DNA content of free living rhizobia and bacteroids of various Rhizobium-legume associations

The DNA content of bacteroids from 22 different Rhizobium-legume associations was compared to that of the corresponding free living Rhizobium species using laser flow microfluorometry. In all 18 effective associations, the bacteroids had either similar or higher DNA content than the free living rhizobia. Bacteroid populations isolated from effective clover (Trifolium repens) and alfalfa (Medicago sativa) nodules had an average DNA content of >1.5-fold higher than free living R. trifolii and R. meliloti. These populations also contained a significant number of bacteroids with more than 3-fold the DNA content of the free living rhizobia. Populations isolated from effective nodules of winged beans (Psophocarpus tetragonolobus), peas (Pisum sativum), and mung beans (Phaseolus aureus) had an average DNA content of 1.1- to 1.5-fold higher than free living R. “cowpeas” and R. leguminosarum. Bacteroids from nodules of lupins (Lupinus angustifolius and L. minaretta), kidney beans (Phaseolus vulgaris), and soybeans (Glycine max), however, had similar DNA content to the free living forms. Two of the four associations which formed ineffective nodules contained bacteroids with lower DNA content than the free living rhizobia. The other two associations contained bacteroids with slightly higher or similar DNA content to the free living rhizobia. Nodules of the ineffective associations also did not contain leghemoglobin.     

Flow-microfluorometric analysis of Escherichia coli, Rhizobium meliloti, and Rhizobium japonicum at different stages of the growth cycle.

The applicability of flow-microfluorometry (FMF) to the study of bacterial samples was investigated on cultures of Rhizobium meliloti, Rhizobium japonicum, and Escherichia coli using fluorescent and light-scattering signals. This technique which analyzes individual bacterial cells in a population was used to monitor the relative change in nucleic acid content and cell size during the growth cycle of the three microorganisms which were known to have different growth rates. Early log-phase E. coli cells contained at least eightfold more nucleic acid and were significantly larger than the stationary-phase cells. Cultures of early log-phase R. meliloti cells contained three to four-fold more nucleic acid and were slightly larger than cells in the stationary phase. Rhizobium japonicum had very little change in either parameter. In general, the amount of change in both cell size and nucleic acid content upon initiation of log-phase growth was related to the overall growt rate of the organisms, with E. coli experiencing the greatest change and R. japonicum the least. Results obtained by FMF analysis, therefore, were consistent with observations reported by earlier workers. Cultures of R. meliloti also were used to demonstrate that the intensity of the fluorescent signals was sensitive to digestion by DNase and RNase and to prolonged storage and fixation. The potential use of FMF in the study of microorganisms is discussed.     

Separation of algal mixtures and bacterial mixtures with flow-microfluorometer using chlorophyll and ethidium bromide fluorescence

The applicability of flow-microfluorometer to separate microbial cells was demonstrated with algal and bacterial cells. Algal mixtures were sorted according to the natural chlorophyll fluorescence and the bacterial mixtures were sorted according to the fluorescence of ethidium bromide-stained nucleic acid.Abbreviation FMF Flow-microfluorometer     

The use of different eye regions in the mantis shrimp Hemisquilla californiensis Stephenson, 1967 (Crustacea: Stomatopoda) for detecting objects

A behavioral assay was used to assess the ability of the stomatopod Hemisquilla californiensis to perceive and respond to a moving target under different wavelengths and intensities of light illumination. Subjects responded to targets rotating horizontally across their visual field by a brief startle response of their eyes or antennules but did not track the targets. Under white light responses were elicited down to a light intensity of 0.9 μW cm^− 2. Responses were seen in blue light at intensities as low as 0.5 μW cm^− 2, and in green light down to 1.0 μW cm^− 2. The animals were less sensitive to red light, with no responses seen at intensities below 3.0 μW cm^− 2. Subjects did not respond to the targets at all under infrared light. This response pattern mirrors the computed sensitivity spectrum of ommatidia in the species' peripheral hemispheres but not that in most of the central bands. We conclude that this species uses the monochromatic vision in the peripheral hemispheres of its eyes to recognize objects and that the sharply tuned color receptors of the central band serve to add supplemental information if light conditions allow.