variety of lifestyles reciprocally beneficial and detrimental to humans (Gibbons and Rokas, 2013). Some species embrace GRAS (generally regarded as safe) status routinely employed for hundreds of years in food processing while others such as Aspergillus fumigatus are serious human pathogens causing aspergillosis (Latgé, 2001). Within the group of fungi that detrimentally affect humans, thermotolerance appears as a determining factor necessary to establish a pathogenic relationship (Casadevall, 2007). Humans have powerful innate immune mechanisms and pathogenic fungi possess the ability to withstand the negative effects of innate immune systems that include microbicidal peptides, oxidative bursts, phagocytic cells, and nutrient deprivation (Casadevall, 2007)
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