Background:
Chitin is the main component of fungal, protozoan and helminth cell wall. They
help to maintain the structural and functional characteristics of these organisms. The chitin wall is dynamic
and is repaired, rearranged and synthesized as the cells develop. Active synthesis can be noticed
during cytokinesis, laying of primary septum, maintenance of lateral cell wall integrity and hyphal tip
growth. Chitin synthesis involves coordinated action of two enzymes namely, chitin synthase (that lays
new cell wall) and chitinase (that removes the older ones). Since chitin synthase is conserved in different
eukaryotic microorganisms that can be a ‘soft target’ for inhibition with small molecules. When
chitin synthase is inhibited, it leads to the loss of viability of cells owing to the self- disruption of the
cell wall by existing chitinase.
Methods:
In the described study, small molecules from plant sources were screened for their ability to
interfere with hyphal tip growth, by employing Hyphal Tip Burst assay (HTB). Aspergillus niger was
used as the model organism. The specific role of these small molecules in interfering with chitin synthesis
was established with an in-vitro method. The enzyme required was isolated from Aspergillus niger
and its activity was deduced through a novel method involving non-radioactively labelled substrate. The
activity of the potential lead molecules were also checked against Candida albicans and Caenorhabditis
elegans. The latter was adopted as a surrogate for the pathogenic helminths as it shares similarity with
regard to cell wall structure and biochemistry. Moreover, it is widely studied and the methodologies are
well established.
Results:
Out of the 11 compounds and extracts screened, 8 were found to be prospective. They were
also found to be effective against Candida albicans and Caenorhabditis elegans.
Conclusion:
Purified Methyl Ethyl Ketone (MEK) Fraction1 (F1) of Coconut (Cocos nucifera) Shell
Extract (COSE) was found to be more effective against Candida albicans with an IC50 value of 3.04
μg/mL and on L4 stage of Caenorhabditis elegans with an IC50 of 77.8 μg/mL.
Evidence for an arginine‐dependent route for the synthesis of
NO
in the model filamentous fungus
Aspergillus nidulans
