A Perilipin Affects Lipid Droplet Homeostasis and Aerial Hyphal Growth, but Has Only Small Effects on Virulence in the Insect Pathogenic Fungus Beauveria bassiana

Abstract

Lipid assimilation, storage, and turnover impact growth, development, and virulence in many microbial pathogens including fungi. Perilipins are proteins associated with lipid droplets (LDs) that mediate their assembly and turnover. Here, we characterized the Beauveria bassiana (BbPlin1) perilipin. BbPlin1 expression was higher in minimal media than in rich media, and, using a BbPlin1::eGFP fusion protein, the protein was shown to be co–localized to LDs, with the high expression seen during infection and proliferation within the insect (Galleria mellonella) host that dramatically decreased to almost no expression during fungal outgrowth on cadavers including in conidia, but that BbPlin1 production resumed in the conidia once placed in nutrient–containing media allowing for germination and growth. Characterization of a targeted gene deletion strain (ΔBbPlin1) revealed a dramatic (>30%) reduction in cellular LD content, promotion of aerial hyphal growth, and a small decrease in virulence, with little to no effects on vegetative growth and stress responses. However, in the ΔBbPlin1 strain, expression of the complementary LD–associated caleosin gene, BbCal1, was enhanced under nutrient–poor conditions, although no changes in BbPlin1 expression were seen in a ΔBbCal1 strain and the expression of BbPlin1 in the ΔBbCal1 strain did not change LD patterns in cells. Transcriptome and RT–PCR analyses indicated increased expression of lipid metabolism–related genes, including triacylglyercol lipase 3, enoyl–CoA isomerase, and diacylglycerol–O–acetyl transferase in the BbPlin1 deletion mutant. Lipid profile analyses confirmed that the loss of BbPlin1 significantly reduced the cellular levels of contents of triacylglycerol, diacylglycerol, and phosphatidylethanolamine as compared to the wild–type strain. These results demonstrate the involvement of the B. bassiana perilipin in mediating lipid homeostasis, fungal aerial hyphal growth, and virulence, revealing critical cycling from high expression during nutrient utilization within host cadavers to low expression during growth on the surface of the cadaver during the infection process.

Characterization of an α-Amylase from the Honeybee Chalk Brood Pathogen Ascosphaera apis

“…Chalkbrood is a fungal disease of bee brood resulting from infection by spores of the ascomycete Ascosphaera apis [1,2]. Unlike some broad host range entomopathogenic fungi (e.g., Beauveria bassiana and Metarhizium anisopliae) that germinate and penetrate the cuticles of their insect hosts [3,4], A. apis spores must be consumed to infect larvae [5]. All larval castes are susceptible to infection.…”

“…Amylases are mainly classified into two major groups, αand β-, according to the anomeric sugar product resulting from the enzymatic reaction [18,19]. α-Amylases are endo-enzymes that catalyze the hydrolysis of α-D- (1,4) glycosidic linkages in starch and related carbohydrates [16], whereas β-amylases are exo-enzymes that catalyze the hydrolysis of α-1,4-glucan bonds in amylosaccharide chains from the non-reducing ends of substrates, including starch, glycogen, amylose, amylopectin, and other malto-oligosaccharides to successively release β-anomeric maltose [20,21].…”

The Elongator Subunit Elp3 Regulates Development, Stress Tolerance, Cell Cycle, and Virulence in the Entomopathogenic Fungus Beauveria bassiana

“…Growing hyphae then penetrate into the host integument via the combination of mechanical pressure and secretion of cuticle degrading enzymes, after which the fungus undergoes a dimorphic transition to produce single-celled, freely floating hyphal bodies in the insect hemocoel [ 30 , 31 , 32 ]. After depletion of the host nutrient in the hemolymph, the fungus works its way outwards, ultimately sporulating on the insect cadaver to complete its lifecycle [ 33 , 34 ]. Several parameters have been recognized as critical to the insect biological control potential of B. bassiana, including: conidial production (including yield, viability, and virulence); tolerances to abiotic/biotic stresses, especially oxidative, osmotic, heat, and UV; and the production of different virulence-related factors [ 35 , 36 ].…”