The coliform bacterial population in the Grand Forks, N.Dak. sewage system was examined for multipleantibiotic-resistant organisms over a 1-year period. Multiple-antibiotic-resistant coliforms were found to be common in the sewage, and their numbers remained fairly constant relative to the total coliform population throughout the year. Resistance to kanamycin, tetracycline, and ampicillin was found to be transferable at variable rates. Transfer rates were found to be temperature sensitive and were optimal at 35°C. Although 75 % of the multiple-antibiotic-resistant coliforms were capable of transferring resistance at some level, only 25% were capable of transferring resistance at rates greater than 1o-3 transconjugants per initial donor.

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The ecology of purple sulfur bacteria in a sewage oxidation lagoon was investigated. Chemical changes in the lagoon were investigated by monitoring biochemical oxygen demand (BOD 5 ), sulfide, sulfate, phosphate, total carbohydrates, volatile acids, alkalinity, and p H. Lagoon water temperatures were observed daily. Microbial ecological relationships were deduced by enumerating coliforms, total bacteria other than anaerobes [Tryptone Glucose Extract (TGE) agar], methane formers such as Methanobacterium formicicum , sulfate reducers, purple sulfur bacteria, and algae. Finally, two strains of purple sulfur bacteria were characterized. Two populations, purple sulfur bacteria and total bacteria (TGE agar), reached maximal concentrations in the warmest part of the 1967 summer. Purple sulfur bacteria reached maximal numbers as concentrations of sulfide and volatile acids were depleted, whereas carbohydrates and alkalinity remained unchanged. Low sulfate levels, which were not limiting for sulfate reducers, may be attributable to storage of sulfur within purple sulfur bacteria. No biological, chemical, or physical agent was linked to the removal of coliforms. The increase of algae in the late summer of 1967 may have been related to the low organic content of the lagoon during this period. Although lagoon p H (7.7 to 8.2) was favorable for purple sulfur bacterial growth, temperatures and sulfides were not optimal in the lagoon for these organisms. Chromatium vinosum and Thiocapsa floridana (the predominant lagoon purple sulfur organism in 1967 and 1968) utilized certain carbohydrates, amino acids, volatile acids, and Krebs cycle intermediates. Also purple sulfur bacteria lowered BOD levels as demonstrated by the growth of T. floridana in sterilized sewage.

One of the striking advances of modern bacterial cytology has been the development of methods for the isolation and purification of the major structural components of the bacterial cell. These methods have been used with notable success in characterizing nmuch of the physical,