Genome analysis of Geitlerinema sp. CT7802, a highly halotolerant, thermotolerant Geitlerinema sp. from the Gulf of Arabia

Geitlerinema sp. CT7802 is a highly halotolerant, thermotolerant marine cyanobacterium that was isolated from an industrial brine outfall site in the Eastern Province of Saudi Arabia. To investigate the genetic and metabolic potential of this organism, a complete genome sequence was determined using Illumina 105 bp paired end reactions and assembled using IDBA A5 pipeline. The scaffold genome (368 contigs) has been generated. The CT7802 genome assembly was annotated using FGENESB pipeline. The genome is 6.31 Mb with a 58.5% G+C content, and encodes 5162 protein genes, 58 RNA genes and 2772 promoter genes. Genome predictions identified a 14.2 kb nitrogenase gene cluster encoding nifBSUHDKZEXW indicated this strain was capable of nitrogen fixation. To investigate this, Geitlerinema CT7802 was cultured in the presence and absence of nitrogen sources and cell growth measured quantitatively. This confirmed an active nitrogenase in CT7802. Additional investigations of the genomic basis for halotolerance and thermotolerance were carried out using a global transcriptome profile of Synechococcus sp. strain PCC 7002. For this analysis, we have used reciprocal blast to map the CT7802 genes to those of Synechococcus sp. strain PCC 7002. We have identified a total of 2124 orthologous CDSs. The recent web publication of a genome sequence for the stenohaline Geitlerinema sp. PCC7407 allowed comparative analysis with CT7802 genome. This reveals a shared genomic content of 2460 genes with 2702 and 1355 genes unique to CT7802 and PCC7407 respectively. These observations indicate that considerable genomic heterogeneity exists between these two strains.