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Platform chemicals such as medium-chain carboxylic acids (MCCAs) can be produced from organic waste streams via chain elongation in anaerobic mixed-culture bioreactors. A product recovery system is needed to collect MCCAs from the bioreactor effluent. Membrane-based liquid-liquid extraction, the most commonly used product recovery approach, requires suspended solids removal from the bioreactor effluent to avoid membrane fouling. An anaerobic dynamic membrane bioreactor (AnDMBR) was developed to evaluate MCCA production from brewery and prefermented food waste and to produce a permeate with low suspended solids to facilitate downstream product recovery. The AnDMBR employed an inexpensive stainless-steel mesh as the support material for the development of a biofilm or dynamic membrane, which was responsible for solids-liquid separation. The AnDMBR produced a permeate quality with an average total suspended solids (TSS) concentration of 0.12 g L-1, while the average bioreactor TSS concentration was two orders of magnitude higher (21.6 g L-1). A maximum solids removal efficiency of ≥99% was achieved and good permeate quality was sustained for over 200 days without fouling control or cleaning the support material. In addition to solids-liquid separation, the dynamic membrane was responsible for a substantial fraction of the biological activity of the AnDMBR. The relative activity of Clostridiales, as determined by 16S rRNA sequencing, correlated with MCCA production and was higher in the dynamic membrane (20.0 ± 4.9%) than in the suspended biomass (5.2 ± 2.7%) in the bioreactor. This observation was consistent with MCCA production data as the permeate MCCA concentrations were significantly (p = 8.2 × 10-5) higher than that in the bioreactor, suggesting that the dynamic membrane biofilm contributed to chain elongation.

Smets, Ilse, Adrian Caplanusi, Sanda Despa, Zsolt Molnar, Mihai Radu, Martin vandeVen, Marcel Ameloot, and Paul Steels. [Ca.sup.2+] uptake in mitochondria occurs via the reverse action of the [Na.sup.+]/[Ca.sup.2+] exchanger in metabolically inhibited MDCK cells. Am J Physiol Renal Physiol 286: F784-F794, 2004. First published December 9, 2003; 10.1152/ajprenal.00284.2003.--In ischemic or hypoxic tissues, elevated [Ca.sup.2+] levels have emerged as one of the main damaging agents among other [Ca.sup.2+]-independent mechanisms of cellular injury. Because mitochondria, besides the endoplasmic reticulum, play a key role in the maintainance of cellular [Ca.sup.2+] homeostasis, alterations in the mitochondrial [Ca.sup.2+] content ([[Ca.sup.2+].sub.m]) were monitored in addition to changes in cytosolic [Ca.sup.2+] concentration ([[Ca.sup.2+].sub.i]) during metabolic inhibition (MI) in renal epithelial Madin-Darby canine kidney (MDCK) cells. [[Ca.sup.2+].sub.i] and [[Ca.sup.2+].sub.m] were monitored via, respectively, fura 2 and rhod 2 measurements. MI induced an increase in [[Ca.sup.2+].sub.i] reaching 631 [+ or -] 78 nM in ~20 min, followed by a decrease to 118 [+ or -] 9 nM in the next ~25 min. A pronounced drop in cellular ATP levels and a rapid increase in intracellular [Na.sup.+] concentrations in the first 20 min of MI excluded [Ca.sup.2+] efflux in the second phase via plasma membrane ATPases or [Na.sup.+]/[Ca.sup.2+] exchangers (NCE). Mitochondrial rhod 2 intensities increased to 434 [+ or -] 46% of the control value during MI, indicating that mitochondria sequester [Ca.sup.2+] during MI. The mitochondrial potential ([DELTA][[PSI].sub.m]) was lost in 20 min of MI, excluding mitochondrial [Ca.sup.2+] uptake via the [DELTA][[PSI].sub.m]-dependent mitochondrial [Ca.sup.2+] uniporter after 20 min of MI. Under [Na.sup.+]-free conditions, or when CGP-37157, a specific inhibitor of the mitochondrial NCE, was used, no drop in [[Ca.sup.2+].sub.i] was seen during MI, whereas the MI-induced increase in mitochondrial rhod 2 fluorescence was strongly reduced. To our knowledge, this study is the first to report that in metabolically inhibited renal epithelial cells mitochondria take up [Ca.sup.2+] via the NCE acting in the reverse mode. renal epithelial cells; intramitochondrial calcium; rhod 2; CGP-37157

In renal ischemia, tubular obstruction induced by swelling of epithelial cells might be an important mechanism for reduction of the glomerular filtration rate. We investigated ischemic cell swelling by examining volume regulation of A6 cells during metabolic inhibition (MI) induced by cyanide and 2-deoxyglucose. Changes in cell volume were monitored by recording cell thickness ([T.sub.c]). Intracellular pH (p[H.sub.c]) measurements were performed with the pH-sensitive probe 5-chloromethyl-fluoresceine diacetate. [T.sub.c] measurements showed that MI increases cell volume. Cell swelling during MI is proportional to the rate of [Na.sup.+] transport and is not followed by a volume regulatory response. Furthermore, MI prevents the regulatory volume decrease (RVD) elicited by a hyposmotic shock. MI induces a pronounced intracellular acidification that is conserved during a subsequent hypotonic shock. A transient acidification induced by a N[H.sub.4]Cl prepulse causes a marked delay of the RVD in response to a hypotonic shock. On the other hand, acute lowering of external pH to 5, simultaneously with the hypotonic shock, allowed the onset of RVD. However, this RVD was completely arrested ~10 min after the initiation of the hyposmotic challenge. The inhibition of RVD appears to be related to the pronounced acidification that occurred within this time period. In contrast, when external pH was lowered 20 min before the hyposmotic shock, RVD was absent. These data suggest that internal acidification inhibits cellular volume regulation in A6 cells. Therefore, the intracellular acidification associated with MI might at least partly account for the failure of volume regulation in swollen epithelial cells. distal tubular epithelial cell line; chemical ischemia; cyanide; 2-deoxyglucose; pH-sensitive fluorescent probe 5-chloromethylfluoresceine diacetate; hyposmotic shock; regulatory volume decrease

Researchers have developed a model to measure the influence of oxygen on gene expression. This model can be used to measure the influence of any external signal on gene expression. Gene expression is commonly measured by fusing a reporter gene to the gene under observation.