Giardia lamblia cysts were harvested from Mongolian gerbils and exposed to free chlorine in buffered water at pH 5, 7, and 9 at 15°C. The contact times required to obtain a 2-log reduction in cyst survival (i.e., a 99% kill) were interpolated from survival curves generated at fixed concentrations of chlorine in the range of 0.25 to about 16 mg/liter. Concentration-time (C-t') products for 99% inactivation ranged from about 120 to nearly 1,500 mg-min/liter. These values are higher than those reported previously for free chlorine using G. lamblia cysts from infected humans. The cysts isolated from gerbils, as with other Giardia cysts, were unusually sensitive to chlorine in alkaline solutions.

No abstract

The obligate halophilic member of Rhodospirillaceae, Rhodospirillum salexigens, does not contain lipopolysaccharide in its thin and delicate gram-negative type cell wall. Major constituents are protein (approximately 70% of dry weight) and peptidoglycan (murein).

A cell surface protein (Mr 68,000) of the moderately but obligately halophilic phototrophic bacterium Rhodospirillum salexigens was identified by two independent methods: first, by labeling the cell surface with radioactive iodine and lactoperoxidase, and second, by washing cells in 30% sucrose to remove proteins attached to the cell surface by ionic bonds. The identified protein very likely represents the outermost layer of the cell envelope of R. salexigens as observed by electron microscopy. The protein was isolated. Its isoelectric point was determined to be 4.4; the excess of acidic over basic amino acids was found to be 18.3 mol %; and its average hydrophobicity was 2.26 kJ per residue. Although extremely halophilic bacteria and their cell walls have been the focus of extensive work (for a review, see reference 10), moderately halophilic bacteria have not been studied in such detail yet. The latter are found in all