Effects of Betaine on the Ultrastructure of Salt-Treated Escherichia Coli

Abstract

The ultrastructural changes have been studied in Escherichia coli 1130B-2ATCC (E. coli) grown on nutrient agar medium, medium + 0.8 M NaCl and medium + 0.8 M NaCl + 0.001 M betaine. Each dish was inoculated with 1027 bacteria and allowed to grow for 72 hours. Colony counts in the media was, medium alone (83), medium + NaCl was (18) and medium + NaCl + betaine was (48), indicating that nearly three times as many colonies grew in the presence of betaine in the NaCl medium, than those grown in the NaCl medium alone. Electron micrographs of sectioned E. coli cells grown on normal medium displayed a cell wall composed of outer membrane and cytoplasmic membrane enclosing a periplasmic space. The nucleoid was centrally located and contained fine DNA fibrils. Numerous ribosomes were present in the electron-dense cytoplasm. The cell division was achieved by septum formation. Sectioned cells grown on NaCl medium displayed many vesicles being pinched off from the cell surface. The outer membrane and the cytoplasmic membrane were disrupted at several sites, resulting in loss of cellular contents. The cytoplasm in some sections became electron-lucent, devoid of ribosome and contained dense bodies and membrane whorls. In other cells the cytoplasm appeared fragmented into small masses. In longitudinal sections of the cells the nucleoid material appeared in thick DNA fibrils, which in transverse sections was seen as a dark, round clump. The cell division was arrested, non-dividing cells were elongated and displayed aberrant mesosomes, vesicles and bulges. Sectioned cells grown on NaCl-betaine medium appeared normal. Their outer and cytoplasm membranes were intact and enclosed a periplasmic space. The nucleoid material appeared as fine DNA fibrils. The cytoplasm was electron-dense and rich in ribosomes. This study suggests that betaine acts as an effective osmoprotectant for E. coli offsetting NaCl-induced osmotic stress by maintaining the integrity and stability of its cell constituents.