This discussion forum focuses on the nature of micro-organisms and other organisms that are ice nucleators (can catalyze freezing of supercooled water) and their role in cloud processes and precipitation.


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Role and evolution of the IN gene?

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1 Role and evolution of the IN gene? on Fri Dec 05, 2008 8:43 am

I find it intriguing that it’s hard to define the principal ecological function of such a highly evolved protein. Could it actually have multiple functions or do we lack insight?

Hirano and Upper (2000) wrote “there is no clear selection for destroying the leaf habitat. For most organisms, habitat destruction is regarded as highly unfavorable…..the bacteria reward themselves for success [as colonists] by destroying their habitat! Is this not paradoxical?” But could IN bacteria be protecting their property by triggering high temp freezing? Once nucleation occurs freezing travels extensively throughout the xylem. The ice demands water and sucks it out of cell’s protoplasts, protecting them. If this happens slowly the cells survive. I notice that on grapevines tissue near the nucleation point and adjacent to the xylem freezes but leaves and mesophyll further away does not, and then the plant re-shoots vigorously, investing in more leaves and not fruit.

The diversity of IN alleles suggests they have been evolving for hundreds of millions of years. So what did they do in the former – the real – world? Before our patchwork quilt world. Pangaea is perhaps where the IN gene evolved. Pangaea had dinosaurs, vast ecosystems and deserts (with OM-enriched dust floating over them). How important were bioaerosols in that world? Was it the same repertoire of forces that operate in a vineyard or a field of beans?

Where do the INA bugs call home now? If the 10^9 nuclei (active at -10 C) per gram of leaf litter in Canada and Russia, found by Russ Schnell and Gabor Vali, are INA bacteria then isn’t this their real home, and the IN protein is for water gathering or for freezing leaf litter and its decomposer community (freeze/thaw cycles stimulate decomposition in soil).

Tom Hill
tchill@unimelb.edu.au

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2 Re: Role and evolution of the IN gene? on Mon Dec 15, 2008 12:52 am

Just how old is the gene for the INA protein? Is it hundreds of millions of years, or even more? How would we determine this and what would be the error in the estimation? Perhaps this gene conferred a function in the lives of bacteria with plants. But, if we consider bacteria over the full evolutionary time scale, is it possible that this gene evolved firstly for other functions? The first single-celled life forms on Earth (bacteria) emerged 3500 My ago. The beginning of oxygen accumulation on our planet, permitting the emergence of aerobic bacteria, occurred 2200 My ago. The earliest eukaryotes appeared about 3000 to 2500 My ago, however higher plants did not begin their appearance on Earth until about 700 – 500 My ago. Is there anything in the lives of aerobic bacteria that could have been happening in the 1500 My or so before the emergence of higher plants where ice nucleation activity could have played a role?

Cindy Morris

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