The effect of sodium chlorate and nitrapyrin on the nitrification mediated nitrosation process in soils

Summary The influence of total nitrification to nitrate or partial nitrification to nitrite on the soil organic nitrogen status was examined. NH ₄ ⁺ –¹⁵N was added to the soil in the absence and the presence of NaClO₃, respectively nitrapyrin. The first chemical inhibits only nitrate formation, the second inhibits total nitrification. The accumulation of nitrite nitrogen in the soil at levels up to 5 mg kg^–1 increased the loss of nitrogen. Yet, it did not increase the binding of mineral nitrogen into soil organic matter, relative to the control soil. The data suggest that the biochemistry of the nitrite formation process, rather than the levels of nitrite ions formed, are of primary importance in the role of nitrification mediated nitrosation of soil organic matter.     

Lactic acid bacteria: Micro-organisms able to grow in the absence of available iron and copper

Summary The growth of different species of the genera Lactobacillus, Streptococcus, Pediococcus and Leuconostoc was followed in media in which all available iron and copper was chelated by 2,2-dipyridyl. None of the species tested was inhibited in its growth. Iron and copper complexation, by means of chemical scavengers, could be a useful method to direct non-axenic lactic fermentations.     

The effect of the H2 partial pressure on the metabolite pattern ofLactobacillus casei,Escherichia coli andClostridium butyricum

Summary The metabolite pattern of batch cultures ofLactobacillus casei LMG 6400,Clostridium butyricum LMG 1213t1 andEscherichia coli LMG 2093 was effected only for the latter organism when the H₂ partial pressure was below 1 atmosphere: high hydrogen partial pressures increased the formate formation, low pressures gave rise to increased acetate production and higher cell yields.     

Nitrification and organic nitrogen formation in soils

Summary The formation of mineral nitrogen species and of organic nitrogen was studied in three different types of soils in relation to the application of the nitrification inhibitor nitrapyrin. The results indicate that nitrification brings about a deficit in total mineral nitrogen and a concomitant surplus in non biomass organic nitrogen. This phenomenon increases with increasing levels of applied ammonium nitrogen and soil organic matter. The phenomenon is considered to be due to the reaction of the transient nitrite formed with soil phenolic compounds and appears to be of significance in all soils in which nitrification occurs, even neutral to alkaline and low carbon soils.     

Conversion of organic acids to h(2) by Rhodospirillaceae grown with glutamate or dinitrogen as nitrogen source

Axenic cultures of Rhodopseudomonas capsulata. Rhodospirillum rubrum, and Rhodomicrobium vannielii grown with glutamate as the nitrogen source converted lactate, acetate, and butyrate to H(2) and CO(2). Conversion rates ranged from 100 to 926 mL H(2) L(r) (-1) day(-1) (where L(r) is the reactor contents), and efficiencies varied from 23 to 100% When grown with N(2), conversion rates up to 760 mL H(2) L(r) (-1) day(-1) and efficiencies up to 100%were achieved. Upon aging, cultures appear to rapidly increase in hydrogen uptake activity and furthermore decrease in nitrogenase activity, both factors leading to a slowdown of hydrogen production. This was particularly the case for diazotrophically grown photobacteria.     

Distribution of extracellular polysaccharides and flotation of anaerobic sludge

 Extracellular polysaccharides (EPS) were quantified in dense granules and loose flocs by chemical analysis of the uronic acid content. Their distribution within the aggregates was determined by microscopic staining. Granules contained a higher amount of EPS (1–1.6 mg/g volatile suspended solids, VSS) than flocs (0.3 mg/g VSS). In granules approximately 50% of the total amount of EPS was present in a 40-μm-thick zone on the surface. The remainder was dispersed in the rest of the aggregate. In flocs the highest concentration was present in the centre and the EPS layer on the surface was not found. Tests showed that flocculent sludge was very sensitive to flotation, while the studied granules did not float. The lower susceptibility to flotation of granules as compared to flocs was attributed to the presence of the hydrophilic EPS coating that prevents attachment of gas bubbles. Received: 21 November 1995/Received last revision: 15 April 1996/Accepted: 22 April 1996     

Mass transfer limitation of sulfate in methanogenic aggregates

The role of mass transfer limitation of sulfate as a factor governing the competition between sulfate reducing and methane producing bacteria in methanogenic aggregates was theoretically evaluated by the calculation of steady-state sulfate microprofiles using a reference set of parameters obtained from the literature. The shooting method was used as a numerical technique for solving the mathematical model. The effect of the parameters on mass transport limitation was tested by varying each reference value of the parameters with a factor of 3. Sulfate limitation within granules prevailed at moderate (0.1 kg m(-3)) and low sulfate concentrations in the bulk liquid, at high maximum sulfate utilization rates (3.73 x 10(-5) kg SO(4) (2-) kg(-1) VSS S(-1) or biomass concentrations (40 KG VSS m(-3)), and in large aggregates (radius of 7.5 10(-4) m). The effective diffusion coefficient of sulfate and the affinity constant were less determinative for the penetration depth of sulfate within a granule. (c) 1994 John Wiley & Sons, Inc.     

Gene disruption in Lactobacillus plantarum strain 80 by site-specific recombination: isolation of a mutant strain deficient in conjugated bile salt hydrolase activity

A chloramphenicol-resistance gene (cml) was introduced into the Lactobacillus plantarum gene encoding conjugated bile acid hydrolasc (cbh) on a ColEl replicon. This plasmid which is nonreplicative in Lactobacillus was used to transform L. plantarum strain 80. A homologous double cross-over recombination event resulted in replacement of the chromosomal cbh gene by the cml-containing cbh gene. The transformants obtained were unable to synthesize active conjugated bile acid hydrolase (Cbh). The Cbh-Cml^R phenotype was stably maintained for more than 100 generations under nonselective conditions.This paper is dedicated with great appreciation to Dr. Frits Berends on the occasion of his retirement as Head of the Biochemistry Department of the TNO Medical Biological Laboratory     

Thermophilic,anaerobic degradation of gelatin by Thermobacteroides proteolyticus

Summary The anaerobic thermophilic proteolysis of gelatin by Thermobacteroides proteolyticus (strain BT = ATCC 35245) was investigated. Gelatin was fermented within 5 to 7 days to mainly acetic acid, isobutyric acid, isovaleric acid, and ammonium. Carbon dioxide and hydrogen were produced as well. Maximal ammonification of organic-N was observed at an initial gelatin concentration greater than 2.7 and lower than 10 g/l. Gelatin degradation was not influenced when various amounts of yeast extract (0 to 1 g/l) or ammonium chloride (0 to 6 g/l) were added to the medium.     

Survival potential of Aeromonas hydrophila in freshwaters and nutrient-poor waters in comparison with other bacteria

The survival of a genetically-marked Aeromonas hydrophila strain was studied in water microcosms using viable counts. Aeromonas hydrophila AWWX1 was shown to survive without decline in viable counts for at least 10 d in three of four filtered-autoclaved freshwaters (surface water and groundwater) and in all examined filtered-autoclaved nutrient-poor waters (bottled spring water, Milli-Q and tap water). However, in the unfiltered waters, a rapid decrease in viable counts of Aer. hydrophila AWWX1 was observed after 1–5 d. The survival of Aer. hydrophila AWWX1 in nutrient-poor waters was compared with that of Pseudomonas fluorescens P17 and Spirillum strain NOX. Survival characteristics were organism- and water-dependent. In the filtered-autoclaved waters, viable counts of Spirillum strain NOX were ca 1 log-unit higher than for Aer. hydrophila AWWX1 and Ps. fluorescens P17. The tested strains Aer. hydrophila AWWX1 and Ps. fluorescens P17 survived 3 to 20, respectively 2 to 4 times better in the filtered-autoclaved waters compared to the unfiltered waters. Apparently, any inherent capability of these micro-organisms to adapt to low-nutrient environments was undone by the presence of the autochthonous microbiota. The present findings that Aer. hydrophila survives very poorly in several drinking waters is of utmost importance towards public health and arises questions about the mechanisms involved.