Enhancing Effects of Carbon Dioxide on the Primary Isolation of Acid-Fast Bacilli in a Modified Lowenstein-Jensen Medium

Specimens inoculated on modified Lowenstein-Jensen medium were incubated aerobically and in an atmosphere of 8% CO₂. Sixteen per cent of the positive specimens grew Mycobacterium tuberculosis only after incubation in CO₂.     

DNA as the Intracellular Secondary Target for Antibacterial Action of Human Neutrophil Peptide-I Against Mycobacterium tuberculosis H37Ra

The secondary intracellular target of human neutrophil peptide-1 has been examined in M. tuberculosis H₃₇Ra. Binding studies with radioiodinated HNP-1 revealed biphasic equilibrium binding kinetics with respect to time. The major site of HNP-1 binding was found to be plasma membrane/cell wall whereas the cytosol appears to be a secondary site. Among the different macromolecules examined, maximum inhibition (75%) was observed in DNA biosynthesis during treatment with HNP-1. The interaction of HNP-1 with mycobacterial genomic DNA on the basis of gel retardation assay revealed HNP-1 binding to DNA. These results indicate that HNP-1 has DNA as the secondary intracellular target for antibacterial action against mycobacteria. Received: 25 October 2000/Accepted: 10 January 2001     

Growth of Bacteria in Inorganic Medium at Different Levels of Airborne Organic Substances

Invasion rates of airborne organic substances into sterile mineral medium were compared by using flasks closed with cotton stoppers, silicone stoppers, and screw caps with Teflon gaskets. The resulting increases of dissolved organic carbon were 0.5, 0.2, and 0 mg/liter per week, respectively. The compounds supported the growth of lake water bacteria and a strain of Pseudomonas fluorescens. Growth rates were correlated to the permeability of the stoppers used. The measured input of organic carbon in the sterile mineral medium is considered to be a minimum value for the actual contribution of organic compounds by the air. Multiplication rates of the bacteria suggest that the organisms prevent the escape of volatile organic substances from the medium by rapid utilization. The steady nutrient supply through the air should be considered in growth experiments with bacteria at low concentrations of nutrients.     

The Effect of Various Nitrogen Sources upon Heterocyst Formation in Anabaena Flos-Aquae A-37

Heterocysts are formed abundantly in cultures of Anabaena flos-aquaeA-37 which are fixing nitrogen. Fewer are formed in the presenceof NO₃^– ions, whereas none occurred in the presence ofNH₄⁺ ions. The results indicate that heterocysts may have arole in nitrogen metabolism.