# In Vitro Modeling of Mycelium Biomass Growth Kinetics of the Novel Fungicolous Species Xylaria karsticola NBIMCC 9097, with Insights into Its Antimicrobial Potential

## TL;DR

A rare fungus called Xylaria karsticola was studied for its growth and ability to fight microbes, showing promising antimicrobial properties.

## Contribution

This study provides the first in vitro growth modeling and antimicrobial evaluation of the novel fungicolous species Xylaria karsticola.

## Key findings

- Optimized media increased biomass yields to 20.11 and 23.25 g/dm³ in MCM and MYB media, respectively.
- Hexane and ethyl acetate extracts showed strong antimicrobial activity against Pseudomonas aeruginosa and several yeast species.
- Water biomass extract exhibited the lowest MIC of 0.02 mg/cm³ against Saccharomycodes ludwigii.

## Abstract

Xylaria karsticola NBIMCC 9097 is a recently described and rare fungicolous species originating from Bulgaria. Understanding its growth behavior and bioactive potential is essential for evaluating its biotechnological and pharmaceutical relevance. In the presented study, we model the in vitro growth kinetics of X. karsticola mycelium under submerged cultivation and assess its antimicrobial activity. Optimization of MCM and MYB media markedly increased biomass yields to 20.11 and 23.25 g/dm3, respectively, compared with non-optimized media (9.9 ± 0.21 and 10.8 ± 0.28 g/dm3). The maximum specific growth rate was higher in the MCM (0.803 ± 0.004 h−1) in comparison with the MYB medium (0.711 ± 0.003 h−1); however, the MYB medium supported greater biomass accumulation and more efficient substrate utilization, reflected by a higher utilization coefficient (0.9900 ± 0.001 versus 0.9644 ± 0.005). The antimicrobial activity was evaluated using agar disk diffusion and minimum inhibitory concentration assays against Gram-positive and Gram-negative bacteria and yeasts. Hexane and ethyl acetate extracts were most effective against Pseudomonas aeruginosa ATCC 9027 (MIC 0.067 and 0.059 mg/cm3), while notable anti-yeast activity was observed, particularly against Wickerhamomyces anomalus, Saccharomycodes ludwigii, and Pichia membranifaciens. The lowest MIC (0.02 mg/cm3) was recorded for the water biomass extract against S. ludwigii indicating potent antimicrobial activity against the tested microorganism. These findings identify X. karsticola as a potential source of antimicrobial metabolites and provide a strong motivation for comprehensive metabolomic profiling and systematic optimization of its cultivation.