Inhibition of microbial colonization of shipboard fuel systems

The aim of the investigation was to study the problem of colonization of shipboard fuel systems and to examine the effect of a number of environmental factors on microbial growth and survival in order to find potential preservative treatments. A variety of microbial species were isolated from samples taken from fuel storage tanks. Bacteria were more numerous than yeasts or fungi and most microorganisms were found at the fuel/water interface. 1he salinity, pH and phosphate concentration of some water bottoms were characteristic of sea water. Others were brackish, acidic and varied in phosphate content. Microorganisms were cultured under a number of environmental conditions. After prolonged incubation, the inoculum size had no effect on the final biomass of Cladosporium resinae but the time required to achieve the final mass decreased with increasing spore number. Undecane supported better growth of the fungus than diesel fuel and of four types of diesel fuel, two allowed more profuse growth. With sea water as the aqueous phase, a number of isolates were inhibited but the addition of nutrients allowed the development of many of the organisms. Agitation increased the growth of C. resinae on glucose but inhibited it on hydrocarbons. The optimum temperature fgr growth of C. resinae on surface culture lay between 25º C and 30º C and growth was evident at 5º C but not at 45º C. In aqueous suspension, 90% of spores were inactivated in around 60 hours at 45ºC and the same proportion of spores of C. resinae and Penicillium corylophilum were destroyed after about 30 seconds at 65ºC. The majority of bacteria and all yeasts in a water bottom sample were killed within 10 seconds at this temperature. An increase in the concentration of an organo-boron compound caused more rapid inactivation of C. resinae spores and raising the temperature from 25ºC to 45°C significantly enhanced the potency of the biocide.

Growth, sporulation and spore properties of bacillus stearothemophilus produced in chemically defined media

The nutritional requirements for the vegetative growth of B. stearothermophilus strains NCIB 8919, NCTC lO,OO3 (wild) were found to be DL-methionine, biotin, nicotinic acid, thiamin, glucose and mineral salts. Strains NCIB 8920 required in addition L-tryptophan. B. stearothermophilus NCTC lO,OO3 (mutant) grew in a medium containing only glucose and mineral salts. Separate chemically defined media for the growth of Bacillus stearothermophilus strains NCIB 8919, 8920, NCTC lO,OO3 (wild) and NCTC lO,OO3 (mutant) were developed. Optimally aerated culture of B. stearothermonhilus NCTC lO,OO3(mutant) required 1.0 x 10-4 M. Mn2+ and 2.4 x 10-3 M. glutamic acid for optimal sporulation. Specific nutrient depletion of growth affected percentage sporulation. Spore suspensions of B. stearothermophilus NCTC 10,003 (mutant) were prepared from media in which sulphate (SO4-), nitrogen (N-),phosphate (Po4-), carbon (C-), magnesium-carbon simultaneously (Ng-C-) depleted growth. The heat resistance, dormancy and chemistry of these spores varied considerably. B. stearothermophilus NCTC 10,003 10,00310,00(mutant) spores prepared from carbon depleted cultures containing high and low concentrations of calcium, iron or manganese showed variations in heat resistance,dormancy and chemical composition. Progressive increase in the concentration of medium calciumfrom 1.0 X 10-5  M to 1.4 X 10-4 M. progressively increased theheat resistance of B. stearothermophilus NCTC 10,003 (mutant) spores prepared from nitrogen depleted cultures (N-). The thermodynamic functions for germination rate, magnesium and manganese release of N- and SO4- spores were within the range expected of enzymic reactions. The thermodynamic functions for the breaking of dormancy in SO4- spores and that for the release of D.P.A. were identical. Sublethal heating of SO4- spores (96.5°C and below) induced dormancy in these spores, whereas heating above 96.5°C gave rise to heat activation. Pooled results of the chemical analyses of all spore types studied showed that the concentration of D.P.A. and calcium were positively related to heat resistance whereas magnesium concentration and Mg/Ca molar ratio were inversely proportional to heat resistance.