Morphological change in the early stages of the mating process of Rhodosporidium toruloides.
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The events which occur in the early stages of the mating process of the yeast Rhodosporidium toruloides between strains M-919 (mating type A) and M-1057 (mating type a) were investigated. In preliminary experiments we determined the frequency of mating by two newly designed methods: the liquid culture method and the membrane-filter microculture method. The mating frequencies of strains M-919 and M-1057 were 89% in the liquid culture method and 62% in the membrane-filter microculture method. The early stages in the mating process included the following events: (i) M-919 cells produce constitutively the extracellular inducing substance (A factor), (ii) M-1057 cells receive A factor, and in response to it they form mating tubes and secrete another inducing substance (a factor), (iii) M-919 cells receive a factor, and in response to it they form mating tubes, (iv) mating tubes elongate to the cells or the tubes of mating partner, (v) tips of the growing tubes recognize the opposite mating type cells or their tubes, followed by cell-to-cell fusion. (+info)
Restriction of DNA in Yersinia enterocolitica detected by recipient ability for a derepressed R factor from Escherichia coli.
(26/410)
A derepressed R factor, RY2drd2, was transferred at a frequency of 5x10minus 3 between two strains of Yersinia enterocolitica mated on a membrane. Under the same conditions transfer of this R factor from Escherichia coli to Y. enterocolitica was observed at a frequency of only 7-7x10minus 6. This frequency was greatly increased when the recipient strain was heat-treated before mating. Heat exposure for optimum fertility was 50 to 52 degrees C for a period of 2 to 3 min. Mutants of Y. enterocolitica were isolated which were infected by RY2drd2 from E. coli or from Y. enterocolitica at the same frequency. These observations strongly suggest that a DNA restriction and modification system in Y. enterocolitica causes its low recipient ability for plasmids from other species. (+info)
Pfizer selective enterococcus agar overlay method for the enumeration of fecal streptococci by membrane filtration.
(27/410)
The use of Pfizer selective enterococcus (PSE) agar with the membrane filter technique for the enumeration of fecal streptococci is limited due to the inability of the characteristic black precipitate, indicative of esculin hydrolysis, to diffuse from the medium through the membrane. A modification of the membrane filter technique that consisted of placing the membrane on PSE agar and overlaying it with tempered PSE agar was evaluated by comparing recovery, selectivity, and other parameters with M-enterococcus and KF-streptococcus agars, two selective media routinely used with the membrane filter technique for the enumeration of fecal streptococci in water and wastewater. No statistically significant differences could be demonstrated in the recovery capabilities of the three media. Inasmuch as the PSE overlay technique requires only 24 h of incubation as opposed to 48 h for the other two media, this modification may have some merit in water pollution monitoring programs. (+info)
Enumeration of high numbers of bacteria using hydrophobic grid-membrane filters.
(28/410)
Printing a wax grid on a conventional membrane filter yields a device functioning as a most probable number apparatus (MPN), used at a single dilution but with a very large number of growth compartments (e.g., 3,650). By restraining the lateral spread and confluence of colonies, the hydrophobic grid-membrane filter (HGMF) allows growth- or colony-forming units (GU) to be resolved at levels far above those which produce an uncountable lawn on a conventional membrane filter. It also eliminates the size variation of normal bacterial colonies. As a result, the HGMF can give more accurate estimates of the concentration of GU. The method by which grid-cell count observations can be used to obtain MPN estimates of the number of GUs is described, and estimates obtained using the MPN method on the HGMF are compared with those resulting from conventional colony count procedures on membrane filters. A linear relation was observed between MPNGU and the number of GUs, at levels up to 30,000 GUs, for pure cultures of bacteria and for samples of natural waters. The HGMF has great potential for reducing the labor required in quantitative microbiology, since it allows, with one filter, enumeration of microorganisms over a very large concentration range and therefore reduces the need to make dilutions. (+info)
Optimum membrane structures for growth of coliform and fecal coliform organisms.
(29/410)
The purpose of this study was to determine the optimum membrane filter structure and characteristics for recovery of coliform organisms. Additionally, other factors such as sterilization method and membrane composition were examined. Fecal coliform growth tests with varied samples indicated that the most critical factor in recovery was surface pore morphology and not other factors previously suspected. Fecal coliform counts showed a dramatic increase, with increasing surface opening sizes. Membrane structures with surface openings large enough to surround the entrapped bacteria are required for optimum growth of fecal coliform organisms. Maximum fecal coliform recoveries are obtained using membranes composed of mixed esters of cellulose exhibiting a surface opening diameter of 2.4 mum and a retention pore size of 0.7 mum. (+info)
Comparison of the new millipore HC with conventional membrane filters for the enumeration of fecal coliform bacteria.
(30/410)
Fecal coliform recoveries were determined for six types of membrane filters using 65 nonchlorinated water samples. Results showed that the membranes could be ranked in order of decreasing recovery as follows: Millipore HC greater than Gelman greater than Johns-Manville approximately Sartorius greater than Millipore HA greater than Schleicher & Schuell. (+info)
Influence of coliform source on evaluation of membrane filters.
(31/410)
Four brands of membrane filters were examined for total and fecal coliform recovery performance by two experimental approaches. Using diluted EC broth cultures of water samples, Johns-Manville filters were superior to Sartorius filters for fecal coliform but equivalent for total coliform recovery. Using river water samples, Johns-Manville filters were superior to Sartorius filters for total coliform but equivalent for fecal coliform recovery. No differences were observed between Johns-Manville and Millipore or Millipore and Sartorius filters for total or fecal coliform recoveries using either approach, nor was any difference observed between Millipore and Gelman filters for fecal coliform recovery from river water samples. These results indicate that the source of the coliform bacteria has an important influence on the conclusions of membrane filter evaluation studies. (+info)
Evaluation of coli-count samplers for possible use in standard couting of total and fecal coliforms in recreational waters.
(32/410)
Millipore Coli-Count Samplers were used to enumerate colonies of laboratory cultureunts than standard membrane0filter procedures for both total and fecal coliforms. Althought the samplers are useful for semiquantitative analysis as indicated by the manufacturer, they are not suitable examinations of recreational waters. (+info)