aerogenes bacteria. The plating efficiency of cyst spores was 70%, similar to that of 17-AAG side effects spores collected from fruiting bodies on filters, which was 66%. Thus, terminal cell differentiation occurred in radially symmetrical fash ion in the absence of the normal morphogenetic move ments of culmination. This contrasts with the slug like elongated and linearly polarized aggregates formed when cells were agitated in high O2. The radially polar ized organization may result from a more uniform envir onment presented by the static setting in which polarizing gradients of O2 or NH3 fail to form. Under 21% O2, stalk cells and spores were rarely observed in the less compacted aggregates that form under these conditions. When present they occurred as clusters or single cells.

At 40% O2, larger aggregates were formed but they lacked dense cores observed at higher O2 levels. These cyst like aggregates possessed a stalk cell cortex but their interior cells pro duced few spores, as visualized after squashing. Though spores were not detected in this example, variable numbers were observed over the 5 in dependent trials as quantitated in Figure 4C. The vari ation suggests that 40% O2 is close to the threshold required for sporulation whose exact value is likely influ enced by other factors, as observed for culmination. To address the differentiation status of cells at the lower O2 levels, extracts were Western blotted for the spore coat precursor proteins SP85, SP96 and SP75 that are markers of prespore cell differentiation. Whereas all 3 glycoproteins appeared in Ax3 cells by 24 h at 70% O2, negligible expression occurred at 20% after 3 d.

Thus increasing O2 levels were required for tight aggregate formation, terminal stalk cell differenti ation, and differentiation of the interior prespore cells into spores. It is likely that metabolic O2 consumption results in intracyst hypoxia in these unstirred cultures which, in the submerged state, is not adequately replen ished by O2 diffusion. The finding that elevated O2 ten sion in the atmosphere above the medium can rescue terminal differentiation indicates that O2 availability is the limiting factor for terminal cell differentiation in this setting. It is not evident whether the higher O2 level required for spore compared to stalk cell differentiation reflects a higher O2 threshold requirement for spore dif ferentiation or lower O2 in the aggregate centers.

Requirement of PhyA for sporulation in submerged conditions A previously described mutant strain disrupted Batimastat at its phyA locus was analyzed to determine the involve ment of Skp1 prolyl 4 hydroxylation in submerged de velopment. phyA cells formed cyst like structures at 40 100% O2 with outer layers of differentiated stalk cells, similar to the normal Ax3 strain.