A general procedure for the isolation of functionally intact phycobilisomes was devised, based on modifications of previously used procedures. It Phycobilisomes contain the phycobiliproteins which are major light-harvesting pigments in red and blue green algae (4). Isolation of PBS3 facilitates studies on characterization of their morphology, phycobiliprotein composition, and the interaction and reaggregation properties of the phycobiliproteins. PBS were first isolated without prefixation from the red alga Porphyridium cruentum in 0.5 M phosphate buffer on a sucrose step gradient at 4 C (6). The procedure was subsequently modified for some blue-green algae (1 1), but it was not generally applicable to other species, as judged from shorter wavelength fluorescence emission at 660 to 665 nm instead of 670 to 675 nm. Further modifications have been made and it was found that the most crucial condition to maintain PBS integrity, in addition to high ionic strength, is temperature. We have found that it is important that isolations be done at about 20 to 23 C, and that the phosphate buffer content be at 0.75 M (pH 6.8). The simplified procedure described here gives high PBS yields from red and blue-green algae thus far tried. These PBS exhibit the best energetic coupling of any obtainable, and are '

The microbial quality of lettuce (Lactuca sativa L. var. “Ostinata”) cultivated in a hydroponic system was evaluated. Over a 3-month study period, samples of lettuce, nutrient solution, and peat-vermiculite growing mixture from the greenhouse were analyzed for total aerobic bacteria, yeasts, molds, and coliforms. There was a consistent amount of each type of organism occurring within each sample group for a given month, and the numbers of aerobic bacteria and coliforms present were generally similar to those reported for lettuce and leafy vegetable crops propagated by the conventional method of agriculture. Over the study period, the modal values for each type of organism in lettuce were: aerobic bacteria, 7.9 × 106 CFU/g (range of 3.8 × 104 to 2.3 × 108); coliforms, 1.5 × 104 CFU/g (range of none detected to greater than or equal to 5.3 × 107); molds, 2.9 × 103 CFU/g (range of 1.2 × 102 to 5.3 × 104); and yeasts, 2.4 × 104 CFU/g (range of 6.9 × 102 to 2.3 × 106). The primary organisms associated with the growing system were Citrobacter freundii, Enterobacter cloacae, and Enterobacter agglomerans. No organisms of human health concern (i.e. Salmonella spp., Clostrium botulinum, Escherichia coli, or Staphylococcus aureus) were detected in the samples. The bacteriology of lettuce produced for market by this type of hydroponic farming and packaging appears to be generally comparable to that of field-grown lettuce and to present no unique microbiological hazards to consumers.

The authors examine the effects of undergraduate research experiences on key steps in the path to medical school, considering the case of an undergraduate research experience (URE) offered to first-year students that also might influence performance in large introductory science courses. Using a historical dataset of 15,000 first-year students, logistic and linear regressions were performed to better understand the influence of early UREs on different measures of college success. Immediate effects of an early URE on second-year course performance and very large effects on second-year retention are demonstrated. There also are delayed effects on taking the MCAT and medical school acceptance. Results demonstrate the importance of early UREs and their role in STEM student persistence.

Salmonella typhimurium (ATCC 14028) was inoculated into nutrient solution collected from a hydroponic lettuce farm. The objective was to determine the effect of the presence or absence of the normal microflora of the nutrient solution on growth and persistence of Salmonella. In the unsterilized nutrient solution, Salmonella did not exceed 104 CFU ml−1, even when introduced at that concentration in the presence of a starting total aerobic count of 103 CFU ml−1 for the normal flora. Growth of Salmonella appeared to be suppressed, while that of the normal flora was unaffected and reached the usual level of 105 – 106 CFU ml−1 by 24 h. The normal microflora apparently restricted growth of Salmonella, and by 48 h after its introduction, Salmonella counts were decreasing. Salmonella inoculated into filter-sterilized nutrient solution grew rapidly to as high as 108 CFU ml−1, demonstrating that the nutrient solution contained the elements necessary to promote exponential growth of the bacterium. However, the fact that these levels were not achieved in the presence of other organisms, strongly suggests that Salmonella could not compete favorably with the normal flora of the hydroponic system.