Cloning of nisin resistance determinant and replication origin on 7.6-kilobase EcoRI fragment of pNP40 from Streptococcus lactis subsp. diacetylactis DRC3

The nisin resistance determinant and an origin of replication on pNP40, a plasmid of about 60 kilobases that is present in Streptococcus lactis subsp. diacetylactis DRC3, was cloned on a 7.6-kilobase EcoRI fragment. When self-ligated, this fragment existed as an independent replicon (pFM011) and contained a 2.6-kilobase EcoRI-XbaI fragment encoding nisin resistance.     

Co-segregation of a gene encoding a deletion ligand for Tcrb-V3+ T cells with Mtv-3

A gene encoding the endogenous superantigen Mls^c, which deletes Tcrb-V3⁺ T cells in the NOD inbred mouse strain, was found to co-segregate with Mtv-3 on chromosome 11. This identifies a fourth gene encoding a deletion ligand for Tcrb-V3⁺ T cells and extends recently published observations in support of the hypothesis that a number of endogenous superantigens are the products of Mtv proviruses. Address correspondence and offprint requests to : K. Tomonari.     

Extracellular ß-galactosidase production during growth of filamentous fungi on polygalacturonic acid

The ß-galactosidase enzymes of Aspergillus oryzae and Scopulariopsis sp. are secreted during growth of the fungi on polygalacturonic acid, but not during growth on a wide range of other substrates, including lactose. The enzymes are thermotolerant with temperature optima in the range 55–65°C. The results indicate that fungal extracellular ß-galactosidases are involved in fungal growth on complex polysaccharides but not on lactose.     

Rapid determination of antimicrobial susceptibility patterns ofListeria monocytogenes isolates by the autobac AIS and MIC procedures

A total of 34 isolates ofListeria monocytogenes were tested against ampicillin, cephalothin, chloramphenicol, erythromycin, tetracycline, and penicillin-G using the Autobac 3-h AIS and the Autobac 5-h MIC procedures. The results were compared to susceptibility category interpretations and MICs determined using the Sceptor system. With the Sceptor System, all isolates were interpreted to be moderately susceptible to ampicillin and penicillin-G, and susceptible to the four other antibiotics. With the Autobac AIS, all isolates were interpreted to be susceptible to all the antibiotics except penicillin-G. All but one of the 34 isolates were interpreted to be resistant to penicillin-G with the Autobac AIS test. The remaining isolate was interpreted to be indeterminant. The Autobac AIS test was unsatisfactory for determining the susceptibility ofL. monocytogenes isolates to penicillin-G. The Autobac MIC results correlated well with the MIC results of the Sceptor system provided that the Autobac was programmed as though it were testing enterococci. The Autobac MIC reported penicillin-G MICs in units per milliliter and required the use of a conversion factor to obtain micrograms per milliliter, and did not allow for the testing of erythromycin. The Autobac MIC susceptibility category interpretations must not be used, as they were derived from an outdated susceptibility standard. The Autobac MIC test may be used if the limitations given above are observed.     

DNA-DNA homology among lactose- and sucrose-fermenting transconjugants from Lactococcus lactis strains exhibiting reduced bacteriophage sensitivity.

DNA-DNA homology between a reduced bacteriophage sensitivity (Rbs+) probe and DNA from both Rbs+ and Rbs- Lactococcus lactis strains was examined. Homology was detected between the probe and five plasmids (pCI750, pCC34, pEB56, pNP2, and pJS88) isolated from lactose-positive Rbs+ transconjugants and between the probe and genomic DNA of a sucrose-positive Rbs+ transconjugant. Additionally, hybridizations conducted between the probe and plasmids reported to encode abortive bacteriophage infection indicated homology with pTR2030 but not with pBF61 and pGBK17. The results suggest that a common genetic determinant(s) may be present in a variety of lactococcal plasmids coding for Rbs+.     

Degradation of polygalacturonic acid by Saccharomyces cerevisiae

Thirty-three strains of Saccharomyces cereuisiae were tested for the ability to degrade polygalacturonic acid. Nine strains degraded polygalacturonic acid during growth in liquid or on solid medium supplemented with glucose. This ability of certain strains of S. cereuisiae may be important in the fermentation plant products.     

Antimicrobial activity of Enterococcus faecium against Listeria spp.

Listeria spp. have been isolated from vegetation, silage, the intestinal tracts of animals and foods such as milk and cheese. Lisleria spp. are taxonomically related to lactobacilli (Seeliger & Jones 1986) and some bacteriocins produced by lactic acid bacteria will inhibit growth of Listeria spp. Bacteriocins such as nisin from Lactococcus lactis and pediocin A from Pediococcus pentosoreus, are active against microorganisms from several Gram-positive genera, and will inhibit L. monocytogenes. Bacteriocins (e.g. helveticin J and lactacin F) which only inhibit strains closely related to the producing micro-organism are not effective against L. monocytogenes     

Isolation of single taste cells from lingual epithelium

A method is described for obtaining large numbers of isolatedtaste cells with identified polarity from lingual epithelium.The procedure involves incubating lingual epithelium in collagenase,staining the apical surface with fluorescein-conjugated wheatgerm agglutinin (FTTC-WGA), peeling non-gustatory surface epitheliumfrom the underlying taste buds and connective tissue, and dissociatingisolated taste buds with Ca²⁺-free saline. Isolated taste cellsretain their characteristic morphology for at least 30 min afterdissociation, and the apical specialization can be identifiedas a single patch of fluorescence usually located at the tipof an elongate process. Isolated taste cells are amenable tostudy with the patch-clamp technique, and whole-cell patch-clamprecordings show that isolated taste cells have membrane propertiessimilar to taste cells of intact lingual epithelium. Evidenceis presented that FITC-WGA staining does not alter the voltage-dependentionic currents of the taste cell membrane.     

The cryptoendolithic microbial environment in the Ross Desert of Antarctica: Light in the photosynthetically active region

The vertical zonation of the Antarctic cryptoendolithic community appears to form in response to the light regime in the habitat. However, because of the structure of the habitat, the light regime is difficult to study directly. Therefore, a mathematical model of the light regime was constructed, which was used to estimate the total photon flux in different zones of the community. Maximum fluxes range from about 150m photons m^–2 s^–1 at the upper boundary of the community to about 0.1m photons m^–2 s^–1. Estimates of the annual productivity in the community indicate that the lowest zone of the community is light limited, with the maximal annual carbon uptake equivalent to less than the carbon content of one algal (Hemichloris) cell.