Antimony toxicity upon microorganisms from aerobic and anaerobic environments.

Antimony (Sb) is a toxic and carcinogenic metalloid that can be present in contaminated water generated by mining operations and other industrial activities. The toxicity of Sb (III) and Sb (V) to aerobic microorganisms remains limited and unexplored for anaerobic microorganisms involved in hydrogen (H2) and methane (CH4) production. This study aimed to evaluate the toxicity of Sb (III) and Sb (V) upon aerobic and anaerobic microorganisms important in biological wastewater treatment systems. Sb (III) was more toxic than Sb (V) independently of the test and environment evaluated. Under aerobic conditions maintained in the Microtox assay, Sb (V) was not toxic to Allivibrio fischeri at concentrations as high as 500 mg/L, whereas Sb (III) caused just over 50% inhibition at concentration of 250 mg/L after 5 min of exposure. In the respirometry test, for the specific oxygen uptake rate, the concentrations of Sb (III) and Sb (V) displaying 50% inhibition were 0.09 and 56.2 mg/L, respectively. Under anaerobic conditions, exposure to Sb (III) and Sb (V) led to a decrease in microorganisms activity of fermentative and methanogenic processes. The results confirm that the microbial toxicity of Sb depends on its speciation and Sb (III) displays a significantly higher inhibitory potential than Sb (V) in both aerobic and anaerobic environments.

Evaluation of inhibitory compounds produced by bacteria isolated from a hydrogen-producing bioreactor during the self-fermentation of wheat straw.

AIMS: The objective of this study was to evaluate the inhibitory activity of compounds secreted by bacteria isolated from a hydrogen-producing bioreactor to understand how these microorganisms interact in this community. METHODS AND RESULTS: In vitro inhibitory assays were performed using samples secreted by bacteria subject to different treatments to determine if their inhibitory effect was due to organic acids, non-proteinaceous compounds or bacteriocin-like inhibitory substances (BLIS). Bacterial isolated were suppressed 43%, 30% and 27% by neutralized, precipitated and non-neutralized cell-free supernatants, respectively. Non-hydrogen producers (non-H2 P) lactic acid bacteria (LAB) (Lactobacillus plantarum LB1, Lactobacillus pentosus LB7, Pediococcus acidilactici LB4) and hydrogen producers (H2 P) LAB (Enterococcus faecium F) were inhibited by the production of organic acids, non-proteinaceous compounds and BLIS. Meanwhile, the obligate anaerobe H2 P (Clostridium beijerinckii B) inhibited by the production of non-proteinaceous compounds and BLIS. The presence of BLIS was confirmed when proteolytic enzymes affected the inhibitory activity of secreted proteins in values ranging from 20% to 42%. The BLIS produced by L. plantarum LB1, P. acidilactici LB4, L. pentosus LB7 and E. faecium F showed molecular masses of ~11, 25, 20 and 11 kDa, respectively. CONCLUSIONS: It was demonstrated antagonistic interactions between Lactobacillus-Enterococcus and Pediococcus-Enterococcus species, generated by the secretion of organic acids, non-proteinaceous compounds and BLIS. SIGNIFICANCE AND IMPACT OF THE STUDY: We report the interactions between LAB isolated from hydrogen-producing bioreactors. These interactions might impact the dynamics of the microbial population during hydrogen generation. Our work lays a foundation for strategies that allow controlling bacteria that can affect hydrogen production.

The duo Clostridium and Lactobacillus linked to hydrogen production from a lignocellulosic substrate.

The study aimed to identify interspecies interactions within a native microbial community present in a hydrogen-producing bioreactor fed with two wheat straw cultivars. The relationships between the microbial community members were studied building a canonical correspondence analysis and corroborated through in vitro assays. The results showed that the bioreactor reached a stable hydrogen production of ca. 86 mL/kg·d in which the cultivar change did not affect the average performance. Lactobacillus and Clostridium dominated throughout the whole operation period where butyric acid was the main metabolite. A canonical correspondence analysis correlated positively Lactobacillus with hydrogen productivity and hydrogen-producing bacteria like Clostridium and Ruminococaceae. Agar diffusion testing of isolated strains confirmed that Lactobacillus inhibited the growth of Enterococcus, but not of Clostridium. We suggest that the positive interaction between Lactobacillus and Clostridium is generated by a division of labor for degrading the lignocellulosic substrate in which Lactobacillus produces lactic acid from the sugar fermentation while Clostridium quickly uses this lactic acid to produce hydrogen and butyric acid. The significance of this work lies in the fact that different methodological approaches confirm a positive association in the duo Lactobacillus-Clostridium in a bioreactor with stable hydrogen production from a complex substrate.

Simultaneous hydrogen production and decolorization of denim textile wastewater: kinetics of decolorizing of indigo dye by bacterial and fungal strains.

This study proposes the treatment and valorization of denim textile effluents through a fermentative hydrogen production process. Also, the study presents the decolorizing capabilities of bacterial and fungal isolates obtained from the fermented textile effluents. The maximum hydrogen production rate was 0.23 L H2/L-d, achieving at the same time color removal. A total of thirty-five bacteria and one fungal isolate were obtained from the fermented effluents and screened for their abilities to decolorize indigo dye, used as a model molecule. From them, isolates identified as Bacillus BT5, Bacillus BT9, Lactobacillus BT20, Lysinibacillus BT32, and Aspergillus H1T showed notable decolorizing capacities. Lactobacillus BT20 reached 90% of decolorization using glucose as co-substrate after 11 days of incubation producing colorless metabolites. Bacillus BT9 was able to utilize the indigo dye as the sole carbon source achieving a maximum decolorization of 60% after 9 days of incubation and producing a red-colored metabolite. In contrast, Bacillus BT5 and Lysinibacillus BT32 exhibited the lowest percentages of decolorization, barely 33% after 16 and 11 days of incubation, respectively. When Aspergillus H1T was grown in indigo dye supplemented with glucose, 96% of decolorization was reached after 2 days. This study demonstrates the valorization of denim textile effluents for the production of hydrogen via dark fermentation with concomitant color removal.