Silver nanoparticle inhibition of polycyclic aromatic hydrocarbons degradation by Mycobacterium species RJGII-135.

UNLABELLED: Polycyclic aromatic hydrocarbons (PAH) are a common environmental contaminant originating from both anthropogenic and natural sources. Mycobacterium species are highly adapted to utilizing a variety of PAH. Silver nanoparticles (AgNP) are an emerging contaminant that possess bactericidal properties, interferes with the bacterial membrane and alters function. Mycobacterium sp. strain RJGII-135 provided a model bacterium to assess changes in carbon metabolism by focusing on PAH degradation, which is dependent upon passive uptake of hydrophobic molecules into the cell membrane. A mixture of 18 PAH served as a complex mixture of carbon sources for assessing carbon metabolism. At environmentally relevant PAH concentrations, RJGII-135 degraded two-, three-, and four-ring PAH within 72 h, but preferentially attacked phenanthrene and fluorene. Total cell growth and PAH degradation were successively reduced when exposed to 0·05-0·5 mg 1(-1) AgNP. However, 0·05 mg l(-1) AgNP inhibited degradation of naphthalene, acenaphthylene and acenaphthalene. RJGII-135 retained the ability to degrade the methylated naphthalenes regardless of AgNP concentration suggesting that proteins involved in dihydrodiol formation were inhibited. The reduced PAH metabolism of RJGII-135 when exposed to sublethal concentrations of AgNP provides evidence that nanoparticle pollution could alter carbon cycling in soils, sediment and aquatic environments. SIGNIFICANCE AND IMPACT OF THE STUDY: Silver nanoparticle (AgNP) pollution threatens bacterial-mediated processes due to their antibacterial properties. With the widespread commercial use of AgNP, continued environmental release is inevitable and we are just beginning to understand the potential environmental ramifications of nanoparticle pollution. This study examined AgNP inhibition of carbon metabolism through the polycyclic aromatic hydrocarbon degradation by Mycobacterium species RJGII-135. Sublethal doses altered PAH metabolism, which is dependent upon cell membrane properties and intracellular proteins. The changed carbon metabolism when exposed to sublethal doses of AgNP suggests broad impacts of this pollution on bacterial carbon cycling in diverse environments.

Reliability of mCP method for identification of Clostridium perfringens from faecal polluted aquatic environments.

AIMS: The purpose of the work was to evaluate the mCP method to correctly identify and enumerate Clostridium perfringens that are present in surface waters impacted by a mixture of faecal pollution sources. METHODS: Clostridium perfringens were enumerated and isolated from sewage influent, surface water and suspended sediments using the mCP method. Molecular characterization of isolates was performed using species-specific PCR, along with full-length sequencing of the 16S rRNA gene for a subset of isolates. RESULTS: The environmental isolates were presumptively identified as C. perfringens based on utilization of sucrose, inability to ferment cellobiose and a positive action for acid phosphatase activity. All isolates (n = 126) were classified as C. perfringens based on positive results with species-specific PCR with a subset confirmed as C. perfringens based on the 16S rRNA gene identity. CONCLUSIONS: The molecular results indicated all of the presumptive positive isolates were C. perfringens regardless of the source, e.g. sewage influent or environmental water samples. Sequencing revealed that C. perfringens obtained from sewage and the aquatic environment were nearly identical (c. 99.5% similarity). SIGNIFICANCE AND IMPACT OF THE STUDY: From this study we conclude that the mCP method is a robust approach to enumerate and isolate C. perfringens from aquatic environments that receive diverse sources of faecal pollution.

Diversity and population structure of sewage-derived microorganisms in wastewater treatment plant influent.

The release of untreated sewage introduces non-indigenous microbial populations of uncertain composition into surface waters. We used massively parallel 454 pyrosequencing of hypervariable regions in rRNA genes to profile microbial communities from eight untreated sewage influent samples of two wastewater treatment plants (WWTPs) in metropolitan Milwaukee. The sewage profiles included a discernible human faecal signature made up of several taxonomic groups including multiple Bifidobacteriaceae, Coriobacteriaceae, Bacteroidaceae, Lachnospiraceae and Ruminococcaceae genera. The faecal signature made up a small fraction of the taxa present in sewage but the relative abundance of these sequence tags mirrored the population structures of human faecal samples. These genera were much more prevalent in the sewage influent than standard indicators species. High-abundance sequences from taxonomic groups within the Beta- and Gammaproteobacteria dominated the sewage samples but occurred at very low levels in faecal and surface water samples, suggesting that these organisms proliferate within the sewer system. Samples from Jones Island (JI--servicing residential plus a combined sewer system) and South Shore (SS--servicing a residential area) WWTPs had very consistent community profiles, with greater similarity between WWTPs on a given collection day than the same plant collected on different days. Rainfall increased influent flows at SS and JI WWTPs, and this corresponded to greater diversity in the community at both plants. Overall, the sewer system appears to be a defined environment with both infiltration of rainwater and stormwater inputs modulating community composition. Microbial sewage communities represent a combination of inputs from human faecal microbes and enrichment of specific microbes from the environment to form a unique population structure.