[Ultrastructure of the cell surface of heteromorphic Nostoc muscorum CALU 304 cocultured with Rauwolfia tissue]

The ultrastructure of the heteromorphic cells (HMCs) of the cyanobacterium Nostoc muscorum CALU 304 grown in pure culture, monoculture, and a mixed culture with the Rauwolfia callus tissue was studied. The comparative analysis of the cell surface of HMCs, the frequency of the generation of cell forms with defective cell walls (DCWFs), including protoplasts and spheroplasts, and the peculiarities of the cell surface ultrastructure under different growth conditions showed that, in the early terms of mixed incubation, the callus tissue acts to preserve the existing cyanobacterial DCWFs, but begins to promote their formation in the later incubation terms. DCWFs exhibited an integrity of their protoplasm and were metabolically active. It is suggested that structural alterations in the rigid layer of the cell wall may be due to the activation of the murolytic enzymes of cyanobacteria and the profound rearrangement of their peptidoglycan metabolism caused by the Rauwolfia metabolites diffused through the medium. These metabolites may also interfere with the functioning of the universal cell division protein of bacteria, FtsZ. In general, the Rauwolfia callus tissue promoted the unbalanced growth of the cyanobacterium N. muscorum CALU 304 and favored its viability in the mixed culture. The long-term incubation of the Rauwolfia tissue with the N. muscorum CALU 304 cells led to their transformation to L-forms.