Understanding of signaling molecule controlled anammox through regulating C/N ratio

Rhizobial, passenger nodule endophytes and phyllosphere bacteria in combination with acyl homoserine lactones enhances the growth and yield of groundnut

Quorum sensing (QS) mechanisms play an essential role in mediating several signals and plant-bacteria interactions, promoting plant growth. This study demonstrated production of multiple Homoserine lactone (HSL) molecules like C6 HSL, C7 HSL, C8 HSL, 3-Hydroxy-C8-HSL and 3-oxo-C14 HSL in rhizobial and passenger endophytes and phyllospheric bacteria which regulated production of plant growth promoting traits viz., indole acetic acid and exo-polysaccharide production, biofilm formation, and motility. Quorum quenching (QQ) molecules like salicylic acid, gallic acid, and disalicylic acid impaired these traits, but exogenous addition of QS molecules (C7HSL and 3-oxo-C14 HSL) restored these inhibitory effects of QQ compounds. The pot culture experiment revealed that the treatment involving Methylobacterium populi TMV7-4 or Enterobacter cloacae S23 with salicylic acid, C7HSL and 3-oxo-C14 HSL significantly enhanced plant growth including root length, nodulation, pod formation, soil available nutrients and plant nutrients uptake. In future field validation is required for the use of QS molecules in improving groundnut production.

Increasing carbon to nitrogen ratio promoted anaerobic ammonia-oxidizing bacterial enrichment and advanced nitrogen removal in mainstream anammox system

The effects of fluctuating organic carbon to nitrogen (C/N) ratios on mainstream simultaneous partial nitrification, anammox, and denitrification (SNAD) process were studied over 376-day period. The nitrogen removal efficiency decreased from 85.0 ± 6.6 % to 75.8 ± 2.8 % as C/N ratio decreased (3.4 → 1.7), but increased to 82.0 ± 1.9 % when C/N ratio raised to 2.9 and to 78.4 ± 3.0 % when C/N ratio decreased again (2.9 → 2.1), indicating that high C/N ratios promoted nitrogen removal. As C/N ratio raised (1.7 → 2.9), anaerobic ammonia-oxidizing bacteria (AnAOB) abundance increased from 1.3 × 109 to 2.0 × 109 copies/L, which explained the improved nitrogen removal. With an elevated C/N ratio, partial nitrification and endogenous partial denitrification reactions were enhanced, providing more nitrite for AnAOB. Additionally, the aerobic_chemoheterotrophy function and particle sizes increased, forming more stable anoxic microenvironment for AnAOB. Overall, increasing C/N ratio promoted the stability of mainstream SNAD.

Antibiotics resistance removal from piggery wastewater by an integrated anaerobic-aerobic biofilm reactor: Efficiency and mechanism

Antibiotic resistance residual in piggery wastewater poses serious threat to environment and human health. Biological treatment process is commonly installed to remove nutrient from piggery wastewater and also effective in removing antibiotics to varying degrees. But the specific pathways and mechanisms involved in the removal of antibiotic resistance are not yet well-understood. An integrated anaerobic-aerobic biofilm reactor (IAOBR) has been demonstrated efficient in removing conventional nutrients. It is here shown that the IAOBR effectively removed 79.0% of Sulfonamides, 55.7% of Tetracyclines and 53.6% of Quinones. Antibiotic resistance bacteria (ARB) were simultaneously inactivated by ~0.5 logs. Antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) were decreased by 0.51 logs and 0.42 logs, respectively. The antibiotics were mainly removed through aerobic compartments of the IAOBR. The mass loss of antibiotics in the reactor was achieved by biodegradation and adsorption, accounting for 52.1% and 47.9%, respectively. An obvious accumulation of ARGs was observed in the activated sludge. The potential host of ARGs was analyzed via microbial community and network. Partial least squares-structural equation model and correlation analysis revealed that the enrichment of ARGs was positively affected by MGEs, followed by bacterial community and ARBs, but the effect of antibiotics on ARGs was negative. Outcomes of this study provide valuable insights into the mechanisms of antibiotic resistance removal in biological treatment processes.

Impacts of exogenous quorum sensing signal molecule-acylated homoserine lactones (AHLs) with different addition modes on Anammox process

Anammox was proved having the quorum sensing ability, and several acylated homoserine lactones (AHLs) signal molecules were detected in the system. In this study, the impact of exogenous N-dodecanoyl homoserine lactone (C12-HSL) with different addition modes on the nitrogen removal, key enzymes' activity, and microbial revolution were investigated in Anammox system. Results showed that once-addition of C12-HSL had no obvious impact on Anammox. Daily-addition with 40 nM slightly improved the TN removal from 71.1 % to 74.5 %, while 80 and 200 nM significantly decreased it to 62.7 % and 61.8 %, respectively. The enzyme activity of ammonia monooxygenase increased from 0.015 to 0.068, nitrite reductase increased from 0.25 to 1.23, and nitrate reductase increased from 0.05 to 0.11 μg NO₂^--N mg^-1 Protein min^-1. Arenimonas abundance showed positive correlation with TN removal while Candidatus Kuenenia was continuously suppressed. C12-HSL was beneficial for partial nitrification, and it could be adopted for regulating the nitrite production.

Regulating performance of CANON process via adding external quorum sensing signal molecules in membrane bioreactor

In this study, the regulation effect of the external quorum sensing signals, N-dodecanoyl homoserine lactone (C12-HSL) on CANON process were investigated in a membrane bioreactor. C12-HSL significantly enhanced the aerobic ammonia-oxidizing bacteria and improved the ammonia monooxygenase activity to 0.134 from 0.076 μg NO₂^--N mg^-1 protein min^-1, while suppressed anaerobic ammonia-oxidizing bacteria and limited the TN removal to 0.07 from 0.22 kg m^-3 d^-1. Key enzymes synthesis were enhanced during the operation without C12-HSL addition, enabling the resistance of CANON system to high C12-HSL. As a result, the hydroxylamine oxidoreductase and nitrite reductase activity reached 35.9 EU g^-1 SS and 1.28 μg NO₂^--N mg^-1 protein min^-1, respectively; Nitrosomonas and Candidatus Kuenenia, with the abundance as 12.5 % and 22.9 %, cooperatively contributed to the TN removal, which maintained at 0.19 kg m^-3 d^-1. C12-HSL was profitable for aerobic ammonia oxidation, which could be adopted for regulating the nitrite production rate.

Using an innovative umbrella-shape membrane module to improve MBR for PN-ANAMMOX process

Membrane fouling has been a key factor limiting the applications of membrane bioreactor (MBR). In this study, a novel umbrella-shape membrane module was applied to construct two MBRs for two-stage partial nitrification-anaerobic ammonia oxidation (PN-ANAMMOX) process. After 55 days operation, the ANAMMOX process was started and the PN process was well controlled. Then, the ANAMMOX and PN process were successfully coupled to run the PN-ANAMMOX process. On 103 days, the best nitrogen removing effect was achieved with the maximum nitrogen loading rate (NLR) of 0.4 kg N·(m³·d)^-1 and the corresponding maximum total nitrogen removal rate (TNRR) of 75.23%. The umbrella-shape membrane module in both reactors only needed to be cleaned once during the operation for 105 days, indicating that the membrane module had better resistance to membrane fouling. The functional bacteria were cultivated in suspension state; moreover, the cell densities of ammonia oxidizing bacteria (AOB) and ANAMMOX bacteria (AnAOB) reached 58.32 × 10¹² copies/g sludge and 28.39 × 10¹² copies/g sludge. Their abundances reached 73.25% and 57.80% of the total bacteria, respectively. MBR improved by umbrella-shape membrane module could realize the rapid start-up of ANAMMOX process, effective control of PN process, and stable operation of PN-ANAMMOX process. This study provided a novel approach to control membrane fouling by optimizing the membrane module shape and widened applications of MBRs in PN-ANAMMOX process.

Activation of N-acyl-homoserine lactone-mediated quorum sensing system improves long-term preservation of anammox microorganisms by vacuum lyophilization

The long-term preservation of anaerobic ammonium oxidation (anammox) microorganisms via vacuum lyophilization process would help commercialize the technique. In this study, vacuum lyophilization was evaluated for the cost-effective long-term preservation of such microorganisms. Skim milk was found to be the most effective cryoprotectant for maintaining the physiological properties (heme c, EPS, and the PN/PS ratio) of anammox microorganisms. Conversely, the vacuum lyophilization technique was shown to cause serious damage to the quorum sensing (QS) system of anammox, so that anammox activity was not adequately recovered afterwards. To overcome this limitation, activation of the AHL-mediated QS system were applied to the vacuum lyophilization process. Endogenous (i.e., fresh anammox sludge of 10%) and exogenous (i.e., C6-HSL of 60 mg/L) QS autoinducers significantly increased anammox activity to 88.2 ± 12.2 and 130.0 ± 12.2 mgTN/gVSS/d, respectively, after 56 d of reactivation. In addition, nitrogen removal potentials were estimated to be 123.5 and 87.5 gTN/m³/d, respectively. The effect of the exogenous QS autoinducer on anammox reactivation was reconfirmed through the comparison experiment. The results of this study will be greatly significant to this field since they improve the feasibility of the once-underestimated vacuum lyophilization technique.

Insight into the effect of N-acyl-homoserine lactones-mediated quorum sensing on the microbial social behaviors in a UASB with the regulation of alkalinity

N-acyl-homoserine lactones (AHLs)-mediated quorum sensing (QS) has been reported as the inducers of microbial social behaviors in anaerobic digestion (AD) processes. However, it is not well understood that how to intentionally change the secretion of AHLs by conventional engineering control such as the regulation of alkalinity. The present research investigated the effect of endogenous AHLs-mediated QS on the microbial social behaviors in an upflow anaerobic sludge bed (UASB) reactor with the influent alkalinity decreased from 2800 mg/L to 700 mg/L by stages. The results showed that the alkalinity of 1800-2200 mg/L was more favorable for the AD in the UASB, with an excellent specific methanogenic activity (SMA) and better microbial aggregation statuses. The alkalinity out of the favorable alkalinity range would decrease the SMA with the accumulation of VFAs in the reactor. It was found that signal molecule C₄-HSL was always the dominant AHL in the UASB along with the decrease of influent alkalinity, while 3-oxo-C₆-HSL, 3-oxo-C₁₂-HSL and C₁₄-HSL were remarkably improved only within the favorable range of alkalinity. Pearson correlation concluded that the dominant signal molecule C₄-HSL was the specific AHL in enhancing the synthesis of extracellular polysaccharide and the metabolism of acidogens. The co-occurrence network revealed that Mesotoga, Sulfurospirillum and Methanoregula were the key hubs in the microbial interaction network, and the AHLs-mediated QS indirectly facilitated the methanogenic metabolism. The present work provided a revealing insight into the effect of AHLs-mediated QS on the microbial social behaviors in AD process with the regulation of alkalinity.