Viability, strength, and fragmentation of Saccharopolyspora erythraea in submerged fermentation.

Two fermentations of the commercially important erythromycin-producing filamentous bacterium Saccharopolyspora erythraea were conducted in defined media. One was glucose-limited and the other nitrate-limited. The viability of the hyphae was determined using the fluorescent stain BacLight (Molecular Probes, Eugene, OR). Also, the force required to strain hyphae to breakage was determined using micromanipulation and a sensitive force transducer. In both fermentations, fragmentation coincided with the appearance of regions in the mycelia with permeabilised membranes (considered nonviable). Under glucose-limitation, hyphal breaking force rose to 1,050 +/- 130 nN at the end of the growth phase and fell to an undetectable value as a result of glucose exhaustion. Under nitrate-limitation, hyphal breaking force fell from 900 +/- 160 nN during the growth phase to 550 +/- 40 nN in the stationary phase. In both cases image analysis showed that the dimensions of mycelia were of the same order, suggesting that the major factor influencing fragmentation was the appearance of nonviable regions (assumed to be weak). The location in which nonviable regions first appear within hyphae could not be determined because of their appearance coinciding with fragmentation.     

FOSSIL FUNGI (ENDOGONACEAE) FROM THE TRIASSIC OF ANTARCTICA

Fungal sporocarps are described from Triassic silicified peat deposits from Antarctica. Sporocarps possess a two-layered wall and contain a single spore. The outer layer is mycelial; the inner layer, noncellular. The combination of primitive and advanced features suggests that this fungus is intermediate in complexity between the lower and evolutionarily more advanced fungi. The Antarctic fungus and morphologically similar fossils resemble extant members of the Endogonaceae, but appear to have been saprophytes rather than mycorrhizal symbionts.     

Metabolic cost of generating muscular force in human walking: insights from load-carrying and speed experiments.

We sought to understand how leg muscle function determines the metabolic cost of walking. We first indirectly assessed the metabolic cost of swinging the legs and then examined the cost of generating muscular force during the stance phase. Four men and four women walked at 0.5, 1.0, 1.5, and 2.0 m/s carrying loads equal to 0, 10, 20, and 30% body mass positioned symmetrically about the waist. The net metabolic rate increased in nearly direct proportion to the external mechanical power during moderate-speed (0.5-1.5 m/s) load carrying, suggesting that the cost of swinging the legs is relatively small. The active muscle volume required to generate force on the ground and the rate of generating this force accounted for >85% of the increase in net metabolic rate across moderate speeds and most loading conditions. Although these factors explained less of the increase in metabolic rate between 1.5 and 2.0 m/s ( approximately 50%), the cost of generating force per unit volume of active muscle [i.e., the cost coefficient (k)] was similar across all conditions [k = 0.11 +/- 0.03 (SD) J/cm3]. These data indicate that, regardless of the work muscles do, the metabolic cost of walking can be largely explained by the cost of generating muscular force during the stance phase.     

Analysis of the distribution and structure of integrated Banana streak virus DNA in a range of Musa cultivars

Banana streak virus strain OL (BSV-OL) commonly infects new Musa hybrids, and this infection is thought to arise de novo from integrated virus sequences present in the nuclear genome of the plant. Integrated DNA (Musa6+8 sequence) containing the whole genome of the virus has previously been cloned from cv. Obino l’Ewai (Musa AAB group), a parent of many of the hybrids. Using a Southern blot hybridization assay, we have examined the distribution and structure of integrated BSV-OL sequences in a range of Musa cultivars. For cv. Obino l’Ewai, almost every restriction fragment hybridizing to BSV-OL was predicted from the Musa6+8 sequence, suggesting that this is the predominant type of BSV-OL integrant in the genome. Furthermore, since only two junction fragments of Musa/BSV sequence were detected, and the Musa6+8 sequence is believed to be integrated as multiple copies in a tandem array, then the internal Musa spacer sequences must be highly conserved. Similarly sized restriction fragments were detected in four BB group cultivars, but not in six AA or AAA group cultivars, suggesting that the BSV-OL sequences are linked to the B-genome of Musa. We also provide evidence that cv. Williams (Musa AAA group) contains a distinct badnavirus integrant that is closely related to the ‘dead’ virus integrant previously characterized from Calcutta 4 (Musa acuminata ssp. burmannicoides). Our results suggest that the virus integrant from cv. Williams is linked to the A-genome, and the complexity of the hybridization patterns suggest multiple sites of integration and/or variation in sequence and structure of the integrants.     

Plague Meningitis—A Retrospective Analysis of Cases Reported in the United States, 1970-1979

Meningitis caused by Yersinia pestis developed in 6 (6%) of a total of 105 patients with plague reported to the Centers for Disease Control from 1970 to 1979. Five of the six cases occurred in children aged 10 to 15 years. All six patients received antibiotic therapy before meningitis developed, which appeared between the 9th and 14th days after the onset of acute illness in five of the six patients. There were no neurologic sequelae. The antigenic and biochemical profiles of the Y pestis strains isolated from cerebrospinal fluid in the meningitis cases did not differ from those of the Y pestis strains obtained from blood and bubo aspirates in the other 99 patients, and neither did in vitro studies suggest antibiotic resistance. While plague meningitis is an uncommon complication of acute plague infection, physicians in the western United States should be aware that it may develop as much as 14 days after antibiotic therapy for the acute plague infection has been initiated.     

Embryo transfer as a means of controlling the transmission of viral infections. X. The in vivo exposure of zona pellucida-intact porcine embryos to swine vesicular disease virus

Two experiments involving the transfer of embryos from donors infected with swine vesicular disease virus (SVDV) to "clean" recipients were carried out. In Experiment 1, 47 embryos were collected from 4 SVDV-infected donors and transferred to 2 recipients that subsequently produced 10 piglets. All of the recipients and piglets remained seronegative for SVDV. In addition to the transfers, 10 embryos and 58 unfertilized eggs from the infected donors were assayed in vitro and found to be negative for SVDV infectivity. A fifth donor was also inoculated with SVDV in this experiment, but it could not be demonstrated that infection had occurred. This SVDV-exposed donor provided two embryos for transfer and one embryo and two unfertilized eggs for in vitro assay. In Experiment 2, 158 embryos from 9 infected donors were transferred to 7 recipients, resulting in 12 piglets. A total of 7 embryos and 37 unfertilized eggs were assayed in vitro. The recipients, piglets, and embryos/eggs were all negative for SVDV infectivity. Although a final conclusion on the safety of using embryo transfer for the control of swine vesicular disease (SVD) is not possible, the results obtained justify additional studies.     

Embryo transfer as a means of controlling the transmission of viral infections. IX. The in vitro exposure of zona pellucida-intact porcine embryos to swine vesicular disease virus

When zona pellucida-intact porcine embryos were exposed to 10(7) plaque-forming units (pfu)/ml of swine vesicular disease virus (SVDV) and then washed, infectious virus could be isolated from all of the embryos. Culturing the embryos for 24 or 48 h or treating the embryos with pronase, trypsin, or antiserum after virus exposure and washing reduced the number of embryos carrying virus and lessened the amount of virus on each of the embryos. None of the treatments, however, was capable of disinfecting every embryo.