Role of the dominant phototropic bacterium in anaerobic swine waste lagoons, Rhodobacter sp. PS9, in odor remediation

Temporal pigmentation changes in anaerobic swine waste lagoons were investigated during 4 year period. One commonly observed event in anaerobic swine waste lagoons is the development of purple color associated with the apparent reduction of odor intensity in late summer. The major purple phototrophic bacteria responsible for this color change and corresponding reduction in odor were isolated. Morphological, physiological, and phylogenetic characterization identified a predominant phototrophic bacterium as a new strain of Rhodobacter, designated Rhodobacter sp. PS9. Rhodobacter sp. PS9 is capable of photoheterotrophic growth on various organic compounds including all of the characteristic volatile organic compounds (VOC) responsible for the odor associated with swine production facilities. Seasonal variations of airborne VOCs emitted from waste lagoons also showed a 80--93% decrease in the concentration of VOC during the photosynthetic bloom. During the height of the bloom the Rhodobacter sp. PS9 population accounted for 9.6% of the total community and up to 27.0% of the eubacterial community structure. Additional observations based on seasonal variations of meteorological, biological and chemical parameters suggested the photosynthetic bloom of Rhodobacter sp. PS9 correlated with the water temperature and the organic loading rate of waste lagoon.