Assessing the effectiveness of low-pressure ultraviolet light for inactivating Mycobacterium avium complex (MAC) micro-organisms.

AIMS: To assess low-pressure ultraviolet light (LP-UV) inactivation kinetics of Mycobacterium avium complex (MAC) strains in a water matrix using collimated beam apparatus. METHODS AND RESULTS: Strains of M. avium (n = 3) and Mycobacterium intracellulare (n = 2) were exposed to LP-UV, and log(10) inactivation and inactivation kinetics were evaluated. All strains exhibited greater than 4 log(10) inactivation at fluences of less than 20 mJ cm(-2). Repair potential was evaluated using one M. avium strain. Light repair was evaluated by simultaneous exposure using visible and LP-UV irradiation. Dark repair was evaluated by incubating UV-exposed organisms in the dark for 4 h. The isolate did not exhibit light or dark repair activity. CONCLUSIONS: Results indicate that MAC organisms are readily inactivated at UV fluences typically used in drinking water treatment. Differences in activation kinetics were small but statistically significant between some tested isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: Results provide LP-UV inactivation kinetics for isolates from the relatively resistant MAC. Although UV inactivation of Mycobacterium species have been reported previously, data collected in this effort are comparable with recent UV inactivation research efforts performed in a similar manner. Data were assessed using a rigorous statistical approach and were useful towards modelling efforts.

Sphingomonas sp. strain Lep1: an aerobic degrader of 4-methylquinoline.

Strain Lep1, isolated from a bacterial consortium capable of aerobic degradation of 4-methylquinoline (4-MQ), was chosen for further characterization as it was the only member of the consortium able to grow on 4-MQ in pure culture. Lep1 was identified as a Sphingomonas sp. based on phylogenetic analysis of 16S rDNA. Furthermore, the presence of sphingolipids and 2-hydroxy fatty acids in the membrane, and a 63% G + C ratio supports the placement of Lep1 in this genus. Additional genetic, physiological, and ecological characterization of bacteria such as Lep1 will allow for the potential exploitation of degradative strains for purposes of bioremediation of contaminated soils.

Aerobic biodegradation of 4-methylquinoline by a soil bacterium.

Methylquinolines and related N-heterocyclic aromatic compounds are common contaminants associated with the use of hydrocarbons in both coal gasification and wood treatment processes. These compounds have been found in groundwater, and many are known mutagens. A stable, five-member bacterial consortium able to degrade 4-methylquinoline was established by selective enrichment using soil collected from an abandoned coal gasification site. The consortium was maintained for 5 years by serial transfer in a medium containing 4-methylquinoline. A gram-negative soil bacterium, strain Lep1, was isolated from the consortium and shown to utilize 4-methylquinoline as a source of carbon and energy during growth in liquid medium. A time course experiment demonstrated that both the isolate Lep1 and the consortium containing Lep1 were able to degrade 4-methylquinoline under aerobic conditions. Complete degradation of 4-methylquinoline by either strain Lep1 alone or the consortium was characterized by the production and eventual disappearance of 2-hydroxy-4-methylquinoline, followed by the appearance and persistence of a second metabolite tentatively identified as a hydroxy-4-methylcoumarin. Currently, there is no indication that 4-methylquinoline degradation proceeds differently in the consortium culture compared with Lep1 alone. This is the first report of 4-methylquinoline biodegradation under aerobic conditions.