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Taking advantage of asymmetric ion transport in nanopipettes, the surface charges of various substrates have been successfully imaged by scanning ion conductance microscopy (SICM). The predominant electrostatic interaction between charged nanopipettes and substrates thus needs to be better elucidated and quantified, as traditional SICM theory is not adequate to describe the resulting ion current. Herein, we use both experimental and simulation methods to study the asymmetric ion‐transport processes in nanopipettes near charged substrates, and correlate surface charge and geometry parameters to the resulting ionic current. It is found that for negatively charged substrates and nanopipettes, positive feedback responses are displayed at the high conductivity states, and they are sensitive to the applied voltages and surface charges. While at the low conductivity states, comparable negative feedback responses are largely independent of experimental conditions. The elucidated and quantified asymmetric ion transport features would allow more accurate measurements and analysis for approaching and surface charge mapping in SICM applications. [ABSTRACT FROM AUTHOR]

Cyanophages are abundant in the oceanic environment and directly impact cyanobacterial distributions, physiological processes and evolution. Two samples collected from coastal Maine in July and September 2009 were enriched for S ynechococcus cells using flow cytometry and examined through metagenomic sequencing. Homology-based sequence prediction indicated cyanophages, largely myoviruses, accounted for almost half the reads and provided insights into environmental infection events. T4-phage core-gene phylogenetic reconstruction revealed unique diversity among uncultured cyanophages and reference isolates resulting in identification of a new phylogenetic cluster. Genomic comparison of reference cyanophage strains S- SM2 and Syn1 with putative homologous contigs recovered from metagenomes provided evidence that gene insertion, deletion and recombination have occurred among, and are likely important for diversification of, natural populations. Identification of putative genetic exchange between cyanophage and non-cyanophage viruses, i.e. M icromonas virus and P elagibacter phage, supports hypotheses related to a significant role for viruses in mediating transfer of genetic material between taxonomically diverse organisms with overlapping ecological niches. [ABSTRACT FROM AUTHOR]

Summary Plasmid diversity is still poorly understood in pelagic marine environments. Metagenomic approaches have the potential to reveal the genetic diversity of microbes actually present in an environment and the contribution of mobile genetic elements such as plasmids. By searching metagenomic datasets from flow cytometry-sorted coastal California seawater samples dominated by cyanobacteria (SynMeta) and from the Global Ocean Survey (GOS) putative marine plasmid sequences were identified as well as their possible hosts in the same samples. Based on conserved plasmid replication protein sequences predicted from the SynMeta metagenomes, PCR primers were designed for amplification of one plasmid family and used to confirm that metagenomic contigs of this family were derived from plasmids. These results suggest that the majority of plasmids in SynMeta metagenomes were small and cryptic, encoding mostly their own replication proteins. In contrast, probable plasmid sequences identified in the GOS dataset showed more complexity, consistent with a much more diverse microbial population, and included genes involved in plasmid transfer, mobilization, stability and partitioning. Phylogenetic trees were constructed based on common replication protein functional domains and, even within one replication domain family, substantial diversity was found within and between different samples. However, some replication protein domain families appear to be rare in the marine environment. [ABSTRACT FROM AUTHOR]