Propidium monoazide can limit the analysis of microbial communities derived from genetic fingerprints to viable cells with intact cell membranes. However, PMA treatment cannot completely suppress polymerase chain reaction (PCR) amplification when the targeted gene is too short. PMA treatment in combination with two-step nested PCR was designed to overcome this problem. Four experiments were performed to determine the limitation of PMA treatment and to evaluate the suitability of the method by applying the following samples: (1) pure cultures of Escherichia coli O157:H7, Enterobacter aerogenes, and Alcaligenes faecalis; (2) pond water samples spiked with heat-killed E. coli O157:H7 and E. aerogenes; (3) anaerobic sludge samples exposed to increasing heat stress; and (4) selected natural samples of estuarine sediment and lake mud. Results from the first two experiments show that PMA treatment cannot efficiently suppress dead cells from PCR amplification when the targeted gene is as short as 190 bp, however, the two-step nested PCR can overcome this problem. The last two experiments indicate the method that PMA treatment in combination with two-step nested PCR is useful for viable cells detection in microbial ecology.
The biological control of cyanobacterial harmful algal blooms (cyanoHABs) is important to promote human health, environmental protection, and economic growth. Active algicidal compounds and algicidal mechanisms should be identified and investigated to control cyanoHABs. In this study, the algicidal actinobacterium Streptomyces sp. L74 was isolated from the soil of a nearby pond which located in the center lake of Guanghzou Higher Education Mega Center. Results showed that the algicidal activities of cyanoHABs are mainly achieved via an indirect attack by producing algicidal compounds. All active algicidal compounds are hydrophilic substances that are heat and pH stable. In the present study, an active compound (B3) was isolated and purified by high-performance liquid chromatography and identified as a type of triterpenoid saponin (2-hydroxy-12-oleanene-3, 28-O-D-glucopyranosyl) with a molecular formula of C42H70O13 as determined by infrared spectrometry, electrospray ionization mass spectrometry, and nuclear magnetic resonance. Active algicidal compounds from Streptomyces sp. L74 were shown to disrupt the antioxidant systems of Microcystis aeruginosa cells.
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