Dispelling the “Nocardia amarae” myth: a phylogenetic and phenotypic study of mycolic acid-containing actinomycetes isolated from activated sludge foam

Right-angle branched filaments and rods micromanipulated from activated sludge foam and mixed liquor were identified as putatively novel members of the genera Gordonia, Mycobacterium and Rhodococcus using a combination of chemical, molecular and morphological data. Pyrolysis mass spectrometric analyses of gordoniae isolated in both the present and a previous study revealed pyro-groups, distinct from validly described Gordonia species, which could be equated with those based on morphological properties and 16S rDNA data. Putative gordoniae assigned to one of these groups were found to be closely related to strains currently identified as “Rhodococcus australis”. These strains were also found to have properties consistent with their classification in the genus Gordonia. The results of this study highlight the limitations of the microscopic approach to filament identification and cast further doubt on the view that foaming can be attributed to members of one or a few Nocardia species.

Gordona scum suppression mechanism of ozone added in wastewater treatment plants

In order to prevent the scum generation due to Gordona (Nocardia) amarae, experiments were made to add ozone in the aeration tank from 1990 to 1994, and scum suppression effects, sludge settleability improvement effects, etc. were reported. The studies made so far did not clarify the scum suppression mechanism of added ozone. Based on the measurements of the number of Gordona, mycolic acid, etc., an attempt was made to investigate this mechanism. By adding ozone, the number of Gordona was suppressed in general to below 1 × 105 CFU/mg-SS. In the presence of mycolic acid produced by Gordona amarae at a rate of about 178-236 μg in 1g activated sludge, no scum generation was seen. Within an experimental range of ozone added at a rate below 3 mg/l, it was considered that the scum suppression effect was due more to the decomposition of mycolic acid, which is a metabolite of Gordona amarae, than to the effect of the number of Gordona amarae being reduced by the disinfectant action of ozone.