Ice-nucleating bacteria

Compare the freezing points of distilled water and distilled water containing ice-nucleating bacteria. 

Epiphytic ice nucleating bacteria provide an ideal system for studying the feasibility of "sibling competition". All the above conditions are thought to be met, except that no. 5 is demonstrated... 

A new approach to study root exudation of distinct compounds in soil-grown plants uses inoculation of roots with genetically engineered reporter bacteria, which are able to indicate the presence of particular compounds by indicator reactions, such as production of ice-nucleation proteins. This technique has been employed to detect the release of amino acids from roots of soil-grown A vena harbata (56). 

A technique utilizing genetically modified bacteria to report the presence of particular compounds in soil has also been developed (37). These bacteria respond to the presence of specific compounds in their environment by producing ice-nucleation proteins that enter into cell membranes, enabling cells to be detected by means of a droplet freezing assay. The presence of trytophan in 1-10 i molar concentrations has been detected using reporter bacteria in a study examining loss of amino acids from roots of Avena barbata into soil (38). 

Burke, M. Lindow, S. E. Surface properties and size of the ice nucleation of active bacteria Theoretical considerations. Cryobiology 27, p. 80-84, Copyright 1990 by Academic Press Inc. 1990... 

Certain strains of bacteria can competitively exclude other strains. Lindow (117) found that Ice (ice nucleation-active) populations of Pseudomonas syringae on corn plants Zea mays L.) were reduced by prior colonization of the leaves by Ice strains (ice nuleation-deficient). Interestingly, the total bacterial population was not affected by the prior inoculation of Ice strains (117). For these reasons, Lindow (117) concluded that the antagonism between these strains resulted from competitive exclusion of new arrivals to an occupied niche rather than competitive displacement. As the carrying capacity of leaf surfaces for bacteria is low relative to other plant habitats, particularly roots (101), preemptive colonization by one strain may be sufficient to reduce the population size of similar strains. The importance of competition for space among naturally colonizing microbes remains unknown. 

Proteins from certain bacteria are ice nucleators (Wolber et ai, 1986). An AFGP inhibits this nucleation, apparently by binding to the bacterial protein. 

Ice-nucleation active bacteria. This was the first microbial product of biotechnology for which approval of field tests was requested. This has resulted in a long court battle with no final conclusion to date. After 241 experiments, expenditures of 750,000, and five man-years of research, Advanced Genetic Sciences has not yet convinced regulators and the public that their modified Pseudomonas... 

Figure 1. Spectrum of ice nucleation frequency displayed by a genetically homogeneous population of bacteria coli strain...

The legal aspects of using ice nucleation deficient bacteria for frost protection are responsible for the attention accorded to this research by the popular media. Therefore it seems appropriate to provide a scientists perspective on these Issues and on the regulatory process as it applies to deliberate release experiments. 

Many of the outstanding problems in this field are of great importance to natural science. For example, the formation of ice in interstellar space remains to be explored. Certain bacteria that we find in plants have the unique ability to initiate ice nucleation at as high a temperature as -1 °C. How they perform this task is also shrouded in mystery. It is really interesting to find the existence of such a large number of fascinating problems in the area of water freezing. 

---