Biological nitrogen removal and metabolic characteristics of a novel cold-resistant heterotrophic nitrification and aerobic denitrification Rhizobium sp. WS7.

For improving the poor de-nitrogen efficiency and effluent quality faced by wastewater treatment plants in winter, a novel cold-resistant strain, Rhizobium sp. WS7 was isolated. Strain WS7 presented dramatic de-nitrogen efficiencies including 98.73 % of NH4+-N, 99.98 % of NO3--N, 100 % of NO2--N and approximately 100 % of mixed nitrogen (NH4+-N and NO3--N) at 15 °C. Optimum parameters of WS7 for aerobic denitrification were determined. Additionally, functional genes (amoA, napA, nirK, norB, and nosZ) and key enzymes (nitrate reductase and nitrite reductase) activities were determined. Nitrogen balance analysis suggested that assimilation played a dominant role in de-nitrogen by WS7, the NH4+-N metabolic pathway was deduced as NH4+-N â†’ NH2OH â†’ NO â†’ N2O â†’ N2, and the NO3--N/NO2--N metabolic pathway was deduced as NO3--N â†’ NO2--N â†’ NO â†’ N2O â†’ N2. The cold-resistant Rhizobium sp. WS7 has great application feasibility in cold sewage treatment.

Diversity of culturable aerobic denitrifying bacteria in the sediment, water and biofilms in Liangshui River of Beijing, China.

Aerobic denitrification is a process reducing the nitrate into gaseous nitrogen forms in the presence of oxygen gas, which makes the nitrification and denitrification performed simultaneously. However, little was known on the diversity of the culturable aerobic denitrifying bacteria in the surface water system. In this study, 116 strains of aerobic denitrifying bacteria were isolated from the sediment, water and biofilm samples in Liangshui River of Beijing. These bacteria were classified into 14 genera based on the 16 S rDNA, such as Pseudomonas, Rheinheimera, and Gemmobacter. The Pseudomonas sp., represented by the Pseudomonas stutzeri, Pseudomonas mendocina and Pseudomonas putida, composed the major culturable aerobic denitrifiers of the river, followed by Ochrobactrum sp. and Rheinheimera sp. The PCA plot showed the unclassified Pseudomonas sp. and Rheinheimera pacifica preferred to inhabit in biofilm phase while one unclassified Ochrobactrum sp. and Pseudomonas resinovorans had higher abundance in the sediment. In the overlying water, the Pseudomonas stutzeri and Ochrobactrum rhizosphaerae were found to have higher abundance, indicating these aerobic denitrifiers had different habitat-preferable characteristics among the 3 phases of river system. The findings may help select the niche to isolate the aerobic denitrifiers and facilitate the bioaugmentation-based purification of the nitrate polluted surface water.

Succession of biofilm communities responsible for biofouling of membrane bio-reactors (MBRs).

Biofilm formation is one of the main factors associated with membrane biofouling in membrane bioreactors (MBRs). As such, it is important to identify the responsible organisms to develop targeted strategies to control biofouling. This study investigated the composition and changes in the microbial communities fouling MBR membranes over time and correlated those changes with an increase in transmembrane pressure (TMP). Based on qPCR data, bacteria were the dominant taxa of the biofilm (92.9-98.4%) relative to fungi (1.5-6.9%) and archaea (0.03-0.07%). NMDS analysis indicated that during the initial stages of operation, the biofilm communities were indistinguishable from those found in the sludge. However, the biofilm community significantly diverged from the sludge over time and ultimately showed a unique biofilm profile. This suggested that there was strong selection for a group of organisms that were biofilm specialists. This pattern of succession and selection was correlated with the rapid increase in TMP, where bacteria including Rhodospirillales, Sphingomonadales and Rhizobiales dominated the biofilm at this time. While most of the identified fungal OTUs matched Candida sp., the majority of fungal communities were unclassified by 18S rRNA gene sequencing. Collectively, the data suggests that bacteria, primarily, along with fungi may play an important role in the rapid TMP increase and loss of system performance.