The growth of bacteria is often enhanced by addition of carbon materials such as graphite or activated charcoal to the growth medium. In this work, bacterial strains that strictly require such carbon materials under the ordinarily lethal stress caused by high concentrations of salt were isolated. The organisms were gram-positive, spore-forming, sugar-nonfermenting aerobic bacilli and were provisionally designated ''Bacillus carbophilus'' Kasumi after examination of their phenotypic traits. The growth-and germination-promoting effects of graphite and activated charcoal were demonstrated either quantitatively on agar plates containing fine crystals of the carbon materials mixed with a nonpermissive growth medium or qualitatively on agar plates on nonpermissive growth media half-covered with fine carbon particles. Further experiments demonstrated a novel feature of the phenomenon; i.e., the ability to induce colony formation on the nonpermissive plate was transmissible through the air, as well as through plastic or glass barriers. The mechanism probably involves transmission of physical signals regulating cell growth.The unique biological effects of carbon materials, such as graphite and activated charcoal, have frequently been recognized: e.g., charcoal powders are often applied to the soil to enhance plant growth or used to facilitate the proliferation of bacteria such as Neisseria gonorrhoeae (4), Haemophilus pertussis (7), and Legionella pneumophila (3); artificial cardiac valves made of carbon displayed antithrombogenecity (1, 5); and carbon tooth implants displayed a favorable affinity to gingival tissue (10). It seems to be generally accepted that these carbon materials act indirectly on living organisms, e.g., by adsorbing inhibitory substances from the medium. We report here that carbon exerts a novel effect on the proliferation of at least some bacteria, involving an unexpected mechanism.
MATERIALS AND METHODSCarbon and other materials. Graphite preparations were provided by the Toyo Carbon Co., Osaka, Japan (graphites A to C), and the Mitsubishi Pencil Co., Tokyo, Japan (graphites 1 to 4). Their sources and properties are listed in Table 1. Two activated-charcoal preparations, one washed with HCl and the other washed with HCl and then neutralized, were Sigma products. Aluminum oxide (Wako Pure Chemicals, Kyoto, Japan) and levigated alumina (Norton Co., Worcester, Mich.) were commercial products. Glass powders were prepared by grinding microscope slide coverslips in a ceramic mortar, washed repeatedly with water, and sterilized by autoclaving. Carbon materials scattered on agar plates were used after exhaustive sterilization by heating at about 700ЊC for 1 min on a gas burner. In other cases, they were mixed with nutrient agar and autoclaved at 120ЊC for 15 min.Bacteria and growth conditions. Isolation and preliminary characterization of bacteria with high graphite requirements are described below. These are Bacillus strains and are maintained in our collections (Tokai University and Fujisawa Pharmaceutic...
