Investigating Physical and Chemical Interaction of Aspergillus terreus Spores for Changes in Morphology and Physiology

It has been widely reported that in filamentous fungi, spore inoculum size affects culture morphology and secondary metabolite production. The reasons for this, however, have not been investigated thus far.

There are two possible explanations as to why spore inoculum size affects fungal morphology, growth and productivity. Firstly, a quorum sensing phenomenon (QS). In this case, after population densities reach a certain threshold, signalling chemicals secreted into the environment effect expression of specific genes leading to a range of physiological responses. Secondly, due to physical spore-to-spore contact, communication may develop that could trigger a physical response, altering morphology and productivity.

To explore these hypotheses, research was split into two parts: the first “supplementation”, the addition of known quorum sensing molecules butyrolactone I, tyrosol and farnesol, alongside other chemicals expressed in literature as having potential effects on the physiology and morphology of a microbial culture. Furthermore, supplements from Aspergillus terreus MUCL 38669 obtained from I) spore supernatant, II) concentrated spore supernatant via freeze drying (FDSS) and III) high spore culture supernatants from 72-hour liquid cultures, were added to various concentrations of A. terreus spore inocula. The second part investigated effects of physical contact between spores by increasing spore interactions through sonication of spore suspensions and also, altering the physical space in which spores are confined to during growth, thereby forcing spore to spore contact.

Investigations showed behaviours similar to cultures affected by QS process. These included morphological changes and increased productivities. Additions of 0.01M farnesol to (low) spore inoculum concentrations of 1x103 spores/mL altered culture morphology to that seen of cultures of 1x107 spores/mL (high), lovastatin production also increased by 1208%. Similarly, the morphology of low spore cultures supplemented with FDSS were that of high spore cultures and lovastatin production increased by 67%. Sonication had no effect on cultures, however, confinement evoked changes in morphological characteristics and germination times of the culture.