**2. Nitrogen supply by soybean cultivation**

### **2.1. Nitrogen fixing bacteria**

N2 is fixed by nitrogen fixing bacteria in the soil environment [14-17]. These bacteria convert N2 to NH4 + . The biological reduction of atmospheric N2 to NH4 <sup>+</sup> (nitrogen fixation) provides about 65% of the biosphere's available nitrogen [18].

As long ago as 1890, a nitrogen fixing bacteria was isolated from a root nodule and identi‐ fied as *Rhizobium leguminosarum* [19, 20]. Shortly after this, *Clostridium pasteurianum* and *Azo‐ tobacter* sp. were also isolated as nitrogen fixing bacteria in the soil environment [21-23]. Now, more than 100 genera have been isolated and identified as nitrogen fixing bacteria. Among them, genera *Rhizobium, Bradyrhizobium, Azorhizobium,* and *Frankia* lead to the for‐ mation of root-nodules in legumes [16].

Nitrogenase (EC 1.18.6.1) from nitrogen fixing bacteria catalyzes N2 to NH4 + (N2 + 8H2 + 8e- + 16ATP + 16H2O → 2NH3 + H2 + 16ADP + 16Pi). NH4 + is further converted to NO2 and NO3 by ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB).

**Figure 1.** Soybean root nodule

### **2.2. Relationship between nitrogen fixing bacteria and soybean cultivation**

purified and utilized as medicines for hypotension, rheumatism, and cholesterol control

This chapter explains how soybean cultivation and soybean protein are nitrogen suppliers

N2 is fixed by nitrogen fixing bacteria in the soil environment [14-17]. These bacteria convert

As long ago as 1890, a nitrogen fixing bacteria was isolated from a root nodule and identi‐ fied as *Rhizobium leguminosarum* [19, 20]. Shortly after this, *Clostridium pasteurianum* and *Azo‐ tobacter* sp. were also isolated as nitrogen fixing bacteria in the soil environment [21-23]. Now, more than 100 genera have been isolated and identified as nitrogen fixing bacteria. Among them, genera *Rhizobium, Bradyrhizobium, Azorhizobium,* and *Frankia* lead to the for‐

+

<sup>+</sup> (nitrogen fixation) provides

+

is further converted to NO2

(N2 + 8H2 + 8e-

and NO3


+


. The biological reduction of atmospheric N2 to NH4

Nitrogenase (EC 1.18.6.1) from nitrogen fixing bacteria catalyzes N2 to NH4

by ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB).

[11-13]. The bioactive peptides of soybean protein have also been investigated [5, 6].

A Comprehensive Survey of International Soybean Research - Genetics, Physiology, Agronomy and Nitrogen

and describes the production of novel bioactive peptides from soybean and legumes.

**2. Nitrogen supply by soybean cultivation**

about 65% of the biosphere's available nitrogen [18].

16ATP + 16H2O → 2NH3 + H2 + 16ADP + 16Pi). NH4

mation of root-nodules in legumes [16].

**2.1. Nitrogen fixing bacteria**

+

**Figure 1.** Soybean root nodule

N2 to NH4

Relationships

50

The roots of soybean secrete flavonoids and enhance the growth of nitrogen fixing bacteria around the root [24]. The nitrogen fixing bacteria infect the soybean root, and the root-nod‐ ule is formed. Bacteroids in the root-nodule fix and provide nitrogen from the air [25]. *Bra‐ dyrhizobium japonicum, B. elkanii, B. lianigense,* and *Sinorhizobium fredii* have been identified as the root-nodule forming bacteria in soybean cultivation [16, 26, 27].

The change in soil microbial diversity after soybean cultivation has been analyzed by PCR-DGGE. Root-nodules were shown to be formed and specific bacteria were increased during cultivation (Figures 1 and 2) but not the total number of bacteria in the soil. Soybean cultiva‐ tion caused nitrogen accumulation in the soil environment.

**Figure 2.** PCR-DGGE profiles of soybean cultivated soil, 1: Before cultivation, 2: after cultivation.
