Accumulation of toxic concentrations of methylglyoxal by wild-type Escherichia coli K-12

Wild-type strains of Escherichia coli K-12 accumulate toxic concentrations of methylglyoxal when grown in medium containing adenosine 3',5'-monophosphate and either d-xylose, l-arabinose, or d-glucose-6-phosphate, independent of the presence of other carbon sources. Mutations at a locus called cxm specifically block methylglyoxal formation from xylose in the presence of adenosine 3',5'-monophosphate. Accumulation in medium containing xylose, studied in some detail, is dependent on the ability to utilize xylose and is associated with an increased rate of xylose utilization without changes in levels of xylose isomerase. These results suggest that adenosine 3',5'-monophosphate results in induction of excessively high levels of an early rate-limiting step in xylose metabolism. This step may be the transport of xylose into the cell. The resulting excessive rates of xylose catabolism could stimulate methylglyoxal formation by overburdening late steps in glycolysis.     

Augmentation of the effect of doxorubicin with low-dose tumor necrosis factor in experimental liver metastasis

The antitumor activity of recombinant human tumor necrosis factor was studied in vivo as a single agent and in combination with a conventional chemotherapeutic agent. Dosages of tumor necrosis factor of 100 micrograms, 50 micrograms, and 25 micrograms were injected intraportally in Sprague-Dawley rats containing hepatic implants of Walker carcinosarcoma. An effect on the tumor was seen but was associated with a significant acute mortality. Lower dosages of tumor necrosis factor, 10 micrograms, 5 micrograms, and 1 microgram, administered with 10 mg/kg of doxorubicin (Adriamycin) significantly enhanced the antitumor effect of doxorubicin without an acute mortality. This suggests that lower dosages of tumor necrosis factor with conventional chemotherapy may augment the latter's effect without any added toxicity.     

Riverine transport and nutrient inputs affect phytoplankton communities in a coastal embayment

1. Rivers often transport phytoplankton to coastal embayments and introduce nutrients that can enrich coastal plankton communities. We investigated the effects of the Nottawasaga River on the nearshore (i.e. within 500 μm of shore) phytoplankton composition along a 10-km transect of Nottawasaga Bay, Lake Huron in 2015 and 2016. Imaging flow cytometry was used to identify and enumerate algal taxa, which were resolved at sizes larger than small nanoplankton (i.e. >5 μm). Multivariate analysis (perMANOVA and redundancy analysis) and a dilution model were used to examine how nutrients and the transport of algal taxa affected community composition in the bay.
2. Sampling stations with different percentages of river water had significantly different phytoplankton communities. Phytoplankton community composition was also strongly associated with nutrients, including total phosphorus, which also varied with the percentage of river water. The majority of the 51 phytoplankton taxa identified in 2016 had numerical abundances in the bay that could be explained simply by the dilution of incoming river water.
3. Phytoplankton transported from the river had a higher proportion of edible-sized cells (<30 μm), particularly in summer when colonial cyanobacteria were numerically dominant in the bay. Six taxa were more abundant than expected from the dilution of river water and included some cyanobacteria with late summer maxima. Five of the taxa that were transported from the river were less abundant than expected in the bay.
4. Whereas impacts of fertilisation due to the characteristically higher nutrient concentration in the river are to be expected, the strong and highly correlated effects of transport within the narrow coastal band of this study largely concealed any distinct fertilisation effects.
5. Riverine inputs may strongly influence the nearshore assemblage of phytoplankton in oligotrophic embayments in large lakes, creating hotspots for productivity, species turnover, and trophic dynamics.