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  • Thumbnail for The barrier that prevents penicillin catabolism genes from transferring from ABC 07 to ADP1
    The barrier that prevents penicillin catabolism genes from transferring from ABC 07 to ADP1 by Bao, Yiqiao

    There are hundreds of phylogenetically diverse soil bacteria with the capacity to grow on a wide range of antibiotics as their sole carbon source. Some of these bacteria are closely related to human pathogens. The present study evaluates whether there is a barrier that might prevent the penicillin catabolism genes from transferring from the penicillin catabolism strain ABC 07 to the Acinetobacter baylyi strain ADP1. Because of its natural competence and its close relation to the human pathogen Acinetobacter baumanni, ADP1 is an ideal model for the current investigation. ADP1 was transformed with the genomic DNA of ABC 07, Sau3A1 genomic libraries, and Sau3A1 genomic plasmid libraries to test this barrier. None of these methods transformed ADP1 to be a strain with a penicillin catabolism phenotype. In this regard, recent research (Walsh et al., 2013) challenges the concept of bacteria subsisting on antibiotics and argues that the SCS selective medium used in the original study (Dantas et al, 2008) contains 15 mg/L EDTA, which could be the carbon source that sustained the growth of these “antibiotic-eaters.” The present study also tested and verified that ABC 07 can subsist on penicillin, but not EDTA. These results suggest that antibiotic catabolism genes cannot be readily transferred from antibiotic catabolism strains to other bacteria. Future research related to antibiotic catabolism phenotype should attempt computational approaches and system-level molecular methods to identify antibiotic catabolism genes and metabolic pathways before further characterizing their clinical and ecological implications.

  • Thumbnail for Repeating earthquakes in the Darfield region, New Zealand
    Repeating earthquakes in the Darfield region, New Zealand by Armstrong, Ryan Scott

    The M 7.1 3 September 2010 Darfield, New Zealand, earthquake ruptured a previously unknown fault system. Fault-slip models (e.g., Beavan et al., 2010; Holden et al., 2011; Eliott et al., 2012) have been calculated using InSAR, GPS, and seismic data. They show that although the rupture initiated on a SW-dipping thrust fault, the majority of fault motion was right-lateral strike slip from the surface to 10 km depth. The InSAR data used in the geodetic model provide the cumulative ground motion due to the Darfield earthquake and some early aftershocks, while the seismic model utilizes waveforms for the mainshock, limiting the solution to slip during the initial rupture. This study utilizes cross correlation methods to identify repeating earthquakes within continuous seismic waveforms from the Canterbury region, New Zealand between September 2010 and January 2011. Repeating events indicate portions of fault segments that are not locked, possibly due to high pore pressure (Bisrat et al. 2012), and thus can indirectly identify locked areas of fault segments. Despite the fact that our method initially recognized 8 groups of potentially repeating earthquakes, a cross correlation check at a second station indicates that none of the identified earthquakes are truly repeating earthquakes. Our method provides negative results, which indicate repeating earthquakes may not be present within the Darfield fault complex, although it remains unclear whether they are truly absent or the methodology is not sufficient to detect them. While our method failed to identify repeating earthquakes, it possibly identified clusters of events with similar focal mechanisms In theory, our study shows a direct relationship between the compactness of a cluster and the similarity of focal mechanisms.