SOCIOBIOLOGICAL BEHAVIOUR OF Dictyostelium WILD ISOLATES.

MAY 25-JULY 25 1998

INDIAN INSTITUTE OF SCIENCE , BANGALORE

GUIDE:Dr.V.Nanjundiah

SUMMER FELLOWSHIP AND RAJIV GANDHI SCIENCE TALENT SEARCH FELLOWSHIP PROGRAMME OF JAWAHARLAL NEHRU CENTRE FOR ADVANCED SCIENTIFIC RESEARCH

Slime molds alternate between a unicellular and a multicellular phase of lifecycle.When food is scarce, freeliving single amoebae aggregate to form a multicellular migrating slug (typically 100000 amoebae).The slug culminates into a fruiting body consisting of a stalk composed of dead vacuolated cells supporting a mass of spores. I addressed the following questions:

Do different strains coaggregate in the wild?

If so,does each of them have a particular tendency for either prestalk or prespore formation?

Would the tendency for prestalk change if conditions favoured prespore formation or would they retain positional memory?

Strains used were from Mudumalai

D.macrocephalum 39.2Aii, 1.2Ai

D.purpureum 5.2Aii

D.discoideum NC4

Uncharacterized 50dc8(black and white sori); 46d2c1(black and white sori)

Spore forming efficiency was established for the strains 39.2Aii, 1.2Aii, 5.2Aii Mixing experiments were carried out with black and white sori forming uncharacterized strains in various ratios(B:W::1:1,1:2, 2:1,1:4, 4:1) to study their aggregation behaviour. Fluorescence Activated Cell Sorter was used to measure Autofluorescence, Forward scatter, Side scatter to characterize size and granularity and study variation in amoebae and spore populations. It was found that samples 46d2c1 black and 46d2c1 white when mixed yielded sori of only one color, either black or white. Samples 50dc8 black and white when mixed yielded all sori of a single intermediate brownish color. The FACS profile of the white and black sori forming different strains from the 46th and 50th hectares indicated spores of two extreme sizes,very large or very small. It was found that different strains do coaggregate and form chimaeric sori. Conclusions could not be made as they were not traced through the developmental pathway. The FACS profiles of D.macrocephalum and D.purpureum wild isolates indicated amoebae of two extreme sizes-very large or very small unlike the lab strain NC4 which had no such extremities in amoebae or spore sizes. These size differences seemed to be a characteristic of wild isolates. Autofluorescence was not observed for any sample. It would be interesting to find what adaptational benefits were conferred as a result of size.