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Abstract: The green sulfur bacterium Chlorobium limicola UdG6040 exhibited a significant change in the spectral properties of its antenna when transferred from batch culture to a sulfide-limited chemostat. In steady-state continuous cultures, the in vivo absorption maximum of the culture changed to shorter wavelengths according to the dilution rate. The maximum difference observed was of 15 nm when cells were growing at 0.087 h–1. HPLC analyses revealed that the observed spectral change was caused by a partial enrichment of the original BChl c-containing antenna with BChl d molecules together with a change in the homolog composition of both pigments. The relative amount of BChl d reached a maximum value of 50% when cells were growing at 0.087 h–1. The content of BChl d decreased to less than the 22% when the dilution rate was diminished to 0.015 h–1. An unbalance of pigment synthesis at high dilution rates is suspected to be responsible of the changes observed in the antenna composition. Chlorosomes isolated from Chl. limicola UdG6040 growing at 0.070 h–1 contain organised pools of BChl c and BChl d in equal amounts.

Abstract: The uptake of soluble phosphate by the green sulfur bacterium Chlorobium limicola UdG6040 was studied in batch culture and in continuous cultures operating at dilution rates of 0.042 or 0.064 h–1. At higher dilution rates, washout occurred at phosphate concentrations below 7.1 μM. This concentration was reduced to 5.1 μM when lower dilution rates were used. The saturation constant for growth on phosphate (K μ) was between 2.8 and 3.7 μM. The specific rates of phosphate uptake in continuous culture were fitted to a hyperbolic saturation model and yielded a maximum rate (Va max) of 66 nmol P (mg protein)–1 h–1 and a saturation constant for transport (K t) of 1.6 μM. In batch cultures specific rates of phosphate uptake up to 144 nmol P (mg protein)–1 h–1 were measured. This indicates a difference between the potential transport of cells and the utilization of soluble phosphate for growth, which results in a significant change in the specific phosphorus content. The phosphorus accumulated within the cells ranged from 0.4 to 1.1 μmol P (mg protein)–1 depending on the growth conditions and the availability of external phosphate. Transport rates of phosphate increased in response to sudden increases in soluble phosphate, even in exponentially growing cultures. This is interpreted as an advantage that enables Chl. limicola to thrive in changing environments.

New strategies in inoculation and operation of bioelectrochemical systems were used to advance in the steering of bio-electro carbon dioxide (CO2) recycling towards chemical compounds. First, the preparation of microbe coated biocathodes ex-situwith putative electroactive species with CO2as sole carbon source was assayed. Second, CO2feeding strategies for the operation of BES systems were explored to ensure enough reducing power during batch mode operation. The impact on the proposed changes on the product portfolio and production yields was assessed. The initial enrichment of a putative electroactive community on bare electrode surfaces was proven to be successful and led to a shortening of the start-up period of the system from days to hours. Moreover, the establishment of a new feeding procedure to favor the presence of elevated reducing power availability for cells triggered the production of longer carbon chain carboxylates (max. 0.99 gbutyratem−2electroded−1) and alcohols (max. 0.83 gethanolm−2electroded−1) at early stages of experiment. This work complements the recent knowledge on the control of bioelectrochemical processes by the establishment of strategies to obtain target added-value compounds from CO2.