Effects of Simulated Microgravity on the Proteome and Secretome of the Polyextremotolerant Black Fungus Knufia chersonesos

Abstract

Black fungi are a group of melanotic microfungi characterized by remarkable polyextremotolerance. Due to a broad ecological plasticity and adaptations at the cellular level, it is predicted that they may survive in a variety of extreme environments, including harsh niches on Earth and Mars, and in outer space. However, the molecular mechanisms aiding survival, especially in space, are yet to be fully elucidated. Based on these premises, the rock-inhabiting black fungus Knufia chersonesos (Wt) and its non-melanized mutant (Mut) were exposed to simulated microgravity—one of the prevalent features characterizing space conditions—by growing the cultures in high-aspect-ratio vessels (HARVs). Qualitative and quantitative proteomic analyses were performed on the mycelia and supernatant of culture medium (secretome) to assess alterations in cell physiology in response to low-shear simulated microgravity (LSSMG) and to ultimately evaluate the role of cell-wall melanization in stress survival. Differential expression was observed for proteins involved in carbohydrate and lipid metabolic processes, transport, and ribosome biogenesis and translation via ribosomal translational machinery. However, no evidence of significant activation of stress components or starvation response was detected, except for the scytalone dehydratase, enzyme involved in the synthesis of dihydroxynaphthalene (DNH) melanin, which was found to be upregulated in the secretome of the wild type and downregulated in the mutant. Differences in protein modulation were observed between K. chersonesos Wt and Mut, with several proteins being downregulated under LSSMG in the Mut when compared to the Wt. Lastly, no major morphological alterations were observed following exposure to LSSMG. Similarly, the strains’ survivability was not negatively affected. This study is the first to characterize the response to simulated microgravity in black fungi, which might have implications on future astrobiological missions.

The International Space Station Environment Triggers Molecular Responses in Aspergillus niger

“…Observed, alterations in proteins involved in carbohydrate metabolism upon exposure to space conditions stay in agreement with previous studies of A. niger JSC-093350089 ( Romsdahl et al, 2018 ), and other filamentous fungi, including Aspergillus fumigatus ( Blachowicz et al, 2019a , b ) and A. nidulans ( Romsdahl et al, 2019 ). Similarly, a black fungus Knufia chersonesos exposed to low-shear simulated microgravity (LSSMG) also exhibited differential expression of proteins involved in carbohydrate metabolism ( Tesei et al, 2021 ). On the other hand, a yeast, Candida albicans, exposed to spaceflight environment on the “SJ-10” satellite for 12 days showed decreased abundance of proteins involved in carbon metabolism, suggesting that yeast and filamentous fungi differ in adaptive responses to space environment ( Wang et al, 2020 ).…”

Colony growth and biofilm formation of Aspergillus niger under simulated microgravity

“…For example, previous studies with submerged liquid cultures of A. niger under low-shear modeled microgravity in the High Aspect Ratio Vessel (HARV), at a slow-rotation of 25 rpm, found no significant changes in spore germination, mycelium growth or cell wall integrity (Sathishkumar et al, 2014). Interestingly, further HARV studies at 30 rpm with the black fungus Knufia chersonesos found that low-shear modeled microgravity induced changes in the regulation of the DHN-melanin biosynthesis pathway (Tesei et al, 2021). Another study also reported that A. niger growth was not inhibited in a 3-D clinostat (Yamazaki et al, 2012).…”

Growth Behavior and Transcriptome Profile Analysis of Proteus mirabilis Strain Under Long- versus Short-Term Simulated Microgravity Environment

“…MG is defined as a state of weightlessness that occurs due to decreased physical force exerted by gravity, where gravity ranges from 10 –3 to 10 –6 g (Bijlani et al 2020). There is general agreement that MG is a crucial factor influencing microbial physiology in the space capsule during flight missions ( Tesei et al 2021 ). Due to technological and logistical hurdles, the microbial experiments under true MG in space stations are minimal.…”