Lignocellulose is a promising renewable resource for producing platform chemicals, such as acetone, butanol, and ethanol, via ABE fermentation by solventogenic clostridia. This study investigates the effects of common lignocellulose derived inhibitory compounds: ferulic acid, coumaric acid, and furfural on Clostridium beijerinckii. Dual-staining with propidium iodide and CFDA, combined with flow cytometry, was employed to assess physiological variability. The results showed that phenolic acid-induced stress helped maintain a higher proportion of viable cells during the production phase, enhancing solvent yields and reducing sporulation. At 0.4 g/L, ferulic and coumaric acids did not reduce cell viability; however, coumaric acid exposure led to an acid-crash profile. Conversely, a more robust inoculum exposed to both phenolic acids simultaneously exhibited effects similar to ferulic acid alone, including slower viability decline, reduced growth and sporulation, and improved solvent production. Furfural exposure at 1.5 g/L resulted in immediate viability loss in 20% of the population, though the overall decline accompanied by the highest sporulation rate occurred later than in the control. Additionally, furfural transformation was slower, suppressing butyrate production and reducing solvent production by 13%. This study suggests that delaying cell death mechanism may explain the stimulatory effects of inhibitors, advancing lignocellulose use in the future.

• Keywords
• Clostridium beijerinckii, ABE, Butanol, Carboxyfluorescein diacetate, Cytometry, Lignocellulose inhibitors, Viability,
• Publication type
• Journal Article MeSH

BACKGROUND: This paper brings new information about the genome and phenotypic characteristics of Pantoea agglomerans strain DBM 3797, isolated from fresh Czech hop (Humulus lupulus) in the Saaz hop-growing region. Although P. agglomerans strains are frequently isolated from different materials, there are not usually thoroughly characterized even if they have versatile metabolism and those isolated from plants may have a considerable potential for application in agriculture as a support culture for plant growth. METHODS: P. agglomerans DBM 3797 was cultured under aerobic and anaerobic conditions, its metabolites were analyzed by HPLC and it was tested for plant growth promotion abilities, such as phosphate solubilization, siderophore and indol-3-acetic acid productions. In addition, genomic DNA was extracted, sequenced and de novo assembly was performed. Further, genome annotation, pan-genome analysis and selected genome analyses, such as CRISPR arrays detection, antibiotic resistance and secondary metabolite genes identification were carried out. RESULTS AND DISCUSSION: The typical appearance characteristics of the strain include the formation of symplasmata in submerged liquid culture and the formation of pale yellow colonies on agar. The genetic information of the strain (in total 4.8 Mb) is divided between a chromosome and two plasmids. The strain lacks any CRISPR-Cas system but is equipped with four restriction-modification systems. The phenotypic analysis focused on growth under both aerobic and anaerobic conditions, as well as traits associated with plant growth promotion. At both levels (genomic and phenotypic), the production of siderophores, indoleacetic acid-derived growth promoters, gluconic acid, and enzyme activities related to the degradation of complex organic compounds were found. Extracellular gluconic acid production under aerobic conditions (up to 8 g/l) is probably the result of glucose oxidation by the membrane-bound pyrroloquinoline quinone-dependent enzyme glucose dehydrogenase. The strain has a number of properties potentially beneficial to the hop plant and its closest relatives include the strains also isolated from the aerial parts of plants, yet its safety profile needs to be addressed in follow-up research.

• Keywords
• Pantoea agglomerans, genome characterization, gluconic acid, hops endophyte, plant growth promotion,
• Publication type
• Journal Article MeSH