Cell Surface Energy Affects the Structure of Microalgal Biofilm.

Microalgae biofilm-based culture systems have wide applications in environmental engineering and biotechnology. Biofilm structure is critical for the transport of nutrients, gas, and signaling molecules in a microalgal biofilm. This work aims to understand the influence of cell surface energy (SE) on the microalgal biofilm structure. Three microalgae species were used as model cells in the study: Chlorella sp., Nannochloris oculata, and Chlorella pyrenoidosa. First, by mediating biofilm culture conditions, we obtained Chlorella sp. cells with SEs of 40.4 ± 1.5, 44.7 ± 1.0, and 62. 7 ± 1.2 mJ/m2, N. oculata cells with SEs of 47.7 ± 0.5, 41.1 ± 1.0, and 62.6 ± 1.2 mJ/m2, and C. pyrenoidosa cells with SEs of 64.0 ± 0.6, 62.1 ± 0.7, and 62.8 ± 0.6 mJ/m2. Then, based on the characterizations of biofilm structures, we found that cell SE can significantly affect the microalgae biofilm structure. When the cell SEs ranged from 40 to 50 mJ/m2, the microalgae cells formed heterogeneous biofilms with a large number of open voids, and the biofilm porosity was higher than 20%. Alternatively, when the cell SEs ranged from 50 to 65 mJ/m2, the cells formed a flat, homogeneous biofilm with the porosity lower than 20%. Finally, the influencing mechanism of cell SE on biofilm structure was interpreted based on the thermodynamic theory via analyzing the co-adhesion energy between cells. The study has important implications in understanding factors that influence the biofilm structures.

Further characterization of o-nitrobenzaldehyde degrading bacterium Pseudomonas sp: ONBA-17 and deduction on its metabolic pathway

A previously reported o-nitrobenzaldehyde (ONBA) degrading bacterium Pseudomonas sp. ONBA-17 was further identified and characterized. Based on results of DNA base composition and DNA-DNA hybridization, the strain was identified as P. putida. Its degradation effect enhanced with increase of inoculum amount and no lag phase was observed. Higher removal rate was achieved under shaking conditions. All tested ONBA with different initial concentrations could be completely degraded within 5 d. In addition, degradative enzyme(s) involved was confirmed as intra-cellular distributed and constitutively expressed. Effects of different compounds on relative activity of degradative enzyme(s) within cell-free extract were also evaluated. Finally, 2-nitrobenzoic acid and 2, 3-dihydroxybenzoic acid were detected as metabolites of ONBA degradation by P. putida ONBA-17, and relevant metabolic pathway was preliminary proposed. This study might help with future research in better understanding of nitroaromatics biodegradation.

Further characterization of o-nitrobenzaldehyde degrading bacterium Pseudomonas sp. ONBA-17 and deduction on its metabolic pathway.

A previously reported o-nitrobenzaldehyde (ONBA) degrading bacterium Pseudomonas sp. ONBA-17 was further identified and characterized. Based on results of DNA base composition and DNA-DNA hybridization, the strain was identified as P. putida. Its degradation effect enhanced with increase of inoculum amount and no lag phase was observed. Higher removal rate was achieved under shaking conditions. All tested ONBA with different initial concentrations could be completely degraded within 5 d. In addition, degradative enzyme(s) involved was confirmed as intra-cellular distributed and constitutively expressed. Effects of different compounds on relative activity of degradative enzyme(s) within cell-free extract were also evaluated. Finally, 2-nitrobenzoic acid and 2, 3-dihydroxybenzoic acid were detected as metabolites of ONBA degradation by P. putida ONBA-17, and relevant metabolic pathway was preliminary proposed. This study might help with future research in better understanding of nitroaromatics biodegradation.

Biotreatment of o-nitrobenzaldehyde manufacturing wastewater and changes in activated sludge flocs in a sequencing batch reactor.

o-Nitrobenzaldehyde manufacturing wastewater is characterized for being highly saline, with its TN content and dissolved organic concentrations giving rise to high COD loads. A sequencing batch reactor was established to investigate the effects of major processing variables, such as SRT and HRT, on system performance. The optimal COD (86%) and TN (40.9%) removal efficiencies were obtained at 16d (SRT) and 12 h (HRT). Design equations were developed by applying experimental data. Changes in sludge flocs were studied using a combination of methods including: chemical analysis; fluorescence in situ hybridization (FISH); and denaturing gradient gel electrophoresis profile analysis of 16S rRNA genes. Dramatic changes occurred during adaptation and ß-Proteobacteria was found to be the most prevalent population. Besides, some species affiliated with α-subclasses of Proteobacteria and Cytophaga-Flavobacterium-Bacteroides (CFB) group were also enriched. This study may help with future research in providing a better understanding of the activated sludge biotreatment.

Bioaugmentation of a sequencing batch reactor with Pseudomonas putida ONBA-17, and its impact on reactor bacterial communities.

This study demonstrates the feasibility of using Pseudomonas putida ONBA-17 to bioaugment a sequencing batch reactor (SBR) treating o-nitrobenzaldehyde (ONBA) synthetic wastewater. To monitor its survival, the strain was chromosomally marked with gfp gene. After a transient adaptation, almost 100% degradation of ONBA was obtained within 8 days as compared with 23.47% of the non-inoculated control. The bioaugmented reactor has a better chemical oxygen demand (COD) removal performance (96.28%) than that (79.26%) of the control. The bioaugmentation not only enhanced the removal capability of target compound, but shortened system start-up time. After the increase in ONBA load, performance fluctuation of two reactors was observed, and the final treating effects of them were comparable. What is more, denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes via a combination of pattern comparison and sequence phylogenetic analysis was performed to uncover changes in sludge microbial communities. Only the members of alpha, beta and gamma subdivisions of Proteobacteria were identified. To isolate ONBA-degrading relevant microorganisms, spread plate was used and four bacterial strains were obtained. Subsequent systematic studies on these bacteria characterized their traits which to some extent explained why such bacteria could be kept in the system. This study will help future research in better understanding of the bioreactor bioaugmentation.