Effect of different commercial agar preparations on the inhibitory activities of phenols

OUP accepted manuscript

Ammonia-oxidising archaea (AOA) are environmentally important microorganisms involved in the biogeochemical cycling of nitrogen. Routine cultivation of AOA is exclusively performed in liquid cultures and reports on their growth on solid medium are scarce. The ability to grow AOA on solid medium would be beneficial for not only the purification of enrichment cultures but also for developing genetic tools. The aim of this study was to develop a reliable method for growing individual colonies from AOA cultures on solid medium. Three phylogenetically distinct AOA strains were tested: ‘Candidatus Nitrosocosmicus franklandus C13’, Nitrososphaera viennensis EN76 and ‘Candidatus Nitrosotalea sinensis Nd2’. Of the gelling agents tested, agar and Bacto-agar severely inhibited growth of all three strains. In contrast, both ‘Ca. N. franklandus C13’ and N. viennensis EN76 tolerated Phytagel™ while the acidophilic ‘Ca. N. sinensis Nd2’ was completely inhibited. Based on these observations, we developed a Liquid-Solid (LS) method that involves immobilising cells in Phytagel™ and overlaying with liquid medium. This approach resulted in the development of visible distinct colonies from ‘Ca. N. franklandus C13’ and N. viennensis EN76 cultures and lays the groundwork for the genetic manipulation of this group of microorganisms.

Identification of a component of crystalline egg albumin bactericidal for thermophilic aerobic sporeformers

During an investigation of the effect of basic and acidic proteins on the growth of thermophilic aerobic sporeformers, crystalline egg albumin was found to be strongly bactericidal. This finding was uncharacteristic of acidic proteins. The bactericidal fraction was heat sensitive and separated from the non-bactericidal albumin fraction during gel filtration on Sephadex G-75. Cells of Micrococcus lysodeikticus and Bacillus stearothermophilus were lysed rapidly by the bactericidal component, leading to its tentative identification as lysozyme. The bactericidal substance possessed an electrophoretic mobility on polyacrylamide gel containing sodium dodecyl sulfate identical to that of crystalline egg white lysozyme. Users of crystalline egg albumin are cautioned that commerical preparations may be contaminated with lysozyme. Destruction of the thermophilic aerobes by lysozyme should be considered when performing counts on egg products.