Nitrate assimilation by marine heterotrophic bacteria

Nitrate assimilation is a process where bacteria utilize nitrate as a nitrogen source and synthesize it into organic nitrogen. We found that nitrate-assimilating bacteria(NAB) are widely distributed in various marine environments, from surface to the deep ocean and sediment, which indicates that NAB are significant to the oceanic nitrogen cycle. Comparative genomic analysis revealed nitrate-assimilating genes(nas A) in these marine heterotrophic NAB showed different gene arrangements and diverse regulation systems. Summary on recent findings will contribute to understanding the process of nitrate assimilation in NAB and their ecological significance in the nitrogen cycle. A systematic analysis of a number of studies on bacterial nitrate assimilation in marine ecological systems was conducted to clarify directions for future research.

Nitrate removal and extracellular polymeric substances of autohydrogenotrophic bacteria under various pH and hydrogen flow rates

In recent years there has been an increasing interest in the use of autohydrogenotrophic bacteria to treat nitrate from wastewater. However, our knowledge about the characteristics of extracellular polymeric substances（EPS） releasing by these activities is not yet very advanced. This study aimed to investigate the change in EPS compositions under various p H values and hydrogen flow rates, taking into consideration nitrogen removal. Results showed that p H 7.5 and a hydrogen flow rate of 90 m L/min were the optimal operating conditions, resulting in 100% nitrogen removal after 6 hr of operation. Soluble and bound polysaccharides decreased, while bound proteins increased with increasing p H. Polysaccharides increased with increasing hydrogen flow rate. No significant change of bound proteins was observed at various hydrogen flow rates.

Microbiologically influenced corrosion of Cu by nitrate reducing marine bacterium Pseudomonas aeruginosa

The microbiologically influenced corrosion(MIC) mechanisms of copper by Pseudomonas aeruginosa as a typical strain of nitrate reducing bacteria(NRB) was investigated in this lab study.Cu was immersed in deoxygenated LB-NO3 seawater inoculated with P.aeruginosa and incubated for 2 weeks.Results showed that this NRB caused pitting and uniform corrosion.The maximum pit depths after 7 d and 14 d in125 mL anaerobic vials with 50 mL broth were 5.1 μm and 9.1 μm,accompanied by specific weight losses of 1.3 mg/cm2(7 d) and 1.7 mg/cm2(14 d),respectively.Electrochemical measurements corroborated weight loss and pit depth data trends.Experimental results indicated that extracellular electron transfer for nitrate reduction was the main MIC mechanism and ammonia secreted by P.aeruginosa could also play a role in the overall Cu corrosion process.

Overlooked nitrogen-cycling microorganisms in biological wastewater treatment

Nitrogen-cycling microorganisms play key roles at the intersection of microbiology and wastewater engineering.In addition to the well-studied ammonia oxidizing bacteria,nitrite oxidizing bacteria,heterotrophic denitrifiers,and anammox bacteria,there are some other N-cycling microorganisms that are less abundant but functionally important in wastewater nitrogen removal.These microbes include,but not limited to ammonia oxidizing archaea(AOA),complete ammonia oxidation(comammox)bacteria,dissimilatory nitrate reduction to ammonia(DNRA)bacteria,and nitrate/nitrite-dependent anaerobic methane oxidizing(NO_(x)-DAMO)microorganisms.In the past decade,the development of high-throughput molecular technologies has enabled the detection,quantification,and characterization of these minor populations.The aim of this review is therefore to synthesize the current knowledge on the distribution,ecological niche,and kinetic properties of these“overlooked”N-cycling microbes at wastewater treatment plants.Their potential applications in novel wastewater nitrogen removal processes are also discussed.A comprehensive understanding of these overlooked N-cycling microbes from microbiology,ecology,and engineering perspectives will facilitate the design and operation of more efficient and sustainable biological nitrogen removal processes.