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Bio-electrochemical Systems (BES), particularly Microbial Fuel Cells (MFC), have emerged as promising technologies in environmental biotechnology. This study focused on optimizing the anode bacterial culture immobilization process to enhance BES performance. The investigation combines and modifies two key immobilization methods: covalent bonding with glutaraldehyde and inclusion in a chitosan gel in order to meet the criteria and requirements of the bio-anodes in MFC. The performance of MFCs with immobilized and suspended cultures was compared in parallel experiments. Both types showed similar substrate utilization dynamics with slight advantage of the immobilized bio-anode considering the lower concentration of biomass. The immobilized MFC exhibited higher power generation and metabolic activity, as well. Probably, this is due to improved anodic respiration and higher coulombic efficiency of the reactor. Analysis of organic acids content supported this conclusion showing significant inhibition of the fermentation products production in the MFC reactor with immobilized anode culture., (© 2024 Walter de Gruyter GmbH, Berlin/Boston.)

Taxonomic identification of three newly isolated Antarctic fungal strains by their 18S rDNA sequences revealed their affiliation with Aspergillus fumigatus. Phenol (0.5 g/l) as the sole carbon source was completely degraded by all strains within less than two weeks. Intracellular activities of three key enzymes involved in the phenol catabolism were determined. Activities of phenol hydroxylase (EC 1.14.13.7), hydroquinone hydroxylase (EC 1.14.13.x), and catechol 1,2-dioxygenase (EC 1.13.11.1) varied significantly between strains. The rates of phenol degradation in the three strains correlated best with the activity of catechol 1,2-dioxygenase. Six pairs of oligonucleotide primers were designed on the basis of the Aspergillus fumigatus Af293 genome sequence (NCBI Acc. No. XM_743491.1) and used to amplify phenol hydroxylase-related gene sequences. DNA sequences of about 1200 bp were amplified from all three strains and found to have a high degree of sequence identity with the corresponding gene of Aspergillus fumigatus Af293.

The ability of the white rot fungus Trametes versicolor strain 1 to degrade and utilize methylated phenols (cresols) was established for the first time in a medium not containing any other carbon components. The data obtained demonstrated the better potential of the strain to assimilate p-cresol instead of o- or m- cresol. The 0.5 g/l p-cresol provided was degraded in full after 96 h. The effect of a dual substrate mixture (0.3 g/l phenol + 0.2 g/l p-cresol) on the growth behavior and degradation capacity of the investigated strain was examined. The cell-free supernatants were analyzed by HPLC. It was established that the presence of p-cresol had not prevented complete phenol degradation but had a significant delaying effect on the phenol degradation dynamics. Phenol hydroxylase, catechol 1.2-dioxygenase and cis,cis-muconate cyclase activities were obtained in conditions of single and mixed substrates cultivation. The influence of different phenolic substrates on phenol hydroxylase activity in Trametes versicolor 1 was established. The mathematical models describing the dynamics of single substrates' utilization as well as the mutual influence of phenol and p-cresol in the mixture were developed on the bases of Haldane kinetics. The estimated interaction coefficients (I(ph/cr) = 4.72, I(cr/ph) = 7.46) demonstrated the significant inhibition of p-cresol on phenol biodegradation and comparatively low level of influence of phenol presence on the p-cresol degradation. Molecular 18S RNA gene taxonomy of the investigated strain was performed.

In an attempt to estimate the occurrence of phenol hydroxylase-related gene sequences we performed a dot blot hybridization assay with DNA from phenol utilizing Trichosporon cutaneum R57 strain NBIMCC 2414 and microbial isolates from different wastewaters. The used oligonucletides were homologous to the 5'-end of TORPHD locus (NCBI)-coding phenol hydroxylase in Trichosporon cutaneum ATCC 46490 and to the 5'-end of TORCCMLE locus (NCBI)-coding cis,cis-muconate-lactonizing enzyme in Trichosporon cutaneum ATCC 58094. Two microbial strains, Escherichia coli JM 109 and Lactobacillus acidophilus ATCC 4356, incapable to degrade phenol were used as negative controls. We established the presence of hybridization with both used oligonucleotide probes in T. cutaneum R57 and T. cutaneum ATCC 46490 yeast strains. The experiments implemented with microbial isolates obtained from three industrialized areas in Bulgaria showed that 7 of them may carry sequences hybridizing with a phenol hydroxylase oligonucleotide probe. A subsequent hybridization test for the cis,cis-muconate-lactonizing enzyme showed that only 3 of them displayed a positive signal. Lactobacillus acidophilus ATCC 4356 and Escherichia coli JM 109 strains' DNA used as negative controls in the experiments did not reveal any sequence similarity to the both applied oligonucleotides. The partial nucleotide sequences of 16S rDNAs of the isolated strains C1 and K1 obtained as PCR products were determined and sequenced. A comparison of these nucleotide sequences with similar sequences in NCBI Data Bank indicated that both C1 and K1 strains are closely related to the genera Acinetobacter and Burkholderia.