Chemical study on Paenibacillus odorifer, a bacterial species isolated from lichen

Abstract

Recent studies have admitted that bacterial communities were an important united partner of mini-ecosystem lichen symbiosis. Lichen, moreover, is also a rich source of new bacterial lineages and novel bacterial compounds. Therefore, microorganism communities isolated from lichens became a significant subject as a great potential of natural product discovery. Paenibacillus odorifer, a bacterium belonging to Firmicutes, was isolated from Rhizocarpon geographicum, a particular popular crust-forming rock lichen. Assessing its optimal growth conditions was conducted to improve its metabolite production yield by measure of optical density (OD) and by analysis of its chemical profile via TLC, HPLC, LC-MS. Firstly, the parameters chosen for optimal culture were kind of medium, pH and temperature. Results revealed that the growth of P. odorifer was better at 250C using Gym Streptomyces liquid medium supplemented with CaCO3 at pH=7. Secondly, the fermentation was launched by applying the best conditions of bacterial growth. After the 3-day culture using a bioreactor, the supernatant and bacterial cells were separated by centrifugation and organic compounds were absorbed from supernatant by XAD-7 resin. The desorption from resin was carried out through several stages to collect raw extract. TLC, HPLC and LC-MS analyses highlighted that this extract was a rich source of metabolites. Then, the crude extract was fractionated via flash chromatography on a 40 g C18 reversed-phase column, using a gradient solvent system of CH3CN-H2O at 15 mL/min flow rate in 75 min. Two diketopiperazines were isolated from the fractions by applying semi-preparative HPLC (Prevail C18 column, various ratios of CH3CN) such as cyclo(L-Phe-L-Val) and cyclo(L-Phe-L-Ile). Correspondingly, fermentation of P. odorifer could produce valuable compounds for future research.