Catenovulum adriaticum sp. nov., isolated from algae in the harbour of Susak, Croatia.

The use of algae as feedstock for industrial purposes, such as in bioethanol production, is desirable. During a search for new agarolytic marine bacteria, a novel Gram-stain-negative, strictly aerobic, and agarolytic bacterium, designated as TS8T, was isolated from algae in the harbour of the island of Susak, Croatia. The cells were rod-shaped and motile. The G+C content of the sequenced genome was 38.6 mol%. Growth was observed at 11-37 °C, with 0.5-13 % (w/v) NaCl, and at pH 6.0-9.0. The main fatty acids were summed feature 3 (C16 : 1 ω6c and/or C16 : 1 ω7c), summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c), and C16 : 0. The main respiratory quinone was ubiquinone-8. The major polar lipids were phosphatidylethanolamine and phosphatidylglycerol. Analysis of 16S rRNA gene sequences indicated that the newly isolated strain belongs to the genus Catenovulum. Based on 16S rRNA gene sequence data, strain TS8T is closely related to Catenovulum sediminis D2T (95.7 %), Catenovulum agarivorans YM01T (95.0 %), and Catenovulum maritimum Q1T (93.2 %). Digital DNA-DNA hybridization values between TS8T and the other Catenovulum strains were below 25 %. Based on genotypic, phenotypic, and phylogenetic data, strain TS8T represents a new species of the genus Catenovulum, for which the name Catenovulum adriaticum sp. nov. is proposed. The type strain is TS8T (=DSM 114830T=NCIMB 15451T).

Heterologous Production of Isopropanol Using Metabolically Engineered Acetobacterium woodii Strains.

The depletion of fossil fuel resources and the CO2 emissions coupled with petroleum-based industrial processes present a relevant issue for the whole of society. An alternative to the fossil-based production of chemicals is microbial fermentation using acetogens. Acetogenic bacteria are able to metabolize CO or CO2 (+H2) via the Wood-Ljungdahl pathway. As isopropanol is widely used in a variety of industrial branches, it is advantageous to find a fossil-independent production process. In this study, Acetobacterium woodii was employed to produce isopropanol via plasmid-based expression of the enzymes thiolase A, CoA-transferase, acetoacetate decarboxylase and secondary alcohol dehydrogenase. An examination of the enzymes originating from different organisms led to a maximum isopropanol production of 5.64 ± 1.08 mM using CO2 + H2 as the carbon and energy source. To this end, the genes thlA (encoding thiolase A) and ctfA/ctfB (encoding CoA-transferase) of Clostridium scatologenes, adc (encoding acetoacetate decarboxylase) originating from C. acetobutylicum and sadH (encoding secondary alcohol dehydrogenase) of C. beijerinckii DSM 6423 were employed. Since bottlenecks in the isopropanol production pathway are known, optimization of the strain was investigated, resulting in a 2.5-fold increase in isopropanol concentration.

Engineering Acetobacterium woodii for the production of isopropanol and acetone from carbon dioxide and hydrogen.

The capability of four genetically modified Acetobacterium woodii strains for improved production of acetone from CO2 and hydrogen was tested. The acetone biosynthesis pathway was constructed by combining genes from Clostridium acetobutylicum and Clostridium aceticum. Expression of acetone production genes was demonstrated in all strains. In bioreactors with continuous gas supply, all produced acetic acid, acetone, and, surprisingly, isopropanol. The production of isopropanol was caused by an endogenous secondary alcohol dehydrogenase (SADH) activity at low gas-feeding rate. Although high amounts of the natural end product acetic acid of A. woodii were formed,14.5 mM isopropanol and 7.6 mM acetone were also detected, showing that this is a promising approach for the production of new solvents from C1 gases. The highest acetic acid, acetone, and isopropanol production was detected in the recombinant A. woodii [pJIR750_ac1t1] strain, with final concentrations of 438 mM acetic acid, 7.6 mM acetone, and 14.5 mM isopropanol. The engineered strain A. woodii [pJIR750_ac1t1] was found to be the most promising strain for acetone production from a gas mixture of CO2 and H2 and the formation of isopropanol in A. woodii was shown for the first time.