Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Heike Bucking


bioinoculant, endophyte, phosphate, phosphate solubilizing, plant growth promoting, soil bacteria


Conservative models have shown that as populations rise, food production needs to double by 2050. Population increase and the green revolution have caused fertilizer inputs to increase since the 1960’s, increasing environmental issues and production costs. These intensive practices have led to degraded arable land and there has been an increase in urbanization meaning we need to make best use of the farming land that is available and ensure it is sustainable for future food production. Due to this, there has been a higher demand for research on more environmentally and economically friendly approaches to food production. Plant growth promoting bacteria have been a promising approach to more sustainable farming and have been shown to increase plant growth through characteristics such as; nitrogen fixation, plant hormone production, fungal suppression, and phosphate solubilization. It is estimated that only 0.1% of the phosphorus in the soil is in a soluble form, and approximately 80% of the phosphorus fertilizer applied gets bound in the soil and is not available to plants. Phosphate solubilizing bacteria can produce organic acids and phosphatase enzymes to solubilize soil phosphorus. Phosphate biofertilizers are one of the largest growing portions of the bioinoculant industry. In our research we have isolated and identified several potential plant growths promoting and phosphate solubilizing bacteria. In addition, we identified some of the specific mechanisms used to increase plant growth, as well as the mechanisms to solubilize inorganic phosphorus. Four novel isolates of the Oxalobacteraceae family were identified and characterized. Based on their phenotypic, morphological, and genomic analysis, three of the isolates are novel at the species level and one at the genus level. These isolates were cultured from agriculture and garden soils and have several genes that are considered plant growth promoting such as; nitrate reductase, urease, phosphatase, biotin production, decomposition on hydrogen peroxide, and biofilm biosynthesis. The four novel isolates are; Pseudoherbaspirillum sperare OM1, Massilia arenosa MC02, Massilia hortus ONC3, and Duganella callidus DN04. Seventy bacteria were cultured from corn tissue, rhizosphere, and loose root soil and were screened for phosphate solubilizing abilities. Of the eight isolates tested, three bacteria were able to solubilize the highest level of phosphate; Enterobacter cloacae (Tr3R3), Raoultella ornithinolytica (M2R1), and Kosakonia sp. (Tc3So2). Of these three isolates, Tr3R3 and Tc3So2 had the highest soybean root and shoot biomass, root architecture, and plant phosphorus concentrations. Organic acid production was measured through HPLC and the two isolates that produced the greatest amount of soluble P, also produced the greatest amount of succinic acid. Additionally, the two isolated that did not solubilize any P, similarly did not produce any succinic acid, concluding that the succinic acid was the mechanism used to solubilize the phosphate. Through these tests as well as additional plant growth promoting tests such as nitrogen fixation, indole acetic acid biosynthesis, and fungal suppression, we found that Tr3R3 and Tc3So2 are promising bioinoculants.

Library of Congress Subject Headings

Microbial inoculants.
Plant growth promoting substances.
Phosphates -- Solubility.
Growth (Plants)
Sustainable agriculture.



Number of Pages



South Dakota State University



Rights Statement

In Copyright