Effects of pH on Biomass, Geosmin, and 2-Methylisoborneol Production and Cellular Activity by Streptomyces luridiscabiei Isolated from a Rainbow Trout Recirculating Aquaculture System - Abstract
Rainbow trout (Oncorhynchus mykiss) grown in recirculating aquaculture systems (RAS) can acquire “earthy” and “musty” taints due to bioaccumulation of geosmin and 2-methyisoborneol (MIB), respectively, in the fish flesh and will result in an unmarketable product. Certain species of actinomycetes produce these compounds, and Streptomyces luridiscabiei was previously determined to be a contributor to geosmin and MIB presence in the RAS. In this study, the effects of pH on growth (dry-weight biomass), geosmin and MIB production (solid phase microextraction and gas chromatograph-mass spectrometer), and cellular activity (adenosine 5’-triphosphate via luminometer) by S. luridiscabiei were determined from cultures of S. luridiscabiei grown at different pH (0.5 increments from pH 6.0 to 9.0) over a 7-day period. There was not a dramatic difference in growth by S. luridiscabiei at different pH, with significantly (P < 0.05) highest biomass production on day 7 at pH 7.5. Cellular activity was significantly (P < 0.05) higher at pH 7.0 on day 7. Significantly (P < 0.05) higher amounts of geosmin and MIB were produced at pH 7.5 and 8.0. Results indicate that a large difference in the growth of S. luridiscabiei in the RAS is unlikely to occur from pH 7.0 to 9.0. However, pH 7.5 and 8.0 in the RAS are likely to promote greater geosmin and MIB production by S. luridiscabiei. Maintaining water pH in the RAS from 6.5 to 7.0 may decrease geosmin and MIB production by S. luridiscabiei and subsequently reduce the intensities of off-flavor problems while maintaining adequate nitrification.