Many fungal species grow through a
process of vesicle secretion that can be applied in a biotechnology setting to
make commercial or medical products. However, the details of this process are
unclear. Researchers in Japan used a high-speed imaging technique to visualize
hyphal growth in the fungus Aspergillus
nidulans. Several new features were uncovered, including the discovery that
different vesicle types move at different velocities.
Most fungi grow through the extension of
hyphae, which are fiber-like structures made of one or more cells encased
within a single, long cell wall. The growing tip of a hypha is loaded with
ChsB, a cell wall synthesis enzyme that helps to lengthen the cell wall. ChsB
is carried through the hypha by small cellular sacs called vesicles. In order
for hyphae to grow, the transport and release of ChsB by these vesicles needs
to be precisely timed-and exactly how this timing is achieved is unclear.
To address these shortcomings, the
researchers used a technique called high-speed pulse-chase imaging, which
allowed them to follow ChsB by fusing it to a marker emitting red fluorescent
light. After bleaching away background red light using a laser beam, a separate
beam was aimed at a single spot in the hypha, causing ChsB to fluoresce. The
team was then able to trace the movement of the fluorescent ChsB as vesicles
carried it around the hypha.
The technique resulted in minimal
background and allowed images to be taken, on average, every 50 milliseconds-a
level of precision not previously seen in hyphae. Correspondingly, the study
yielded many new insights into the timing of vesicle movement during fungal
growth.
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Posted by Dr. Tim Sandle
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Pharmaceutical Microbiology