Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Pseudomonas syringae causes freezing of supercooled water at temperatures close to 0{dollar}\sp\circ{dollar}C. In this study, the growth kinetics and ice nucleation activity (INA) of the bacterium P. syringae cit 7 were investigated under a variety of culture conditions as well as in batch and continuous bioreactors. The "drop freezing assay" technique used for measurement of INA was first investigated and the effect of several variables on this assay was examined. When P. syringae cit 7 was cultured aerobically in a medium consisting of sucrose, peptone, K{dollar}\sb2{dollar}HPO{dollar}\sb4{dollar}, KH{dollar}\sb2{dollar}PO{dollar}\sb4{dollar}, and MgSO{dollar}\sb4\cdot{dollar}7H{dollar}\sb2{dollar}O (pH 7.0) at 25{dollar}\sp\circ{dollar}C for 48 h, the highest INA was detected at {dollar}-{dollar}2.5{dollar}\sp\circ{dollar}C. The INA expressed by the bacteria was independent of cooling rate at cooling rates less than 0.2{dollar}\sp\circ{dollar}C/min. Cell growth at temperatures exceeding 25{dollar}\sp\circ{dollar}C led to a decrease in INA expression of cells. Similarly, cell growth at pH of 8.0 also decreased the INA of the bacteria. Microaerophylic conditions during cell growth also decreased INA in the P. syringae cit 7 bacteria. In a 1 L bioreactor, the optimum cell growth temperature P. syringae cit 7 was found to be 28{dollar}\sp\circ{dollar}C. INA of the cells developed in the lag as well as log phase of growth. The maximum INA in the bioreactor was obtained at the end of the exponential phase of growth at each temperature investigated. In the bioreactor growth at temperatures greater than 25{dollar}\sp\circ{dollar}C led to a significant decrease in INA. Batch cell growth kinetics in the 15 L bioreactor followed a similar trend to the 1 L bioreactor.;Under continuous cultivation in a 1 L bioreactor at 25{dollar}\sp\circ{dollar}C, and pH 7.0, the INA of P. syringae decreased with an increase in dilution rate. A maximum specific growth rate of 0.08 h{dollar}\sp{lcub}-1{rcub}{dollar}, and a K{dollar}\sb{lcub}\rm s{rcub}{dollar} of 0.21 g/L were obtained under these conditions. Under continuous conditions, cell productivity reached a maximum at a dilution rate of 0.054 h{dollar}\sp{lcub}-1{rcub}{dollar} and then continuously decreased. A mechanistic, unstructured model describing the batch growth kinetics in the 1 L bioreactor was found to adequately represent the growth and INA in the bioreactor. The results of this investigation can be applied towards large scale production of P. syringae bacteria for snow making applications.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.