Elucidating the mechanisms associated with the anaerobic biotransformation of the emerging contaminant nitroguanidine

Research on bioaugmented slurry remediation of PAHs in actual contaminated soil: Screening microbial agents and optimizing key parameters

Bioaugmented slurry technology is a sustainable remediation technology for PAHs-contaminated soil. However, the lack of experimental data on the remediation of complex, actual contaminated soils has hindered the practical application of this technology. This study explored the bioaugmented degradation of PAHs using actual soil slurry with and without the addition of microbial agents in the microscopic world. NS4 has the highest degradation efficiency. The response surface method was used to determine the effects of water-soil ratio, temperature, aeration rate and their interaction on the degradation of PAHs. Temperature significantly affects the degradation of phenanthrene, and the aeration rate significantly affects the degradation of pyrene. The influence of each factor follows the order: aeration rate > temperature > water-soil ratio. The highest degradation rates of phenanthrene and pyrene are observed at a water-soil ratio of 3:1, a temperature of 30 °C, and an aeration rate of 2 L/min. Under the optimal conditions, the addition of either peptone or Tween-80 increased the degradation rate. Peptone and Tween-80 can effectively enhance the growth rate of microorganisms and the release of PAHs in actual contaminated soil. In conclusion, by screening microbial agents suitable for real contaminated soils and maintaining the dynamic stability of the bioaugmented slurry system by optimizing key influencing factors, efficient, green, and low-energy remediation of PAHs-contaminated sites can be achieved.

Genome-centric metagenomic analysis reveals mechanisms of quorum sensing promoting anaerobic digestion under sulfide stress: Syntrophic metabolism and microbial self-adaptation

Sulfide stress is a common inhibition factor in anaerobic digestion systems with sulfur-rich feedstocks. Quorum sensing (QS) signaling molecule N-acyl-homoserine lactones (AHLs) possess positive effect on promoting anaerobic digestion. However, the micro-biological mechanisms of AHLs affecting syntrophic metabolism and microbial self-adaptation have not yet been deciphered in anaerobic digestion under sulfide stress. In this study, the CH4 production increased by 21.34 % at 20 μM AHLs addition in anaerobic digestion under sulfide stress. AHLs contributed to establishing potential syntrophic relationship between acidifying bacteria (unclassified_o__Bacteroidales, Lentimicrobium, Acetoanaerobium, Longilinea, and Sphaerochaetaa) and Methanothrix. AHLs promoted syntrophic metabolism by boosting microbial metabolic activity and interspecies electron transfer (IET) process under sulfide stress. For microbial metabolic activity, AHLs promoted the key enzyme synthesis in acidogenesis and methanogenesis. For IET process, AHLs promoted the assembly and synthesis of conductive pili, and synthesis and secretion of riboflavin. Furthermore, AHLs promoted microbial self-adaptation including two component system, lipopolysaccharide biosynthesis, and DNA repair, which were important evidences that microbial resistance to sulfide stress was enhanced by AHLs. Microbial self-adaptation provided favorable foundation and safeguard for syntrophic metabolisms under sulfide stress. These findings deciphered the micro-biological mechanisms of AHLs enhancing anaerobic digestion under sulfide stress.

Isolation and characterization of nitroguanidine-degrading microorganisms

Nitroguanidine (NQ) is a component of newly developed insensitive munition (IM) formulations which are more resistant to impact, friction, heat, or sparks than conventional explosives. NQ is also used to synthesize various organic compounds and herbicides, and has both human and environmental health impacts. Despite the wide application and associated health concerns, limited information is known regarding NQ biodegradation, and only one NQ-degrading pure culture identified as Variovorax strain VC1 has been characterized. Here, we present results for three new NQ-degrading bacterial strains isolated from soil, sediment, and a lab-scale aerobic membrane bioreactor (MBR), respectively. Each of these strains -utilizes NQ as a nitrogen (N) source rather than as a source of carbon or energy. The MBR strain, identified as Pseudomonas extremaustralis strain NQ5, is capable of degrading NQ at a rate of approximately 150 μmole L-1 h-1 under aerobic conditions with glucose as a sole carbon source - and NQ as a sole N source. The addition of NH4+ to strain NQ5 during active growth with NQ as a sole N source slowed the growth rate for several hours, and the strain released NH4+, presumably from NQ. When NO3- was added as an alternate N source under similar conditions, the NO3- was not consumed, but NH4+ release into the culture medium was again observed. Strain NQ5 was also able to utilize guanylurea, guanidine, and ethyl allophanate as N sources, and - tolerate salt concentrations as high as 4 % (as NaCl). The other two stains, NQ4 and NQ7, both identified as Arthrobacter spp., grew significantly slower than strain NQ5 under similar culture conditions and tolerated only ∼1 % NaCl. In addition, neither strain NQ4 nor strain NQ7 was able to degrade guanlyurea or ethyl allophanate, but each degraded guanidine. These strains, particularly strain NQ5, may have practical applications for in-situ and ex-situ NQ bioremediation.