Engineering a Novel Metabolic Pathway for Improving Cellular Malonyl-CoA Levels in Escherichia coli

Cellular pool of malonyl-CoA in Escherichia coli is small, which impedes its utility for overproduction of natural products such as phenylpropanoids, polyketides, and flavonoids. In this study, we report the use of a new metabolic pathway to increase the malonyl-CoA concentration as a limiting metabolite in E. coli. For this purpose, the malonate/sodium symporter from Malonomonas rubra, and malonyl-CoA synthetase (MCS) from Bradyrhizobium japonicum were co-expressed in E. coli. This new pathway allows the cell to actively import malonate from the culture medium and to convert malonate and CoA to malonyl-CoA via an ATP-dependent ligation reaction. HPLC analysis confirmed elevated levels of malonyl-CoA and (2S)-naringenin as a malonyl-CoA-dependent metabolite, in E. coli. A 6.8-fold and more than 3.5-fold increase in (2S)-naringenin production were achieved in the engineered host in comparison with non-engineered E. coli and previously reported passive transport MatBMatC pathway, respectively. This observation suggests that using active transporters of malonate not only improves malonyl-CoA-dependent production but also makes it possible to harness low concentrations of malonate in culture media.

Isolation and identification of culturable halophilic bacteria with producing hydrolytic enzyme from Incheh Broun hypersaline wetland in Iran

Incheh Broun hypersaline wetland is located near the border of Turkmenistan in thenorth of Iran. This wetland is notable because of salinity (280g/l) and alteration in pH range (2.8 to 6.8). Eastern part of wetland is affected by wastewater of iodine extraction factory.  Samples were taken from soil, water and salt. Totally, 400 bacterial strains were isolated of which 194 strains were Gram-positive bacilli, 184 strains were Gram-negative rod and 22 strains were Gram-positive cocci. According to phylogenetic analysis of 16S rRNA, selected strains were placed in three taxonomic phyla including Firmicutes, Actinobacteria and Gammaproteobacteria. Optimum growth was evaluated for salt and 22 strains were found to be moderate halophile and 33 strains were halotolerant. Production of lipase, amylase, gelatinase and protease was examined. Gram-positive bacilli were the main producers of hydrolytic enzymes. Gelatinase and protease were the most frequent enzymes. Gram-positive cocci were the main producers of lipase but they didn't produce amylase.

Salinithrix halophila gen. nov., sp. nov., a halophilic bacterium in the family Thermoactinomycetaceae

A halophilic actinomycete, strain R4S8T, was isolated from soil of Inche-Broun hypersaline wetland in the north of Iran. The isolate grew aerobically at temperatures of 30–50 °C (optimum 40 °C), pH 6–10 (optimum pH 7.0) and in the presence of 1–15 % (w/v) NaCl (optimum 3–5 %). It formed short and straight to moderately flexuous aerial mycelium without motile elements. The cell wall of strain R4S8T contained meso-diaminopimelic acid as the diamino acid without any diagnostic sugars. The polar lipid pattern consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylserine, phosphatidylmonomethylethanolamine two unknown phospholipids and one unknown aminophospholipid. It synthesized anteiso-C15 : 0 (44.8 %), iso-C15 : 0 (28.8 %) and iso-C14 : 0 (8.5 %) as major fatty acids. MK-6 was the predominant respiratory quinone. The G+C content of the genomic DNA was 52.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain R4S8T belongs to the family Thermoactinomycetaceae and showed the closest 16S rRNA gene sequence similarity with Desmospora activa IMMIB L-1269T (95.5 %) and Marininema mesophilum SCSIO 10219T (95.3 %). On the basis of phylogenetic analysis and phenotypic characteristics, strain R4S8T represents a novel species in a new genus within the family Thermoactinomycetaceae , for which the name Salinithrix halophila gen. nov., sp. nov. is proposed. The type strain of the type species is R4S8T ( = IBRC-M 10813T = CECT 8506T).