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The predation of Bdellovibrio bacteriovorus on different periodontal pathogens has already been described. However, it is necessary to consider the polymicrobial nature of periodontal disease. The current study explores the predation of Bdellovibrio on oral pathogens organized in multispecies communities. The effect of the predator was evaluated on in vitro six species communities with microbial culturing. Additionally, the effect on ex vivo subgingival plaque and saliva samples from periodontitis patients was assessed. In the latter experiment results were examined with microbial culturing, quantitative polymerase chain reaction (qPCR) and denaturing gradient gel electrophoresis (DGGE). The latter technique was used to get an overview of the whole mixed microbial population. Results showed that even in more complex models, B. bacteriovorus was still able to predate on Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans . However predation on Prevotella intermedia and Porphyromonas gingivalis could not be validated in multispecies models. The effect of Bdellovibrio was not restricted to the target bacteria. Changes in the overall ecology of the different models were evident. It could be concluded that the efficiency of predation decreased when complexity of the models increased. However, B. bacteriovorus was able to attack two important oral pathogens, F. nucleatum, and A. actinomycetemcomitans, even when present in ex vivo clinical samples. These effects still have to be validated in in vivo models to see the impact of Bdellovibrio on the whole bacterial ecology. [ABSTRACT FROM AUTHOR]

The removal of volatile organic compounds (VOCs) in air is of utmost importance to safeguard both environmental quality and human well-being. However, the low aqueous solubility of hydrophobic VOCs results in poor removal in waste gas biofilters (BFs). In this study, we evaluated the addition of (bio)surfactants in three BFs (BF1 and BF2 mixture of compost and wood chips (C + WC), and BF3 filled with expanded perlite) to enhance the removal of cyclohexane and hexane from a polluted gas stream. Experiments were carried out to select two (bio)surfactants (i.e., Tween 80 and saponin) out of five (sodium dodecyl sulfate (SDS), Tween 80, surfactin, rhamnolipid and saponin) from a physical-chemical (i.e., decreasing VOC gas-liquid partitioning) and biological (i.e., the ability of the microbial consortium to grow on the (bio)surfactants) point of view. The results show that adding Tween 80 at 1 critical micelle concentration (CMC) had a slight positive effect on the removal of both VOCs, in BF1 (e.g., 7.0 ± 0.6 g cyclohexane m−3 h−1, 85 ± 2% at 163 s; compared to 6.7 ± 0.4 g cyclohexane m−3 h−1, 76 ± 2% at 163 s and 0 CMC) and BF2 (e.g., 4.3 ± 0.4 g hexane m−3 h−1, 27 ± 2% at 82 s; compared to 3.1 ± 0.7 g hexane m−3 h−1, 16 ± 4% at 82 s and 0 CMC), but a negative effect in BF3 at either 1, 3 and 9 CMC (e.g., 2.4 ± 0.4 g hexane m−3 h−1, 30 ± 4% at 163 s and 1 CMC; compared to 4.6 ± 1.0 g hexane m−3 h−1, 43 ± 8% at 163 s and 0 CMC). In contrast, the performance of all BFs improved with the addition of saponin, particularly at 3 CMC. Notably, in BF3, the elimination capacity (EC) and removal efficiency (RE) doubled for both VOCs (i.e., 9.1 ± 0.6 g cyclohexane m−3 h−1, 49 ± 3%; 4.3 ± 0.3 g hexane m−3 h−1, 25 ± 3%) compared to no biosurfactant addition (i.e., 4.5 ± 0.4 g cyclohexane m−3 h−1, 23 ± 3%; hexane 2.2 ± 0.5 g m−3 h−1, 10 ± 2%) at 82 s. Moreover, the addition of the (bio)surfactants led to a shift in the microbial consortia, with a different response in BF1–BF2 compared to BF3. This study evaluates for the first time the use of saponin in BFs, it demonstrates that cyclohexane and hexane RE can be improved by (bio)surfactant addition, and it provides recommendations for future studies in this field. [Display omitted] • The effect of surfactant addition in 3 BFs treating hydrophobic VOCs was evaluated. • The selection of appropriate (bio)surfactant type and concentration showed to be critical. • A positive effect in all BFs was observed when saponin was added at 3 CMC. • The addition of (bio)surfactants led to a shift in the microbial consortia. • The results show the interplay of different physical-chemical and biological processes. [ABSTRACT FROM AUTHOR]

Kitchen waste and molasses are organic waste streams with high organic content, and therefore are interesting substrates for renewable energy production by means of anaerobic digestion. Both substrates, however, often cause inhibition of the anaerobic digestion process, when treated separately, hence, co-digestion with other substrates is required to ensure stable methane production. In this research, A-sludge (sludge harvested from a high rate activated sludge system) was used to stabilize co-digestion with kitchen waste or molasses. Lab-scale digesters were fed with A-sludge and kitchen waste or molasses for a total period of 105 days. Increased methane production values revealed a stabilizing effect of concentrated A-sludge on kitchen waste digestion. Co-digestion of molasses with A-sludge also resulted in a higher methane production. Volumetric methane production rates up to 1.53 L L −1 d −1 for kitchen waste and 1.01 L L −1 d −1 for molasses were obtained by co-digestion with A-sludge. The stabilizing effect of A-sludge was attributed to its capacity to supplement various nutrients. Microbial community results demonstrated that both reactor conditions and substrate composition determined the nature of the bacterial community, although there was no direct influence of micro-organisms in the substrate itself, while the methanogenic community profile remained constant as long as optimal conditions were maintained. [ABSTRACT FROM AUTHOR]

The production of shrimp is often performed in earthen outdoor ponds in which the high input of feed and faeces on the bottom can result in deterioration of the water quality, which negatively impacts the animals and the environment. Here, we investigate the potential of sodium molybdate (Na₂MoO₄·2H₂O), sodium nitrate (NaNO 3) and sodium percarbonate (Na 2 CO 3 ·1.5H 2 O 2) to control sulphide production in a simulated shrimp pond bottom system that included the sediment, overlaying artificial seawater and organic matter input in the form of shrimp feed and shrimp faeces. Sediment depth gradient measurements of oxygen, H 2 S and pH were obtained during 7 days of incubation using microelectrodes. The most significant impact in terms of H 2 S, was observed for 50 mg/L sodium molybdate. At the water-sediment interface, there was up to 73% less H 2 S detected for this treatment in comparison to a control treatment, while in the deeper layers of the sediment it was up to 47% less H 2 S. The residual sulphate concentrations in the molybdate treated samples were 16 ± 4% higher than the control, indicating an inhibition in sulphate reduction. Nitrate and sodium percarbonate treatments also showed a limited capacity to decrease H 2 S entering in the water column, yet no clear difference in H 2 S concentrations in the sediment compared to the control were observed. Molybdate treatment appears to work through the inhibition of sulphate reducing bacteria in situ for the control of H 2 S production better than the chemical oxygen boosters or nitrate treatment. • An experimental shrimp pond model was used to evaluate target specific strategies. •Molybdate treatment reduced H 2 S production in a simulated shrimp pond bottom. •Sulphate reducing bacteria activity was partially inhibited by molybdate. •Molybdate works better than oxygen booster compounds to control H 2 S production. [ABSTRACT FROM AUTHOR]

Abstract: Syrup formation in refrigerated doughs is a problem since it reduces the doughs’ shelf life. Microbial exogenous xylanases associated with wheat kernels were found to play a role in this syruping phenomenon. Using xylanase-producing microorganisms isolated from wheat kernels, we investigated their potency to induce syruping in dough. Growth of the fungal xylanase producer Fusarium sp. (102 colony forming units (CFU)/g dough) and the bacterial xylanase producer Paenibacillus sp. (104 CFU/g dough) in synthetic media and their respective addition to wheat dough could not bring about a significant amount of syruping. However, when these species were grown on moist wheat kernels and an extract of these kernels containing both the organisms and its xylanases was made and added to dough, intensive syruping was noted. This effect was primarily attributed to the xylanases present in the extract. These findings suggest that the involvement of xylanase-producing microorganisms in the syruping phenomenon is situated prior to harvest. Additional quantitative analyses of microbial biomass present on wheat kernels revealed that the fungi in particular could be correlated to higher microbial exogenous xylanase activities on wheat. Our results indicate that the syruping is linked to fungal xylanase production on the wheat kernels in the field. [Copyright &y& Elsevier]