Investigation of fungal growth and its influence on the permeability of the oceanic crust - Method Development using Penicillium Rubens

Abstract

The deep biosphere within the oceanic crust is a tantalizing frontier of the geomicrobiology field with many unanswered questions owing to great challenges that need to be overcome when investigating this habitat. Fungi have been proven to be part of this intricate ecosystem on multiple occasions. And even though fungal communities make up the majority of the found body fossils in the deep biosphere, there is still a lack of studies investigating fungi in this habitat. With their many abilities the fungi exert great influence on their environment in various ways, not least of which is that they may also have a significant influence on the alteration and the permeability of the crust. Using a strain of Penicillium rubens a novel experimental method using a custom-build Parr flow-through autoclave was developed to investigate the potential influence of the growth of fungi on the permeability of the crust. The results of the experiments indicate a strong influence of microbial growth on the reduction of the permeability. A potential inversed trend between the extent of permeability reduction and pressure was noted. However, in some experiments contamination with bacteria was observed, which could also account for the more pronounced decrease. To establish the parameters for the permeability experiments, syringe pump experiments were conducted to assess the growth within a certain timeframe and under certain conditions. To estimate the growth and evaluate the connection between biomass quantity and permeability decrease, two methods for biomass estimations were explored: Loss on ignition and PLS regression models based on the autofluorescence of ergosterol. Both estimation methods have proven to be inadequate to estimate the biomass amount for these experiments. A likely reason for this is that these methods are not robust enough for the low amounts of biomass obtained in these experiments.