Prevalence of a novel division-level bacterial lineage in Lake Dhanmondi, Dhaka, Bangladesh, as revealed by deep sequencing of 16S rRNA gene amplicons.

A culture-independent study of the bacterial diversity in Lake Dhanmondi, located in the central region of Dhaka city, Bangladesh, was carried out using deep sequence analysis of 16S rRNA gene PCR amplicons. The results revealed the presence of a group of bacteria, termed LD11, phylogenetically unrelated to any previously cultivated bacteria at the phylum level. LD11 sequences comprised about 1.7 % of the total sequence reads after quality assessment. LD11 appears to constitute a novel division with a deep evolutionary lineage apparently branching between the Chloroflexi and Thermi-Deinococci phyla. Sequence similarity with molecular data from freshwater environments indicates that LD11 represents a widespread and novel clade of freshwater bacteria for which no cultivated representatives are yet available.

Identification of cofactor discrimination sites in NAD-isocitrate dehydrogenase from Pyrococcus furiosus.

The role of Asp-328 and Ile-329 as a cofactor discrimination site of the NAD-dependent isocitrate dehydrognase (NAD-IDH) from Pyrococcus furiosus has been verified by replacing these residues with Lys and Tyr, respectively, which are the corresponding residues in NADP-IDH from Escherichia coli. The Asp-328-Lys mutant showed dual coenzyme specificity, whereas introduction of the double mutation, Asp-328-Lys/Ile-329-Tyr shifted the cofactor preference from NAD to NADP. NADP-dependent P. furiosus IDH retained thermostability and thermoactivity compared with NAD-IDH.