Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Dairy and Food Science

First Advisor

Srinivas Janaswamy


Polysaccharides, Sodium alginate, κ-carrageenan, Beads, Biological Nitrogen Fixation


Nitrogen is a major limiting factor for crop production. Its primary source is the addition of inorganic nitrogen (ammonia or nitrate) fertilizer, which is not sustainable for continually boosting crop yield and food production. Toward this end, Biological Nitrogen Fixation (BNF) is an efficient alternative. Legumes are capable of BNF but designing and developing BNF traits transferrable to cereal crops and naturally generating ammonia is a long-sought goal. This study explored the use of non-toxic, biocompatible, and biodegradable polysaccharides alginate and κ-carrageenan to develop beads assembly and to encapsulate free-living nitrogen-fixing diazotrophs Azospirillum brasilense Sp7 and Herbaspirillum seropedicae Z152 for nitrogenase activity and nitrogen fixation. Alginate beads have been prepared in the presence of divalent and trivalent (Ca2+, Sr2+, Zn2+, Ni2+, Cu2+, and Al3+) cations and κ-carrageenan beads with K+ to shape as root nodular structure. Depending on the type of polymer and the crosslinked cation, the beads biodegrade over six weeks to three months. In wet conditions, these beads provide an oxygen-reduced environment, ranging from 1.4 ± 0.41 to 5.38 ±1.07 nmol/bead, demonstrating their viability to protect nitrogenase integrity. However, results suggest that only Ca2+ and Sr2+-alginate beads could endure diazotroph viability and facilitate the BNF. The A. brasilense Sp7 and H. seropedicae Z152 demonstrated a maximum nitrogenase activity of 1.76±0.31 and 2.25±0.39 Å mol. C2H2 h-1. million CFU-1 in Ca2+-alginate beads. The nitrogenase potential of A. brasilense Sp7 loaded beads was unaffected by sugars inclusion while that with H. seropedicae Z152 increased with the added energy element. This study successfully established the polysaccharide bead's potential to preserve nitrogen-fixing bacteria and aid in nitrogenase activity. The outcome is deemed to open a new window of opportunities for nitrogen nutrition in crops, mainly cereal crops.


South Dakota State University



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