Lignin intermediates lead to phenyl acid formation and microbial community shifts in meso- and thermophilic batch reactors

Effects of denitrification on speciation and redistribution of arsenic in estuarine sediments

Microbially-mediated redox processes involving arsenic (As) and its host minerals significantly contribute to the mobilization of As in estuarine sediments. Despite its significance, the coupling between As dynamics and denitrification processes in these sediments is not well understood. This study employed sequential sediment extractions and simultaneous monitoring of dissolved iron (Fe), nitrogen (N), and sulfur (S) to investigate the impact of nitrate (NO3-) on the speciation and redistribution of As, alongside changes in microbial community composition. Our results indicated that NO3- additions significantly enhance anaerobic arsenite (As(III)) oxidation, facilitating its immobilization by increased adsorption onto sediment matrices in As-contaminated estuarine settings. Furthermore, NO3- promoted the conversion of As bound to troilite (FeS) and pyrite (FeS2) into forms associated with Fe oxides, challenging the previously assumed stability of FeS/FeS2-bound As in such environments. Continuous NO3- additions ensured As and Fe oxidation, thereby preventing their reductive dissolution and stabilizing the process that reduces As mobility. Changes in the abundance of bacterial communities and correlation analyses revealed that uncultured Anaerolineaceae and Thioalkalispira may be the main genus involved in these transformations. This study underscores the critical role of NO3- availability in modulating the biogeochemical cycle of As in estuarine sediments, offering profound insights for enhancing As immobilization techniques and informing environmental management and remediation strategies in As-contaminated coastal regions.

Effects of phenyl acids on different degradation phases during thermophilic anaerobic digestion

Aromatic compounds like phenyl acids (PA) can accumulate during anaerobic digestion (AD) of organic wastes due to an increased entry of lignocellulose, secondary plant metabolites or proteins, and thermodynamic challenges in degrading the benzene ring. The effects of aromatic compounds can be various – from being highly toxic to be stimulating for methanogenesis – depending on many parameters like inoculum or molecular characteristics of the aromatic compound. To contribute to a better understanding of the consequences of PA exposure during AD, the aim was to evaluate the effects of 10 mM PA on microbial communities degrading different, degradation phase–specific substrates in thermophilic batch reactors within 28  days: Microcrystalline cellulose (MCC, promoting hydrolytic to methanogenic microorganisms), butyrate or propionate (promoting syntrophic volatile fatty acid (VFA) oxidisers to methanogens), or acetate (promoting syntrophic acetate oxidisers to methanogens). Methane production, VFA concentrations and pH were evaluated, and microbial communities and extracellular polymeric substances (EPS) were assessed. The toxicity of PA depended on the type of substrate which in turn determined the (i) microbial diversity and composition and (ii) EPS quantity and quality. Compared with the respective controls, methane production in MCC reactors was less impaired by PA than in butyrate, propionate and acetate reactors which showed reductions in methane production of up to 93%. In contrast to the controls, acetate concentrations were high in all PA reactors at the end of incubation thus acetate was a bottle-neck intermediate in those reactors. Considerable differences in EPS quantity and quality could be found among substrates but not among PA variants of each substrate. Methanosarcina spp. was the dominant methanogen in VFA reactors without PA exposure and was inhibited when PA were present. VFA oxidisers and Methanothermobacter spp. were abundant in VFA assays with PA exposure as well as in all MCC reactors. As MCC assays showed higher methane yields, a higher microbial diversity and a higher EPS quantity and quality than VFA reactors when exposed to PA, we conclude that EPS in MCC reactors might have been beneficial for absorbing/neutralising phenyl acids and keeping (more susceptible) microorganisms shielded in granules or biofilms.

Low-Temperature Biodegradation of Lignin-Derived Aromatic Model Monomers by the Cold-Adapted Yeast Rhodosporidiobolus colostri Isolated from Alpine Forest Soil

The contribution of cold-adapted yeasts to the emerging field of lignin biovalorization has not yet been studied. The red-pigmented basidiomycetous yeast strain Rhodosporidiobolus colostri DBVPG 10655 was examined for its potential to degrade five selected lignin-derived aromatic monomers (syringic acid, p-coumaric acid, 4-hydroxybenzoic acid, ferulic acid, and vanillic acid). The strain utilized p-coumaric acid, 4-hydroxybenzoic acid, and ferulic acid not only as the sole carbon source; full biodegradation occurred also in mixtures of multiple monomers. Vanillic acid was not utilized as the sole carbon source, but was degraded in the presence of p-coumaric acid, 4-hydroxybenzoic acid, and ferulic acid. Syringic acid was utilized neither as the sole carbon source nor in mixtures of compounds. Biodegradation of lignin-derived aromatic monomers was detected over a broad temperature range (1–25 °C), which is of ecological significance and of biotechnological relevance.

A survey of greenhouse gases production in central European lignites

Due to changes in the energy market, it is projected that lignite excavation will be reduced in the near future. Cessation of exploitation is associated with restitution of natural water conditions and flooding of the resources left in the mines. Flooded lignite mines are a potential source of greenhouse gases (GHG) (CH_4, CO₂ and N₂O), which should be monitored due to growing environmental concerns. Here, we aim to recognize GHG release from the lignites collected from the main deposits of Poland, Slovenia and Serbia. GHG production was studied along with a range of physical and chemical parameters that are crucial for microbial growth and activity. The microcosm experiments showed that the main gas emitted from the lignites was carbon dioxide. Daily CO₂ production was highly variable. The highest values were recorded for detroxylitic lignite collected from the Konin deposit (402.05 nmol CO₂ g^-1 day^-1) while the lowest were for the Kolubara xylitic lignite (19.64 nmol CO₂ g^-1 day^-1). Methane production was much lower and ranged from nearly zero to 66.75 nmol g dry mass^-1 d^-1. Nitrous oxide production was not detected. It was found that CO₂ production, being a general measure of microbial activity, was positively affected by NO₃^- concentration and redox potential. With respect to methane formation, the lower atmospheric oxygen exposure of the sample from the Velenje underground mine compared to the samples from the opencast mines has been identified as a possible cause of the high methane production. The overall global warming potential (GWP) of the gases released by xylitic lignite was lowest among the samples. Preferential extraction of the detritic lignites is suggested as a means to reduce GHG emissions from the abandoned lignite mines.