Microbial removal of nitrogen monoxide (NO) under aerobic conditions

Nitrogen oxide gas (NO_x), consisting of nitrogen monoxide (NO) and nitrogen dioxide (NO₂), at a low concentration corresponding to that on roads as a result of exhaust from automobiles, was supplied for 25 days through a laboratory-scale biofilter packed with soil as a packing material. The removal efficiency of NO₂ by soil was almost 100%, and the removal efficiency of NO was 60% on average and 86% at maximum. By using -irradiated soil as a packing material, NO₂ was completely removed mainly by adsorption onto or absorption into the packing material. However, the removal efficiency of NO in the sterilized soil was only 20%, suggesting that NO in soil was removed microbiologically under aerobic conditions.     

Metabolic profiling of Staphylococcus aureus cultivated under aerobic and anaerobic conditions with (1)H NMR-based nontargeted analysis

Staphylococcus aureus is a major pathogen in the medical area and food-producing sector. Detailed analyses of its basic cell physiology will help comprehensively understand this pathogen, which will be useful for developing novel diagnostic and treatment tools. Oxygen is one of the most crucial growth-limiting factors for S. aureus. In this study, to characterize and distinguish metabolic profiles of S. aureus cultivated under aerobic and anaerobic conditions, nontargeted analyses of both types of cultures were carried out using (1)H nuclear magnetic resonance spectroscopy. Fifty compounds were identified by Chenomx software. Characteristics of metabolic profiles were achieved by using principal components analysis. During aerobic growth, S. aureus mainly consumed glucose, alanine, arginine, glycine, isoleucine, leucine, phenylalanine, and acetate. Meanwhile, it accumulated 17 metabolites, mainly 2-oxoglutarate, isobutyrate, isovalerate, succinate, and ethanol. Under anaerobic condition, S. aureus mainly consumed glucose, arginine, and threonine. Meanwhile, it accumulated 13 metabolites, mainly ethanol, lactate, and ornithine. The representative metabolites that could most significantly differentiate metabolic profiles of S. aureus were isobutyrate, isovalerate, and succinate in aerobic cultivation; and lactate, ethanol, and ornithine in anaerobic cultivation. Among these metabolites, isobutyrate and ornithine were present only in aerobic and anaerobic culture, respectively.     

A widely distributed hydrogenase oxidises atmospheric H2 during bacterial growth

Diverse aerobic bacteria persist by consuming atmospheric hydrogen (H₂) using group 1h [NiFe]-hydrogenases. However, other hydrogenase classes are also distributed in aerobes, including the group 2a [NiFe]-hydrogenase. Based on studies focused on Cyanobacteria, the reported physiological role of the group 2a [NiFe]-hydrogenase is to recycle H₂ produced by nitrogenase. However, given this hydrogenase is also present in various heterotrophs and lithoautotrophs lacking nitrogenases, it may play a wider role in bacterial metabolism. Here we investigated the role of this enzyme in three species from different phylogenetic lineages and ecological niches: Acidithiobacillus ferrooxidans (phylum Proteobacteria), Chloroflexus aggregans (phylum Chloroflexota), and Gemmatimonas aurantiaca (phylum Gemmatimonadota). qRT-PCR analysis revealed that the group 2a [NiFe]-hydrogenase of all three species is significantly upregulated during exponential growth compared to stationary phase, in contrast to the profile of the persistence-linked group 1h [NiFe]-hydrogenase. Whole-cell biochemical assays confirmed that all three strains aerobically respire H₂ to sub-atmospheric levels, and oxidation rates were much higher during growth. Moreover, the oxidation of H₂ supported mixotrophic growth of the carbon-fixing strains C. aggregans and A. ferrooxidans. Finally, we used phylogenomic analyses to show that this hydrogenase is widely distributed and is encoded by 13 bacterial phyla. These findings challenge the current persistence-centric model of the physiological role of atmospheric H₂ oxidation and extend this process to two more phyla, Proteobacteria and Gemmatimonadota. In turn, these findings have broader relevance for understanding how bacteria conserve energy in different environments and control the biogeochemical cycling of atmospheric trace gases.Subject terms: Environmental microbiology, Biogeochemistry     

Metabolism of L(−)-carnitine by Enterobacteriaceae under aerobic conditions

Different Enterobacteriaceae, such as Escherichia coli, Proteus vulgaris and Proteus mirabilis, are able to convert L(-)-carnitine, via crotonobetaine, into gamma-butyrobetaine in the presence of carbon and nitrogen sources under aerobic conditions. Intermediates of L(-)-carnitine metabolism (crotonobetaine, gamma-butyrobetaine) could be detected by thin-layer chromatography. In parallel, L(-)-carnitine dehydratase, carnitine racemasing system and crotonobetaine reductase activities were determined enzymatically. Monoclonal antibodies against purified CaiB and CaiA from E. coli O44K74 were used to screen cell-free extracts of different Enterobacteriaceae (E. coli ATCC 25922, P. vulgaris, P. mirabilis, Citrobacter freundii, Enterobacter cloacae and Klebsiella pneumoniae) grown under aerobic conditions in the presence of L(-)-carnitine.     

Iron is maintained as Fe(II) under aerobic conditions in erythroid cells

It was found that in rabbit erythrocytes loaded with Fe(II) (using the ionophore, A23187) over 90% of this metal is maintained in its ferrous form. In rabbit reticulocytes more than 50% of the transferrin-donated nonheme iron proved to be divalent. These results strongly suggest that under aerobic conditions the intracellular environment of intact erythroid cells is reducing for iron.     

Bio-oxidation of tripropylene glycol under aerobic conditions

Aerobic biodegradation of tripropylene glycol (PG3) was investigated under the conditions of the OECD screening test 301E and the Continuous Flow Activated Sludge Simulation test (CFAS). A modified two-chamber facility with a denitrification stage was used for the CFAS test. Primary PG3 biodegradation was measured by the HPLC with fluorimetric detection and analyte derivatisation. Metabolites were identified by LC-MS with electrospray ionisation and GC-MS with electron impact ionisation, as well as semiquantitatively determined by the LC-MS technique. PG3 was found to be inherently biodegradable and it exhibits a strong poisonous effect on activated sludge after exceeding the threshold concentration (10 mg l⁻¹). Metabolite accumulation onto the activated sludge is probably responsible for this poisonous effect. Probable biotransformation products of tripropylene glycol under the aerobic conditions include metabolites with a single terminal aldehyde or a ketone group and metabolites with two terminal aldehyde or ketone groups. Their concentration rises at the end of the OECD screening test.     

Novel cytotoxic chelators that bind iron(II) selectively over zinc(II) under aqueous aerobic conditions

To achieve cellular iron deprivation by chelation, it is important to develop chelators with selective metal-binding properties. Selectivity for iron has long been the province of certain oxygen-donor chelators such as desferrioxamine, which target Fe(III) and exploit the strength of a relatively ionic Fe(III)-O interaction. We have been studying novel chelators that possess mechanisms to selectively chelate +2 biometals, particularly tachpyr [N,N',N"-tris(2-pyridylmethyl)-1,3,5-cis,cis-triaminocyclohexane] and derivatives from N,N',N"-trialkylation and pyridine ring alkylation. Metal-exchange and metal-binding competition reactions have been conducted at pH 7.4, 37 degrees C and time periods until no further change was observed (generally 24-48 h). Under anaerobic conditions, tachpyr is strongly selective for iron, binding 95+/-5% Fe(II) versus 5+/-5% Zn(II) in the forms [Fe(tachpyr)](2+) and [Zn(tachpyr)](2+) respectively. Under aerobic conditions, tachpyr complexes Fe(II) more effectively than Fe(III), forming iminopyridyl complexes [Fe(tachpyr-ox-n)](2+) (n=2, 4) by O(2)-induced and iron-mediated oxidative dehydrogenation. Complexes [Fe(tachpyr-ox-n)](2+) are also strongly bound forms of iron that are unaffected by an excess of Zn(II) (75 mol zinc:1 mol iron complex). The preference of tachpyr for iron over zinc under aerobic conditions appears to be hindered by oxidation of Fe(II) to Fe(III), such that the proportions bound are 44+/-10% Fe(II) versus 56+/-10% Zn(II), in the respective forms [Fe(tachpyr-ox-n)](2+) and [Zn(tachpyr)](2+). However, upon addition of the reducing agent Na(2)S(2)O(4) that converts Fe(III) to Fe(II), the binding proportions shift to 76+/-10% Fe(II) versus 24+/-10% Zn(II), demonstrating a clear preference of tachpyr for Fe(II) over Zn(II). Iron(II) is in the low-spin state in [Fe(tachpyr)](2+) and [Fe(tachpyr-ox-n)](2+) (n=2, 4), which is a likely cause of the observed selectivity. N-methylation of tachpyr [giving (N-methyl)(3)tachpyr] results in the loss of selectivity for Fe(II), which is attributed to the steric effect of the methyl groups and a resulting high-spin state of Fe(II) in [Fe(N-methyl)(3)tachpyr)](2+). The relationship of chelator selectivity to cytotoxicity in the tach family will be discussed.     

Survival of a Salmonella typhimurium poultry isolate in the presence of propionic acid under aerobic and anaerobic conditions

Propionic acid is commonly found as a fermentation product in the gastrointestinal tracts of food animals and has also been used to limit the microbial contaminants in animal feeds. Because propionic acid is known to have antibacterial activity, the propionic acid encountered by foodborne pathogens during their life cycles may play an important role in inhibiting the survival of the pathogens. The survival patterns of Salmonella typhimurium poultry isolate were determined both in aerobic and anaerobic tryptic soy broth (TSB; pH 5.0 or 7.0) containing various concentrations of propionic acid (0-200 mM). The levels of recovered cells were consistently greater at pH 7.0 compared to those at pH 5.0. For the first 4 days, the levels were significantly decreased by incubation under anaerobic conditions as compared to aerobic condition at pH 7.0 (P<0.05). However, there were fluctuations of cell populations with different patterns depending on both concentrations and growth conditions. To characterize the nature of the capability which allowed the cell multiplication following decreases in cell population during incubation at pH 7.0, the cells isolated from the outgrowth cultures were tested for survival in aerobic or anaerobic TSB (pH 5.0 or pH 7.0) containing propionic acid (50 mM). The outgrowth isolates did not show significant differences in the level of recovered cells in the presence of propionic acid when compared to the wild type strain (P>0.05), suggesting that the cells in the outgrowth cultures did not harbour mutation(s) conferring increased resistance to propionic acid. In addition, the level of recovered cells of isogenic rpoS mutant strain of S. typhimurium was not significantly different from that of the wild type strain in the same assay conditions (P<0.05). The results of this study show that the bactericidal activity of propionic acid on S. typhimurium can be affected by environmental conditions such as acidic pH levels and anaerobiosis in food materials and gastrointestinal tracts. However, S. typhimurium is also able to multiply in the presence of sublethal concentrations of propionic acid at neutral pH during prolonged incubation under both aerobic and anaerobic conditions.     

Degradation of mangrove leaf litter under aerobic conditions

Degradation ofAvicennia marina (Forsk) Vierh. leaf litter was studied in the laboratory for three months. The leaves were incubated in filtered estuarine water in erlenmeyer flasks for various number of days and the amounts of N, P, and K⁺ remaining in the leaves determined. Weight loss was rapid within the first 24 hours (19%), but slowed down thereafter reaching 30% after six weeks. While P and K⁺ decreased with time, N decreased initially, then increased rapidly after six weeks. Leaching and microbial activities could be responsible for the nutrient changes. The increase in N may indicate that mangrove leaf litter provides the surface for microbial N synthesis and acts as a reservoir for N.     

The impact of feed composition on biodegradation of benzoate under cyclic (aerobic/anoxic) conditions

The response of a mixed microbial culture to different feed compositions, that is, containing benzoate and pyruvate as sole carbon sources at different levels, was studied in a chemostat with a 48-h hydraulic residence time under cyclic aerobic and anoxic (denitrifying) conditions. The cyclic bacterial culture was well adapted to different feed compositions as evidenced by the lack of accumulation of benzoate or pyruvate in the chemostat. Both the benzoate-degrading capabilities and the in vitro catechol 2,3-dioxygenase (C23DO) activities of the cyclic bacterial cultures were in direct proportion to the flux through the chemostat of the substrate degraded by the pathway containing C23DO, with some exceptions. The quantity of C23DO showed a transient decrease during the initial portion of the aerobic period before returning to the level present during the anoxic period. That decrease was most likely caused by the production of H(2)O(2) by the cells upon being returned to aerobic conditions.     

Salmonella typhimurium synthesizes cobalamin (vitamin B12) de novo under anaerobic growth conditions.

In this paper, we report that the enteric bacterium Salmonella typhimurium synthesized cobalamin de novo under anaerobic culture conditions. Aerobically, metE mutants of S. typhimurium need either methionine or cobalamin as a nutritional supplement for growth. The growth response to cobalamin depends upon a cobalamin-requiring enzyme, encoded by the gene metH, that catalyzes the same reaction as the metE enzyme. Anaerobically, metE mutants grew without any nutritional supplements; the metH enzyme functioned under these conditions due to the endogenous biosynthesis of cobalamin. This conclusion was confirmed by using a radiochemical assay to measure cobalamin production. Insertion mutants defective in cobalamin biosynthesis (designated cob) were isolated in the three major branches of the cobalamin biosynthetic pathway. Type I mutations blocked the synthesis of cobinamide, type II mutations blocked the synthesis of 5,6-dimethylbenzimidazole, and type III mutations blocked the synthesis of cobalamin from cobinamide and 5,6-dimethylbanzimidazole. Mutants that did not synthesize siroheme (cysG) were blocked in cobalamin synthesis. Genetic mapping experiments showed that the cob mutations are clustered in the region of the S. typhimurium chromosome between supD (40 map units) and his (42 map units). The discovery that S. typhimurium synthesizes cobalamin de novo only under anaerobic conditions raises the possibility that anaerobically grown cells possess a variety of enzymes which are dependent upon cobalamin as a cofactor.     

Alternative and cyclic appearance of H2 and O2 photoproduction activities under non-growing conditions in an aerobic nitrogen-fixing unicellular cyanobacterium Synechococcus sp.

With synchronously grown cells of an aerobic unicellular marine cyanobacterium Synechococcus sp. Miami BG 043511, changes in the activities of anoxygenic, nitrogenase-dependent hydrogen photoproduction and oxygen photoevolution were measured under non-growing hydrogen production conditions. Interestingly, synchronously grown cells, incubated in light under an argon atmosphere, exhibited cyclic changes in the activity of nitrogenase-catalyzed hydrogen production for approximately 20- to 25-h intervals. Cyclic photosynthetic oxygen production activity also appeared in approximately the same intervals. However, changes in hydrogen production and oxygen production activities were inversely correlated and temporally separated. Stepwise accumulation of hydrogen in closed vessels was also observed in approximately 24-h cycles in these non-growing cells. These observations in non-growing cells suggest that this unicellular aerobic, nitrogen-fixing cyanobacterium may have an endogenous system to control the exhibition of cyclic rhythms, in addition to the previously studied cell cycle-oriented system. Expression and switching between these two systems may be related to the sufficiency or insufficiency of nitrogen growth nutrients. The possibility of the existence of a common control factor of the two systems involving glycogen is also discussed.     

Biodegradation of p-aminoazobenzene by Bacillus subtilis under aerobic conditions

Biological oxidation of organic dyes is important for textile industry wastewater treatment. The aim of this work was to assess the biodegradation kinetics of a specific azo-dye, p-aminoazobenzene. The degradation of p-aminoazobenzene by Bacillus subtilis was examined through batch experiments in order to investigate the effect of p-aminoazobenzene on the bacterial growth rate and elucidate the mechanism of dye degradation. The results proved that B. subtilis cometabolizes p-aminoazobenzene in the presence of glucose as carbon source, producing aniline and p-phenylenediamine as the nitrogen–nitrogen double bond is broken. The azo-dye was found to act as an inhibitor to microbial growth. A mathematical model was developed that describes cellular growth, glucose utilization, p-aminoazobenzene degradation and product formation. Received 26 July 1996/ Accepted in revised form 14 May 1997     

Acetic acid increases stability of silage under aerobic conditions

The effects of various compounds on the aerobic stability of silages were evaluated. It has been observed that inoculation of whole-crop maize with homofermentative lactic acid bacteria leads to silages which have low stability against aerobic deterioration, while inoculation with heterofermentative lactic acid bacteria, such as Lactobacillus brevis or Lactobacillus buchneri, increases stability. Acetic acid has been proven to be the sole substance responsible for the increased aerobic stability, and this acid acts as an inhibitor of spoilage organisms. Therefore, stability increases exponentially with acetic acid concentration. Only butyric acid has a similar effect. Other compounds, like lactic acid, 1,2-propanediol, and 1-propanol, have been shown to have no effect, while fructose and mannitol reduce stability.     

Microbial decolorization of reactive azo dyes under aerobic conditions

Summary Kodam et al. reported a 100% decolorization of the sulfonated azo dyes Reactive Red 2, Reactive Red 141, Reactive Orange 4, Reactive Orange 7 and Reactive Violet 5 by an unidentified bacterium, KMK 48. High effectiveness was attained within 36 h of incubation at room temperature and neutral pH. Optimum decolorization took place strictly under aerobic conditions, which is contrary to other well-documented reports. Thus, this microorganism seems to be potentially effective for bioremediation of textile-dyeing industry effluents.