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Pseudomonas putida KT2440 is emerging as a promising microbial host for biotechnological industry due to its broad range of substrate affinity and resilience to physicochemical stresses. Its natural tolerance towards aromatics and solvents qualifies this versatile microbe as promising candidate to produce next generation biofuels such as isobutanol. In this study, we scaled‐up the production of isobutanol with P. putida from shake flask to fed‐batch cultivation in a 30 L bioreactor. The design of a two‐stage bioprocess with separated growth and production resulted in 3.35 gisobutanol L–1. Flux analysis revealed that the NADPH expensive formation of isobutanol exceeded the cellular catabolic supply of NADPH finally causing growth retardation. Concomitantly, the cell counteracted to the redox imbalance by increased formation of 2‐ketogluconic thereby providing electrons for the respiratory ATP generation. Thus, P. putida partially uncoupled ATP formation from the availability of NADH. The quantitative analysis of intracellular pyridine nucleotides NAD(P)+ and NAD(P)H revealed elevated catabolic and anabolic reducing power during aerobic production of isobutanol. Additionally, the installation of micro‐aerobic conditions during production doubled the integral glucose‐to‐isobutanol conversion yield to 60 mgisobutanol gglucose–1 while preventing undesired carbon loss as 2‐ketogluconic acid.

Graphical abstract, Highlights • Combined ultrasound and micro aerobic pretreatment for sewage sludge solubilization was assessed. • Low-strength ultrasonic enhanced lipase enzyme activities. • Micro-aerobic pretreatment led to solubilization and increased microbial activity in sewage sludge. • Combined ultrasonic and micro-aeration pre-treatment improved the bio-methane production by 193%. • Combined pretreatment increased energy recovery from anaerobic digestion sewage sludge up to 55%., Low-frequency ultrasonics is a potential technology to reduce the hydrolysis phase period in anaerobic digestion process. In this study, the influence of combined low frequency ultrasonics and micro-aerobic (MA) pretreatment on sewage sludge solubilization, enzyme activity and anaerobic digestion were assessed. Initially, the effect of ultrasonic density (0.012, 0.014, 0.016, 0.018, 0.1, 0.12 and 0.14 W/mL) and irradiation time (1, 3, 5, 8, 9, 10 and 12 min) of 20 kHz frequency waves were investigated. Accordingly, the effect of micro-aerobic pretreatment (Air flow rate (AFR) = 0.1, 0.2, 0.3 and 0.5 VVM) within 20, 30, 40.48 and 60 h were examined. In addition, the effect of combined pretreatment on COD solubilization, lipase enzyme activation, ATP, percentage of live bacteria and methane gas production during the anaerobic process were examined. The results showed that the highest lipase activity (14.9 Umol/mL) was obtained under the effect of ultrasonic density of 0.1 W/ml within 9 min. The highest solubilization (65%) was observed under optimal micro-aerobic conditions: AFR = 0.2 (VVM) and micro-aerobic time: 40 h. Combined ultrasonic and micro-aerobic (US + MA) pretreatment increases the solubilization (70%), microbial activity (2080%) and lipase enzymatic activity (129%) compared to individual pretreatment. The Biogas production during anaerobic digestion pretreated with combined methods increased by 193% compared to the control, while the elevated values of biogas production in reactors pretreated by ultrasonic and micro-aerobic pretreatment alone were observed to be 101% and 165%, respectively. The net energy in reactor with the combined pre-treatment methods was calculated to be 1.26 kWh, while this value for control, pretreated ultrasonic and micro-aerobic reactors were obtained to be 0.56, 0.67 and 1.2 kWh, respectively.

Pseudomonas putida KT2440 is emerging as a promising microbial host for biotechnological industry due to its broad range of substrate affinity and resilience to physicochemical stresses. Its natural tolerance towards aromatics and solvents qualifies this versatile microbe as promising candidate to produce next generation biofuels such as isobutanol. In this study, we scaled‐up the production of isobutanol with P. putida from shake flask to fed‐batch cultivation in a 30 L bioreactor. The design of a two‐stage bioprocess with separated growth and production resulted in 3.35 gisobutanol L–1. Flux analysis revealed that the NADPH expensive formation of isobutanol exceeded the cellular catabolic supply of NADPH finally causing growth retardation. Concomitantly, the cell counteracted to the redox imbalance by increased formation of 2‐ketogluconic thereby providing electrons for the respiratory ATP generation. Thus, P. putida partially uncoupled ATP formation from the availability of NADH. The quantitative analysis of intracellular pyridine nucleotides NAD(P)+ and NAD(P)H revealed elevated catabolic and anabolic reducing power during aerobic production of isobutanol. Additionally, the installation of micro‐aerobic conditions during production doubled the integral glucose‐to‐isobutanol conversion yield to 60 mgisobutanol gglucose –1 while preventing undesired carbon loss as 2‐ketogluconic acid.

Utilization of algicidal bacteria as a biological agent have been receiving significant interest for controlling harmful algal blooms. While various algicidal bacterial strains have been identified, limited studies have explored the influence of bacterial culture conditions on its algicidal activity. Here, the effect of oxygen on the algicidal activity of a novel bacterium JK12, against a model diatom, Phaeodactylum tricornutum (P. tricornutum) was studied. Strain JK12 showed high algicidal activity against P. tricornutum and was identified as Pseudomonas chlororaphis (P. chlororaphis) by 16S ribosomal RNA gene analysis. JK12 culture supernatant exhibited strong algicidal activity while washed JK12 cells showed no obvious activity, indicating that JK12 indirectly attacks algae by secreting extracellular algicidal metabolites. Micro-aerobic culture condition dramatically enhanced the algicidal activity of JK12 by 50%, compared to that cultured under aerobic condition in 24 h. Extracellular metabolomic profiling of JK12 using gas chromatography–mass spectrometry and liquid chromatography–mass spectrometry analysis revealed significantly higher amounts of allantoic acid, urocanic acid, cytidine 2′,3′-cyclic phosphate, uridine 2′,3′-cyclic phosphate, and chlorinated tryptophan in the micro-aerobic culture. This is the first report to demonstrate the important role of oxygen on the algicidal activity of a non-pathogenic strain P. chlororaphis. In addition, the metabolomics analysis provided insights into the algicidal mechanism of P. chlororaphis. Electronic supplementary material The online version of this article (10.1186/s13568-018-0660-x) contains supplementary material, which is available to authorized users.

This study evaluated performance of an upflow membraneless microbial electrolysis cell (MEC) with flow-through electrodes for wastewater treatment. First, methane production and COD removal were evaluated in continuous flow experiments carried out using synthetic and municipal wastewater. A 29-75% increase in methane production was observed under bioelectrochemical conditions as compared to an anaerobic control. Next, simultaneous removal of COD and nitrogen was studied under microaerobic conditions created by continuous air injection to the anodic compartment of the MEC. While the presence of oxygen decreased Coulombic efficiency due to aerobic degradation of COD, enhanced ammonium removal with near zero nitrite and nitrate effluent concentrations was observed. Evidence of direct ammonium oxidation at the anode as well as nitrite and nitrate reduction at the cathode was obtained by comparing performances of MECs operated under anaerobic and microaerobic conditions with the control reactor operated at zero applied voltage.

This study demonstrates enhanced methane production from wastewater in laboratory-scale anaerobic reactors equipped with electrodes for water electrolysis. The electrodes were installed in the reactor sludge bed and a voltage of 2.8–3.5 V was applied resulting in a continuous supply of oxygen and hydrogen. The oxygen created micro-aerobic conditions, which facilitated hydrolysis of synthetic wastewater and reduced the release of hydrogen sulfide to the biogas. A portion of the hydrogen produced electrolytically escaped to the biogas improving its combustion properties, while another part was converted to methane by hydrogenotrophic methanogens, increasing the net methane production. The presence of oxygen in the biogas was minimized by limiting the applied voltage. At a volumetric energy consumption of 0.2–0.3 Wh/L R , successful treatment of both low and high strength synthetic wastewaters was demonstrated. Methane production was increased by 10–25% and reactor stability was improved in comparison to a conventional anaerobic reactor.

Sulphide generated during anaerobic treatment of S-containing wastewaters represents an environmental problem. Adding limited amounts of oxygen or nitrate (or nitrite) to biologically (or chemically) oxidise sulphide forms a simple process level strategy to control this problem. This short review evaluates the feasibility and limitations of this strategy on the basis of the results of bioreactor studies., Spanish Ministry of Education and Science; AEA Technology Environment; Nova Energie; The Swedish Gas Centre; University of Southern Denmark.

A recently discovered thermophilic bacterium, Geobacillus thermoglucosidasius M10EXG, ferments a range of C5 (e.g., xylose) and C6 sugars (e.g., glucose) and is tolerant to high ethanol concentrations (10percent, v/v). We have investigated the central metabolism of this bacterium using both in vitro enzyme assays and 13C-based flux analysis to provide insights into the physiological properties of this extremophile and explore its metabolism for bio-ethanol or other bioprocess applications. Our findings show that glucose metabolism in G. thermoglucosidasius M10EXG proceeds via glycolysis, the pentose phosphate pathway, and the TCA cycle; the Entner?Doudoroff pathway and transhydrogenase activity were not detected. Anaplerotic reactions (including the glyoxylate shunt, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase) were active, but fluxes through those pathways could not be accurately determined using amino acid labeling. When growth conditions were switched from aerobic to micro-aerobic conditions, fluxes (based on a normalized glucose uptake rate of 100 units (g DCW)-1 h-1) through the TCA cycle and oxidative pentose phosphate pathway were reduced from 64+-3 to 25+-2 and from 30+-2 to 19+-2, respectively. The carbon flux under micro-aerobic growth was directed formate. Under fully anerobic conditions, G. thermoglucosidasius M10EXG used a mixed acid fermentation process and exhibited a maximum ethanol yield of 0.38+-0.07 mol mol-1 glucose. In silico flux balance modeling demonstrates that lactate and acetate production from G. thermoglucosidasius M10EXG reduces the maximum ethanol yield by approximately threefold, thus indicating that both pathways should be modified to maximize ethanol production.

Monoethanolamines (MEA) are commonly used as adsorbent in CO2 capture plants. MEA are degraded when used and become a waste product. 3 series of BOD test as well as 9 cases of syringe batch experiments under anaerobic, micro-aerobic and aerobic conditions were conduced to examine the biodegradation of waste amines. BOD and syringe batch experiments indicate that waste amines are successfully degraded and degraded with high reaction rates under all anaerobic, micro-aerobic and aerobic conditions, removing more than 90 % of amine COD. Almost all amine COD was removed in the micro-aerobic case. The BOD experiments show that the amine degradation is in first order reaction, and the highest reaction rate 1.08/d was obtained in reactors with 125 mg/l of initial amine. Even high concentration of amines (2000 mg/l) can be degraded if pH is maintained neutral. Small and compact biological treatment plants therefore can be built to treat waste amines at low cost and meanwhile recover energy as CH4.

The microbial production of ethanol from biodiesel¬derived crude glycerol by Enterobacter aerogenes TISTR1468, under micro-aerobic and anaerobic conditions, was investigated. The experimental results showed that micro-aerobic conditions were more favorable for cellular growth (4.0 g/L DCW), ethanol production (20.7 g/L) as well as the ethanol yield (0.47 g/g glycerol) than anaerobic conditions (1.2 g/L DCW, 6.3 g/L ethanol and 0.72 g/g glycerol, respectively). Crude glycerol (100 g/L) was consumed completely with the rate of 1.80 g/L/h. Two-stage fermentation (combination of micro-aerobic and anaerobic condition) exhibited higher ethanol production (24.5 g/L) than using one-stage fermentation (either micro-aerobic or anaerobic condition. The two- stage configuration, exhibited slightly higher crude glycerol consumption rate (1.81 g/L/h), as well as ethanol yield (0.56 g/g) than the one-stage configuration. Therefore, two-stage process was selected for ethanol production from E. aerogenes TISTR1468 in scale-up studies., {"references":["J. M. Marchetti, V. U. Miguel, and, A. F. Errazu, \"Possible methods for\nbiodiesel production,\" Renew. Sust. Energy. Rev., vol. 11, pp. 1300-1311, 2007.","M. A. Dasari, P. P. Kiatsimkul, W. R. Sutterlin, and G. J. Suppes, \"Low-pressure hydrogenolysis of glycerol to propylene glycol,\" Appl. Catalysis., vol. 281, no. 1-2, pp. 225-231, 2005.","J. C. Thompson, and B. B. He, \"Characterization of the crude glycerol from biodisel production from multiple feedstocks,\" Appl. Eng. Agri., vol. 22, pp. 261-265, 2006.","Z. M. Zheng, Q. L. Hu, J. Hao, F. Xu, N. N. Guo, Y. Sun, and D. H. Liu, \n\"Statistical optimization of culture condition for 1,3-propanediol by Klebsiella pneumoniae AC15 via central composite design,\" Boresour. Technol. vol. 99, pp. 1052-1056, 2008.","S. Sattayasamitsathit, P. Prasertsan, and P. Methacanon, \"Statistical optimization for simultaneous production of 1,3-propanediol and 2,3-butanediol using crude glycerol by newly bacterial isolate,\" Process Biochem vol. 46, pp. 608-614, 2011.","N. Pachauri, and B. He, \"Value-added utilization of crude glycerol from biodiesel production,\" A Survey of Current Research Activities. An ASABE Meeting Presentation, Oregon, 2006.","T. Ito, Y. Nakashimada, K. Senba, T. Matsui, and N. Nishio, \"Hydrogen and ethanol production form glycerol-containing wastes discharged biodiesel manufacturing process,\" J. Biosci. Bioeng., vol. 100, no. 3, pp. 260-265, 2005.","M. F. Temudo, R. Poldermans, R. Kleerebezem, and M. C. M. Loosdrecht, \"Glycerol fermentation by (open) mixed cultures: a chemostat study,\" Biotechnol. Bioeng., vol. 100, pp. 1088-1098, 2008.","A. Gupta, A. Murarka, P. Campbell, and R. Gonzalez, \"Anaerobic fermentation of glycerol in Paenibacillus macerans: metabolic pathways and environmental determinants,\" Appl. Environ. Microbiol., vol. 75, pp. 5871-5883, 2009.\n[10] R. B. Oh, J. W. Seo, S. Y. Heo, W. K. Hong, L. H. Luo, M. H. Joe, D. H. Park, and C. H. Kim, \"Efficient production of ethanol from crude glycerol by a Klebsiella pneumoniae mutant strain,\" Bioresour. Technol., vol. 102, pp. 3918-3922, 2001.\n[11] W. J. Choi, M. R. Hartono, W. H. Chan, and S. S. Yeo, \"Ethanol production from biodiesel-derived crude glycerol by newly isolated Kluyvera cryocrescens,\" Appl. Microbiol. Biotechnol., vol. 89, pp. 1255-1264, 2011.\n[12] C. Tongurai, S. Klinpikul, C. Bunyakan, and P. Kiatsimkul, \"Biodiesel\nproduction from palm oil,\" Songkla. J. Sci. Technol., vol. 23, pp. 831-841, 2001.\n[13] F. Barbirato, S. Astruc, P. Soucaille., C. Camarasa, J. M. Salmon, and A. Bories, \"Anaerobic pathways of glycerol dissimilation by Enterobacter agglomerans CNCM1210: limitations and regulations,\" Microbiol., vol. 43, pp. 2423-2432, 1997.\n[14] E. V. Handel, \"Suggested modification of micro determination of triglycerides,\" Clinical Chem., vol. 7, no. 3, pp. 249-251, 1961.\n[15] X. Chen, D. J. Zhang, V. T. Qi, S. J. Gao, Z. L. Xiu, and P. Xu, \"Microbial fed-batch production of 1,3-propanediol by Klebsiella pneumoniae under micro-aerobic conditions,\" Appl. Microbiol. Biotechnol., vol. 63, pp. 143-146, 2003.\n[16] S. S. Yazdari, and R. Gonzalez, \"Anaerobic fermentation of glycerol: a\npath to economic viability for the biofuels industry,\" Curr. Opin. Biotechnol., vol. 18, pp. 213-219, 2007.\n[17] G. Yang, J. Tian, and J. Li, \"Fermentation of 1,3-propanediol by a lactate deficient mutant of Klebsiella oxytoca under microaerobic conditions,\" Appl. Micronbiol., vol. 73, pp. 1017-1024, 2007."]}