Rapid quantification and analysis of genetic diversity among Gordonia populations in foaming activated sludge plants

Recent advances in understanding the ecology of the filamentous bacteria responsible for activated sludge bulking

Activated sludge bulking caused by filamentous bacteria is still a problem in wastewater treatment plants around the world. Bulking is a microbiological problem, and so its solution on species-specific basis is likely to be reached only after their ecology, physiology and metabolism is better understood. Culture-independent molecular methods have provided much useful information about this group of organisms, and in this review, the methods employed and the information they provide are critically assessed. Their application to understanding bulking caused by the most frequently seen filament in Japan, 'Ca. Kouleothrix', is used here as an example of how these techniques might be used to develop control strategies. Whole genome sequences are now available for some of filamentous bacteria responsible for bulking, and so it is possible to understand why these filaments might thrive in activated sludge plants, and provide clues as to how eventually they might be controlled specifically.

Disentangling Community Structure of Ecological System in Activated Sludge: Core Communities, Functionality, and Functional Redundancy

The microbial ecosystems of the sludge were characterized in terms of the core community structure, functional pathways, and functional redundancy through Illumina MiSeq sequencing and PICRUSt analysis on the activated sludge (AS) samples from an extended activated aeration process. Based on the identified OTU distribution, we identified 125 core community genera, including 3 abundant core genera and 21 intermittent abundant core genera. Putative genera Nitrosomonas, Nitrotoga, Zoogloea, Novosphingobium, Thermomonas, Amaricoccus, Tetrasphaera, Candidatus Microthrix, and Haliscomenobacter, which are associated with functions of nitrifying, denitrifying, phosphorus accumulating, and bulking and foaming, were found to present as the core community organisms in the AS sampled from the conventional extended aeration AS processes. The high-abundant nitrogen metabolic pathways were associated with nitrate reduction to ammonium (DNRA and ANRA), denitrification, and nitrogen fixation, while the ammonia oxidation-related genes (amo) were rarely annotated in the AS samples. Strict functional redundancy was not found with the AS ecosystem as it showed a high correlation between the community composition similarity and function similarity. In addition, the classified dominant core genera community was found to be sufficient to characterize the functionality of AS, which could invigorate applications of 16S rDNA MiSeq sequencing and PICRUSt for the prediction of functions of AS ecosystems.

The ratio of metabolically active versus total Mycolata populations triggers foaming in a membrane bioreactor

The abundance of total and metabolically active populations of Mycolata was evaluated in a full-scale membrane bioreactor (MBR) experiencing seasonal foaming, using quantitative PCR (qPCR) and retrotranscribed qPCR (RT-qPCR) targeting the 16S rRNA gene sequence. While the abundance of total Mycolata remained stable (10(10) copies of 16S rRNA genes/L activated sludge) throughout four different experimental phases, significant variations (up to one order of magnitude) were observed when the 16S rRNA was targeted. The highest ratios of metabolically active versus total Mycolata populations were observed in samples of two experimental phases when foaming was experienced in the MBR. Non-metric multidimensional scaling and BIO-ENV analyses demonstrated that this ratio was positively correlated to the concentrations of substrates in the influent water, F/M ratio, and pH, and negatively correlated to temperature and solids retention time. It the first time that the ratio of metabolically active versus total Mycolata is found to be a key parameter triggering foaming in the MBR; thus, we propose it as a candidate predictive tool.

Interlinkages between bacterial populations dynamics and the operational parameters in a moving bed membrane bioreactor treating urban sewage

Bacteria are key players in biological wastewater treatments (WWTs), thus a firm knowledge of the bacterial population dynamics is crucial to understand environmental/operational factors affecting the efficiency and stability of the biological depuration process. Unfortunately, little is known about the microbial ecology of the advanced biological WWTs combining suspended biomass (SB) and attached biofilms (AB). This study explored in depth the bacterial community structure and population dynamics in each biomass fraction from a pilot-scale moving bed membrane bioreactor (MBMBR) treating municipal sewage, by means of temperature-gradient gel electrophoresis (TGGE) and 454-pyrosequencing. Eight experimental phases were conducted, combining different carrier filling ratios, hydraulic retention times and concentrations of mixed liquor total suspended solids. The bacterial community, dominated by Proteobacteria (20.9-53.8%) and Actinobacteria (20.6-57.6%), was very similar in both biomass fractions and able to maintain its functional stability under all the operating conditions, ensuring a successful and steady depuration process. Multivariate statistical analysis demonstrated that solids concentration, carrier filling ratio, temperature and organic matter concentration in the influent were the significant factors explaining population dynamics. Bacterial diversity increased as carrier filling ratio increased (from 20% to 35%, v/v), and solids concentration was the main factor triggering the shifts of the community structure. These findings provide new insights on the influence of operational parameters on the biology of the innovative MBMBRs.

Development and evaluation of a TaqMan duplex real-time PCR quantification method for reliable enumeration of Candidatus Microthrix

Candidatus Microtrhix parvicella is one of the most common filamentous bacteria reported to be involved in bulking and foaming problems in activated sludge plants worldwide. In order to detect and quantify both M. parvicella and Microthrix calida by quantitative PCR (qPCR), primers targeting 16S rDNA genes were designed. The qPCR reaction was optimized by using the TaqMan technology and an internal positive control was included to ensure the absence of PCR inhibitors. A total of 29 samples originating from different wastewater treatment plants were analyzed and the results were compared by using conventional microscopy, fluorescent in situ hybridization and an existing SYBR Green-based assay. Our assay showed a 100% specificity for both M. parvicella and M. calida, a sensitivity of 2.93×10(9) to 29 copy numbers/reaction, an amplification efficiency of 93% and no PCR inhibition. By performing a spiking experiment including different Microthrix concentrations, recovery rates ranging from 65 to 98% were obtained. A positive correlation with the SYBR Green assay (R(2)=0.85) was found and most of the samples were in accordance with the microscopical observation. In comparison with SYBR Green assay, the probe-based TaqMan assay had a much lower detection limit. Compared with microscopy, some samples had a lower or higher enumeration when using qPCR. In conclusion, a qPCR method is forwarded here that could be useful as an early warning tool for fast and reliable detection of Microthrix in for instance sludge bulking events.