Rhizobium bacteria

The flavonoids are a remarkable group of plant metabolites. No other class of secondary product has been credited with so many — or such diverse — key functions in plant growth and development. Many of these tasks are critical for survival, such as attraction of animal vectors for pollination and seed dispersal, stimulation of Rhizobium bacteria for nitrogen fixation. 

Inoculation with specific strains of rhizobium bacteria stimulates nodulation on leguminous forbs, Commercial inoculants are available for the important legume species. Rhizobium bacteria may not survive or produce effective nodules in acidic spoils with pH below 5.0. 

Most chemical reactions give off heat and are classified as exothermic reactions. The rate of a reaction may be calculated by the Arrhenius equation, which contains absolute temperature, K, equal to the Celsius temperature plus 273, in an exponential term. As a general rule, the speed of a reaction doubles for each 10°C increase in temperature. Reaction rates are important in fires or explosions involving hazardous chemicals. A remarkable aspect of biochemical reactions is that they occur rapidly at very mild conditions, typically at body temperature in humans (see Chapter 3). For example, industrial fixation of atmospheric elemental nitrogen to produce chemically bound nitrogen in ammonia requires very high temperatures and pressures, whereas Rhizobium bacteria accomplish the same thing under ambient conditions. 

The NH3 can then be further converted into nitrate or nitrite or directly used in the synthesis of amino acids and other essential compounds. This reaction takes place at 0.8 atm N2 pressure and ambient temperatures in Rhizobium bacteria in nodules on the roots of legumes such as peas and beans, as well as in other independent bacteria. In contrast to these mild conditions, industrial synthesis of ammonia requires high temperatures and pressures with iron oxide catalysts, and even then yields only 15% to 20% conversion of the nitrogen to ammonia. Intensive efforts to determine the bacterial mechanism and to improve the efficiency of the industrial process have so far been only moderately successful the goal of approaching enzymatic efficiency on an industrial scale is still only a goal. 

Although many microorganisms are apparently capable of denitrification, only a few specialized species, including the free-living Azotobacter, blue-green algae, some anaerobic bacteria, and Rhizobium bacteria in root nodules of legumes, are ca-... 

The signals from a number of plants involved in nodula-tion by Rhizobium bacteria are now known (see above). Those of Phaseolus vulgaris, black bean, for Rhizobium le-... 

The interactions of Rhizobium bacteria and plants of the Fabaceae are highly specific. It is believed that lectins play a major role in this specificity (Etzler, 1986, Liener, 1991 Sharon and Lis, 1989). Several models have been proposed to explain this interaction. The lectin appears to act as a glue to hold the bacterium in place (Rudiger, 1984). It appears that binding of host lectins may send a signal to the bacterium that turns on a gene, which leads to the synthesis of a specific polysaccharide on the bacterial cell wall that serves as a receptor site for the lectin (Liener, 1991). 

Isol. from nitrogen-fixing Rhizobium bacteria. Biosynth. intermediate for 1,... 

These are potentially attractive to replace imports particularly with the concern about using products from genetically modified crops. New varieties from Eastern European breeding programmes are now available and have potential for production in southern England in good years and the seed should be inoeulated y/ith Rhizobium bacteria. 

Lupins require a pH below 7 and the seed should be inoculated Wiih Rhizobium bacteria to encourage nodulation. It is important to establish a good plant population and time of sowing is critical for winter varieties. The crop does not require nitrogen and on fertile soils has little requirement for phosphate and potash. Crop protection products ate available but generally with Extensions of Authorisation for Minor Uses (EAMUs) approval and advice should be obtained. 

Rhizobium bacteria growing on the roots of leguminous plants, such as clover and soybeans, convert atmospheric nitrogen to nitrogen that is chemically bound in biomolecules. This nitrogen is converted to ammonium ion, NH, when plant residues and animal feces, urine, and carcasses undergo microbial decay. 

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