No abstract

Long residence times of probiotics in the intestinal tract would prolong their potential beneficial health effects and assist colonization. This study investigated the colonization potential of Lactobacillus casei Shirota in mouse intestine by using 5 (and 6)-carboxyfluorescein diacetate, succinimidyl ester (cFDA-SE) for assessment of doubling times in different parts of the intestine. The amounts of intestinal water overlying the surfaces of the duodenum, jejunum, ileum, and colon in BALB/c mice were 34.4 ؎ 2.9, 58.8 ؎ 6.8, 21.6 ؎ 2.2, and 8.0 ؎ 1.0 mg, respectively. Based on the residual concentrations of cFDA-SE-labeled lactobacilli on intestinal mucosal surfaces, the average half times for the wash-out of lactobacilli fed were estimated at 3.98, 1.55, 1.34, and 2.48 days in the duodenum, jejunum, ileum, and colon, respectively. The average doubling times of the lactobacilli, estimated from the residual fluorescent levels of surface-adhered cells, were 4.10, 4.78, 4.56, and 5.59 days in the duodenum, jejunum, ileum, and colon, respectively. It is estimated that the lactobacilli would have to achieve an average doubling time of 1.03 to 2.04 days to colonize the various sections of the mouse intestinal tract more permanently.Probiotic intestinal bacteria beneficially influence the health of the host by modulating the metabolic activities, immunity, and microbiota in the host's intestine (7,12). Lactobacilli have been used as antigen and cytokine delivery vehicles for oral immunization and disease treatment (11,16). Probiotic bacteria are selected for their beneficial health properties as well as their ability to tolerate intestinal conditions and achieve high growth rates in culture (13). However, no probiotic lactobacilli used in clinical trials and commercial production have been demonstrated to persist in fecal samples for more than a few weeks after their administration has been stopped (4,5,14,15). Such an effect is termed colonization resistance. The ability of exogenously administered probiotics to adhere to the mucosal cells and multiply in the intestinal tract has been questioned (2). There are recent reports on the recovery of consumed lactobacilli from human colonic biopsies after discontinuation of probiotic administration (1, 3, 18), thus providing direct evidence that probiotic lactobacilli are able to temporary colonize colonic mucosae. Prolonged adhesion and colonization of probiotic bacteria on intestinal mucosal surfaces could favor probiotic effects. The aim of this study was to understand the growth and colonization of lactobacilli in the intestinal tract, using the mouse as the model system. MATERIALS AND METHODSPreparation of fluorogenic dye. Five (and 6)-carboxyfluorescein diacetate, succinimidyl ester (cFDA-SE), is a nonfluorescent membrane-permeative ester which nonspecific prokaryotic and eukaryotic intracellular esterases convert to a fluorescent derivative that in turn is then covalently linked to intracellular proteins via the probe's succinimidyl group (19). cFDA-SE (2 mg) (Molecul...

SummaryBioengineering of photoautotrophic microalgae into CO 2 scrubbers and producers of valueadded metabolites is an appealing approach in low-carbon economy. A strategy for microalgal bioengineering is to enhance the photosynthetic carbon assimilation through genetically modifying the photosynthetic pathways. The halotolerant microalgae Dunaliella posses an unique osmoregulatory mechanism, which accumulates intracellular glycerol in response to extracellular hyperosmotic stresses. In our study, the Calvin cycle enzyme sedoheptulose 1,7-bisphosphatase from Chlamydomonas reinhardtii (CrSBPase) was transformed into Dunaliella bardawil, and the transformant CrSBP showed improved photosynthetic performance along with increased total organic carbon content and the osmoticum glycerol production. The results demonstrate that the potential of photosynthetic microalgae as CO 2 removers could be enhanced through modifying the photosynthetic carbon reduction cycle, with glycerol as the carbon sink.

An a-shape tubular photobioreactor was designed and constructed based on knowledge of algal growth physiology using sunlight. The algal culture is lifted 5 m by air to a receiver tank. From the receiver tank, the culture flows down parallel polyvinyl-chloride tubes of 25 m length and 2.5 cm internal diameter, placed at an angle of 25 with the horizontal to reach another set of air riser tubes. Again the culture is lifted 5 m to another receiver tank, then flows down parallel tubes connected to the base of the first set of riser tubes. Thus, the bioreactor system looks like the symbol a. As there is no change in the direction of the liquid flow, high liquid flow rate and Reynolds Number can be achieved at relatively low air flow rate in the riser tubes. Due to the high area-volume ratio of the bioreactor, and equable photosynthetically available radiance and culture temperature, biomass density of exceeding 10 g dry weight L -l and daily output rate of 72 g dry weight m -2 land d-' were achieved.

The unicellular halotolerant green alga species Dunaliella are able to proliferate in extremely varied salinities by synthesizing intracellular glycerol and adjusting the cell shape and volume. However, some marine Dunaliella species such as Dunaliella tertiolecta are not able to regulate cell volume as an immediate response to counter external osmotic shock. Here we report that a rapid shock‐response mechanism is present in Dunaliella tertiolecta, involving uptake of exogenous glycerol in response to hyperosmotic shock without changing cell volume, and this glycerol uptake activity is associated with the Dunaliella tertiolecta glycerol uptake protein 1 (DtGUP1) gene, which belongs to the membrane‐bound O‐acyltransferase. The mutant DtGUP1‐E, in which the DtGUP1 gene is silenced, displayed an inability to take up glycerol from the medium and showed cell death under hyperosmotic shock. To our knowledge, this is the first time a gene product has been reported in Dunaliella tertiolecta that is involved in glycerol uptake activity under hyperosmotic stress.