001-Anthony L. Andrady. Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA. Microplastics in the marine environment. Marine Pollution Bulletin, 2011, 62 (8), 1596 - 1605.

This review discusses the mechanisms of generation and potential impacts of microplastics in the ocean environment. Weathering degradation of plastics on the beaches results in their surface embrittlement and microcracking, yielding microparticles that are carried into water by wind or wave action. Unlike inorganic fines present in sea water, microplastics concentrate persistent organic pollutants (POPs) by partition. The relevant distribution coefficients for common POPs are several orders of magnitude in favour of the plastic medium. Consequently, the microparticles laden with high levels of POPs can be ingested by marine biota. Bioavailability and the efficiency of transfer of the ingested POPs across trophic levels are not known and the potential damage posed by these to the marine ecosystem has yet to be quantified and modelled. Given the increasing levels of plastic pollution of the oceans it is important to better understand the impact of microplastics in the ocean food web.

 

Keywords: Microplastics, Nanoplastics, POPs, Plastics, Food web.

 

 

 

 

 

002-Alberto Hernandez-Eligio, Mildred Castellanos, Soledad Moreno and Guadalupe Espín. Transcriptional activation of the Azotobacter vinelandii polyhydroxybutyrate biosynthetic genes phbBAC by PhbR and RpoS. Microbiology, 2011, 157 (11), 3014 - 3023.

 

We previously showed that in Azotobacter vinelandii, accumulation of polyhydroxybutyrate (PHB) occurs mainly during the stationary phase, and that a mutation in phbR, encoding a transcriptional regulator of the AraC family, reduces PHB accumulation. In this study, we characterized the roles of PhbR and RpoS, a central regulator during stationary phase in bacteria, in the regulation of expression of the PHB biosynthetic operon phbBAC and phbR. We showed that inactivation of rpoS reduced PHB accumulation, similar to the phbR mutation, and inactivation of both rpoS and phbR resulted in an inability to produce PHB. We carried out expression studies with the wild-type, and the rpoS, phbR and double rpoS-phbR mutant strains, using quantitative RT-PCR, as well as phbB::gusA and phbR::gusA gene fusions. These studies showed that both PhbR and RpoS act as activators of phbB and phbR, and revealed a role for PhbR as an autoactivator. We also demonstrated that PhbR binds specifically to two almost identical 18 bp sites, TGTCACCAA-N4-CACTA and TGTCACCAA-N4-CAGTA, present in the phbB promoter region. The activation of phbB and phbR transcription by RpoS reported here is in agreement with the observation that accumulation of PHB in A. vinelandii occurs mainly during the stationary phase.

 

Keywords: Azotobacter vinelandii, polyhydroxybutyrate, polyhydroxybutyrate biosynthetic genes.