Nitrogenase Activity In Cultures Research Articles

Degradation and Colonization of Cellulose by Diazotrophic Strains of Paenibacillus polymyxa Isolated from Soil

The bioconversion of cellulose to soluble sugars by diazotrophic bacteria is a very important for the environment, such as for the global stabilization and a sustainable human society. Two nitrogen-fixing microorganisms hydrolyzing cellulose were isolated from agricultural soil and identified as Paenibacillus polymyxa [the laboratory names EG2 and EG14] based on 16Sr RNA sequence. The genome of these bacteria was found to carry nif genes coding the individual components of the nitrogenase complex. Their nitrogen fixing ability was confirmed by studying nitrogenase activity in cultures of the studied bacteria in N-free medium supplemented with carboxymethylcellulose (CMC). The nitrogenase activity of P. polymyxa EG 2 was 2.9 nM C2H4∙ml-1∙h-1 whereas P. polymyxa EG 14 0.4nM C2H4∙ml-1∙h-1. The isolates in medium with filter paper synthesize following cellulolytic enzymes: carboxymethylcellulase (CMCase), FPase and Avicellase. Of the cellulolytic enzymes in the culture supernatants of the bacteria the most abundant was CMCase (P. polymyxa EG 2 103.4 mU, EG 14:96.1 mU) with far lower amounts of enzymes hydrolyzing crystalline Avicel cellulose or filter paper. In spite of these observations the better isolate in terms of synthesis of cellulases is P. polymyxa EG 14. Zymograms reflecting the main cellulase activities of the studied bacteria do not significantly differ from each other and present at least three major enzymatic activities with high molecular masses: one of about 200 kDa, another of about 220 kDa and a strong band of activity with mass of about 130 KDa. Observations of the bacterial cultures in medium with filter paper revealed the colonization of the substrate by single cells or aggregates of bacterial cells surrounded by slime. Scanning and transmission microscopy of the isolates revealed the presence of spherical structures resembling cellulosomes on the surface of the bacteria being characteristic for anaerobic bacteria of the genus Clostridium.

Sensitivity of selected Frankia isolates from Casuarina, Allocasuarina and North American host plants to sodium chloride

Three experiments examined the effects of NaCl concentrations 0 to 500 mM on the growth of isolates of Frankia from Casuarinaceae and selected North American host plants. Four Casuarina isolates grew well in defined medium (pyruvate‐BAP) but not in a yeast extract medium. Conversely the non‐Casuarina isolates preferred the yeast‐extract medium, although two of them grew in the defined medium. When grown in their preferred medium, the Casuarina isolates were little affected by NaCl concentrations up to 200 mM but did not grow at 500 mM. The non‐Casuarina isolates, with the exception of an isolate from Purshia tridentata. were severely affected above 50 mM NaCl.Nitrogenase activity (C2H2 reduction) by the non‐Casuarina isolates could not be detected in low‐N medium although protein determinations indicated that a low level of nitrogen fixation had occurred. All four Casuarina isolates showed nitrogenase activity in culture, up to 200 mM NaCl, although at that concentration of NaCl, growth was affected more than that of cultures in N‐supplemented medium. All four strains showed a marked increase in nitrogenase activity up to 72 h after the addition of C2H2, with the magnitude of the effect and their subsequent behaviour being strain dependent.The results indicate that the isolates of Frankia from Casuarina and Allocasuarina, and that from Purshia tridentata, are more tolerant of NaCl than isolates from species not normally growing under sodic conditions. They provide optimism that these strains could successfully establish in saline soils if introduced with species of host plants tolerant to these soils.

THE EFFECT OF ABSCISIC ACID ON CALCIUM‐MEDIATED REGULATION OF HETEROCYST FREQUENCY AND NITROGENASE ACTIVITY IN NOSTOC 6720

SummaryAbscisic acid (ABA) promoted a significant increase of the heterocyst frequency in cultures of Nostoc 6720. A significant interaction between ABA and the concentration of Ca2+ in the growth medium was detected. Studies using 45Ca2+ confirmed that the intracellular Ca2+ content was raised by 20% in the presence of 10−6 M ABA. Verapamil, a Ca2+ channel antagonist, inhibited the ABA‐induced increase in heterocyst frequency. Trifluoroperazine, a known inhibitor of Ca2+/protein binding, also inhibited the response to ABA.The characteristics of the response to ABA were similar to those of the Ca2+ ionophore, A23187. Both promote an increase in the total nitrogenase activity of the culture, which, it is suggested, may result from a Ca2+‐dependent protective mechanism similar to that proposed for Gleocapsa. A Ca2+‐dependent repression of dinitrogen fixation is suggested to account for the increased nitrogenase activity in cultures induced to form heterocysts in the presence of lanthanum or when the concentration of Ca2+ in the growth medium is less than 10−4 M.

Correlation between rifampicin-resistance of slow-growing Rhizobium strains and their ability to express nitrogenase activity in culture

Correlation between rifampicin-resistance of slow-growing Rhizobium strains and their ability to express nitrogenase activity in culture

Correlation between rifampicin-resistance of slow-growingRhizobiumstrains and their ability to express nitrogenase activity in culture

Correlation between rifampicin-resistance of slow-growing<i>Rhizobium</i>strains and their ability to express nitrogenase activity in culture

Dinitrogen Fixation by Cultures of Frankia sp CpIl Demonstrated by 15N2 Incorporation

The filamentous bacterium Frankia of the Actinomycetales, isolated from the nitrogen-fixing root nodules of certain woody plants, has shown nitrogenase activity in culture, using the acetylene reduction method. In the present work, nitrogenase activity in pure cultures of Frankia sp. CpIl is confirmed using mass spectrometric measurements of (15)N(2) incorporation. After addition of carrier NH(4) (+) to digested cultures, those exposed to (15)N(2) (25 atom%) had a (15)N content of 3.16 atom% compared to 0.354 atom% (15)N in the controls.

Nitrogen fixation in nitrate reductase-deficient mutants of cultured rhizobia.

Forty-eight mutants unable to reduce nitrate were isolated from "cowpea" Rhizobium sp. strain 32Hl and examined for nitrogenase activity in culture. All but two of the mutants had nitrogenase activity comparable with the parental sttain and two nitrogenase-defective strains showed alterations in their symbiotic properties. One strain was unable to nodulate either Macroptilium atropurpureum or Vigna uguiculata and, with the other, nodules appeared promptly, but effective nitrogen fixation was delayed. These results, and the relatively low proportion of nitrate reductase mutants with impaired nitrogenase activity, do not support the proposed commanality between nitrogenase and nitrate reductase in cowpea rhizobia. Inhibition studies of the effect of nitrate and its reduction products on the nitrogenase activity in cultured strains 32Hl and the nitrate reductase-deficient, Nif+ strains, indicated that nitrogenase activity was sensitive to nitrite rather than to nitrate.