Among a set of frameshift mutagen (ICR-191; Polysciences, Inc.)-induced mutations that confer inability to grow anaerobically with N2O as the sole electron acceptor, one class was found that produced an inactive N2O reductase which lacked copper. All of these mutant strains failed to produce a 61,000-Mr protein located in the outer membrane. This protein, termed NosA, seems not to be responsible for bringing copper into the cell because the mutant strains and their parent were similarly sensitive to the copper content of the growth medium and no intermediate copper concentration in the medium permitted the mutant strains (nosA) to grow anaerobically with N2O as the sole electron acceptor. We conclude that NosA is necessary to insert copper into N2O reductase or to maintain it there.

The numbers and types of microorganisms on fresh rock cod fillets and fillets stored in air or in a modified atmosphere (MA; 80% CO2, 20% air) at 4°C were compared. Samples were analyzed after 0, 7, 14, and 21 days of storage. The isolation plates were incubated aerobically, anaerobically, or under MA at 4, 20, or 35°C. After 7 days of storage in air, the fillets were obviously spoiled and had a 3to 4-log cycle increase in microbial counts. Plate counts increased more slowly on MA-stored fillets. After 21 days, the counts on the latter had increased only 2 log cycles, and the fillets did not seem spoiled. The microbial flora changed greatly during MA storage. Only Lactobacillus spp. (70%) and an Aeromonas sp.like isolate (30%) were found on plates incubated aerobically at 4 and 20°C, and only Lactobacillus spp. was found on plates incubated aerobically and anaerobically at 35 and at 20°C under MA. Isolation plates incubated at 20°C in air gave the highest counts in the shortest incubation time and the greatest diversity of bacterial types recovered. No Vibrio parahaemolyticus, Staphylococcus aureus, or Clostridium botulinum type E were isolated from the fresh or MA-stored fillets.

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