Based on the increase of 16S rRNA gene sequences in databases it is possible\ud to design improved oligonucleotide primers for this gene. Primers were designed in\ud silico to specifically amplify fragments of the gene from the Alpha, Beta and Gamma\ud subgroups of the Proteobacteria, as well as from Bacteroidetes, Firmicutes,\ud Cyanobacteria and Planctomycetes and tested in silico and in vitro.\ud The aim was to investigate bacterioplankton diversity and reveal greater\ud fingerprint diversity within these groups than is possible using primers specific for the\ud entire domain Bacteria, and also to reduce clone library redundancy. It was then\ud aimed to investigate the potential impacts of increased pCO2 and ocean fertilisation\ud with iron (Fe) and phosphorus (P), on bacterioplankton diversity. Group-specific\ud clone libraries representing contrasting marine regions were analysed, and the\ud usefulness and specificity of the primers validated. The clone libraries showed\ud members of the oligotrophic marine group (OMG) to be present in an in situ coastal\ud mesocosm supplemented with nutrients.\ud The newly-developed group-specific primers were used in combination with\ud an improved method of denaturing gradient gel electrophoresis (DGGE) to profile in\ud detail bacterial communities in mesocosms, which were maintained at 750 ppm of\ud pCO2, the level projected for the global surface ocean in the year 3000, and 380 ppm\ud of CO2, the present level. Increased pCO2 correlated with a decrease in abundance of\ud some members of the Gammaproteobacteria. Otherwise there was little impact on\ud diversity due to raised pCO2.\ud The same DGGE protocol was applied to samples from an ocean Fe and P\ud fertilisation experiment. Diversity change due to Fe was not evident. However in\ud seawater amended with P there was an explosive growth of some cells with 16S\ud rRNA genes similar to those of the SAR86 clade, and others with similarity to\ud Gammaproteobacteria with large genomes such as Oceanospirillum sp. and\ud Psychromonas sp
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