The pleiotropic functions of Intracellular hydrophobins in aerial hyphae and fungal spores

Higher fungi can rapidly produce large numbers of spores suitable for aerial dispersal. The efficiency of the dispersal and spore resilience to abiotic stresses correlate with their hydrophobicity provided by the unique amphiphilic and superior surface-active proteins–hydrophobins (HFBs)–that self-assemble at hydrophobic/hydrophilic interfaces and thus modulate surface properties. Using the HFB-enriched mold Trichoderma (Hypocreales, Ascomycota) and the HFB-free yeast Pichia pastoris (Saccharomycetales, Ascomycota), we revealed that the rapid release of HFBs by aerial hyphae shortly prior to conidiation is associated with their intracellular accumulation in vacuoles and/or lipid-enriched organelles. The occasional internalization of the latter organelles in vacuoles can provide the hydrophobic/hydrophilic interface for the assembly of HFB layers and thus result in the formation of HFB-enriched vesicles and vacuolar multicisternal structures (VMSs) putatively lined up by HFBs. These HFB-enriched vesicles and VMSs can become fused in large tonoplast-like organelles or move to the periplasm for secretion. The tonoplast-like structures can contribute to the maintenance of turgor pressure in aerial hyphae supporting the erection of sporogenic structures (e.g., conidiophores) and provide intracellular force to squeeze out HFB-enriched vesicles and VMSs from the periplasm through the cell wall. We also show that the secretion of HFBs occurs prior to the conidiation and reveal that the even spore coating of HFBs deposited in the extracellular matrix requires microscopic water droplets that can be either guttated by the hyphae or obtained from the environment. Furthermore, we demonstrate that at least one HFB, HFB4 in T. guizhouense, is produced and secreted by wetted spores. We show that this protein possibly controls spore dormancy and contributes to the water sensing mechanism required for the detection of germination conditions. Thus, intracellular HFBs have a range of pleiotropic functions in aerial hyphae and spores and are essential for fungal development and fitness.

Contributions of environmental and maternal transmission to the assembly of leaf fungal endophyte communities

Leaf fungal endophytes (LFEs) contribute to plant growth and responses to stress. Fungi colonize leaves through maternal transmission, e.g. via the seed, and through environmental transmission, e.g. via aerial dispersal. The relative importance of these two pathways in assembly and function of the LFE community is poorly understood. We used amplicon sequencing to track switchgrass ( Panicum virgatum ) LFEs in a greenhouse and field experiment as communities assembled from seed endophytes and rain fungi (integration of wet and dry aerial dispersal) in germinating seeds, seedlings, and adult plants. Rain fungi varied temporally and hosted a greater portion of switchgrass LFE richness (greater than 65%) than were found in seed endophytes (greater than 25%). Exposure of germinating seeds to rain inoculum increased dissimilarity between LFE communities and seed endophytes, increasing the abundance of rain-derived taxa, but did not change diversity. In the field, seedling LFE composition changed more over time, with a decline in seed-derived taxa and an increase in richness, in response to environmental transmission than LFEs of adult plants. We show that environmental transmission is an important driver of LFE assembly, and likely plant growth, but its influence depends on both the conditions at the time of colonization and plant life stage.

Carposina sasakii (peach fruit moth).

C. sasakii is a pest of rosaceous fruits in eastern Asia, and does not spread easily to the non-native areas and countries. C. sasakii has the potential to fly long distances, but usually flies only within and between canopies of fruit trees. Aerial dispersal to non-native areas has not been recorded. International trade of rosaceous fruits is a possible cause of spread of C. sasakii, but it is difficult for it to enter non-native countries under quarantine inspection. Even if C. sasakii enters non-native countries by international trade, it is not easy to establish a population, probably because the larvae in fruits cannot find a cocooning site near rosaceous plants after escaping from the fruits. However, C. sasakii has a strong impact on the management of rosaceous fruit orchards once a population is established. Damage to fruits can reach 100% in some cases in pears [Pyrus spp.] and 40-100% in apples [Malus spp.] if not controlled.

Phakopsora ampelopsidis (Ampelopsis rust fungus).

As currently defined (Ono, 2000), the rust fungus P. ampelopsidis is a pathogen of hosts in the genus Ampelopsis and perhaps in related genera in the Vitaceae, but not of the cultivated grapevine species of Vitis or the ornamental species in Parthenocissus. Plants in Ampelopsis occur in Asia from Japan to Turkey as well as in North America (USDA-ARS, 2009), but the rust is not known in Europe, and has not been reported on Ampelopsis in the Americas. Only in eastern Asia, where the medicinal uses of Ampelopsis species are being investigated (Kim et al., 2007; Zhang et al., 2008), is this rust a potential problem. It is most likely to be spread by aerial dispersal of urediniospores to nearer parts of Asia, where species in the host genus are distributed.

Intracellular accumulation and secretion of hydrophobin-enriched vesicles aid the rapid sporulation of molds

Fungi can rapidly produce large amounts of spores suitable for aerial dispersal. The hydrophobicity of spores is provided by the unique amphiphilic and superior surface-active proteins – hydrophobins (HFBs) – that self-assemble at hydrophobic/hydrophilic interfaces and thus change surface properties. Using the HFB-enriched mold Trichoderma and the HFB-free yeast Pichia pastoris, we revealed a distinctive HFB secretory pathway that includes an intracellular accumulation of HFBs in lipid bodies (LBs) that can internalize in vacuoles. The resulting vacuolar multicisternal structures (VMS) are stabilized by HFB layers that line up on their surfaces. These HFB-enriched VMSs can move to the periplasm for secretion or become fused in large tonoplast-like organelles. The latter contributes to the maintenance of turgor pressure required for the erection of sporogenic structures and rapid HFB secretion by squeezing out periplasmic VMSs through the cell wall. Thus, HFBs are essential accessory proteins for the development of aerial hyphae and colony architecture.

The Importance of a Filament-like Structure in Aerial Dispersal and the Rarefaction Effect of Air Molecules on a Nanoscale Fiber: Detailed Physics in Spiders’ Ballooning

Synopsis Many flying insects utilize a membranous structure for flight, which is known as a “wing.” However, some spiders use silk fibers for their aerial dispersal. It is well known that spiders can disperse over hundreds of kilometers and rise several kilometers above the ground in this way. However, little is known about the ballooning mechanisms of spiders, owing to the lack of quantitative data. Recently, Cho et al. discovered previously unknown information on the types and physical properties of spiders’ ballooning silks. According to the data, a crab spider weighing 20 mg spins 50–60 ballooning silks simultaneously, which are about 200 nm thick and 3.22 m long for their flight. Based on these physical dimensions of ballooning silks, the significance of these filament-like structures is explained by a theoretical analysis reviewing the fluid-dynamics of an anisotropic particle (like a filament or a high-slender body). (1) The filament-like structure is materially efficient geometry to produce (or harvest, in the case of passive flight) fluid-dynamic force in a low Reynolds number flow regime. (2) Multiple nanoscale fibers are the result of the physical characteristics of a thin fiber, the drag of which is proportional to its length but not to its diameter. Because of this nonlinear characteristic of a fiber, spinning multiple thin ballooning fibers is, for spiders, a better way to produce drag forces than spinning a single thick spider silk, because spiders can maximize their drag on the ballooning fibers using the same amount of silk dope. (3) The mean thickness of fibers, 200 nm, is constrained by the mechanical strength of the ballooning fibers and the rarefaction effect of air molecules on a nanoscale fiber, because the slip condition on a fiber could predominate if the thickness of the fiber becomes thinner than 100 nm.

Identification of a dynamic middle ear microbiome in healthy adults

Background The entrenched dogma of a sterile middle ear in health is incongruent with its periodic exposure to exhaled air when the tympanic (Eustachian) tube opens while swallowing, yawning or inhaling deeply. Tubal patency is brief but frequent to provide adequate aeration, equalize pressure across the eardrum and drain mucus down the sides of the oropharynx. It also provides a mechanism for aerial dispersal of microorganisms from the aerodigestive tract. Method We designed a pilot study and received institutional approval to collect otic secretions that naturally drain on the sides of the oropharynx, behind the palatopharyngeal arch. This protocol bypassed the need to surgically access the middle ear through or around the eardrum, allowed us to collect samples from individuals with no underlying otic conditions, and prevented sample cross-contamination. As controls, we also collected samples from the center of the oropharynx and buccal mucosae seeded by saliva, which may serve as sources of microbial dispersal into the middle ear. Results We sequenced 16S rRNA-V4 amplicons from otic, oropharyngeal and buccal samples collected from a cohort of 19 healthy young adults. The survey identified in the otic samples a diverse bacterial community with many oropharyngeal and buccal keystone taxa and most of the functional traits of the neighboring oral microbiomes. Neutral community models predicted a large contribution of oral dispersal to the composition of the otic microbiome as well as several taxa responsive to positive selection. This was further supported by the enrichment in the otic communities of obligate anaerobes of Bacteroidetes and Fusobacteria over facultative anaerobic Proteobacteria and Firmicutes. Furthermore, the prevalence of the anaerobic members decreased with the more frequent otic aeration predicted from the equalization training of scuba divers recruited to the study. Conclusions These results challenge the long held view of a sterile middle ear and suggest instead that frequent seeding with oral microbes supports the establishment of a rich and robust otic community dynamically adapted to the episodic ventilation of the tympanic space.