The reactivity of aluminosilicate glasses in cements - effects of Ca content on dissolution characteristics and surface precipitation

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Genetic studies with klebsiella

(1) Numerous attempts were made to detect transformation of Klebsiella strains. In these experiments, DNA was extracted from donor bacteria by a variety of techniques, and the resulting preparations were applied to genetically marked recipient bacteria. In some cases the recipient cells had previously been treated with agents which were known to affect the integrity of the cell wall, and in other cases the recipient cells were taken from ordinary broth cultures. No evidence of transformation was obtained in any experiment; possible reasons for this finding are discussed.(2) Attempts were made to demonstrate lysogeny in Klebsiella aerogenes strain A3> but no positive results were obtained. Similarly, none of the other Klebsiella strains tested were found to release phages active on K. aerogenes strain A3.(3) Several bacteriophages were isolated from natural sources by the enrichment culture technique, with K. aerogenes strain A3 as host. Five of the phages were found to produce turbid zones of partial clearing when plated on strain A3, but none were found to be capable of lysogenising cells of strain A3(4) Attempts were made to transduce K. aerogenes strain A3 and genetically marked derivatives of this strain with a number of virulent phages. Several different methods of minimising superinfection by free phage were used, but no transductants were recovered in any experiment.(5) Auxotrophic mutants of lysogenic and sensitive indicator Klebsiella strains were prepared, and used in preliminary mixed cultivation experiments. The results suggested that genetic exchange had occurred in tests involving K. aerogenes strain W52(6) K. aerogenes strain W52 was found to be lysogenic, but did not appear to be ultraviolet inducible. However, cultures of strain W52 which had been treated with the potent mutagen N-methyl-N'-nitro-N-nitrosoguanidine were found to lyse and release large numbers of plaque-forming particles. This result suggests that NTG is an effective inducing agent, but the possibility that phage lysates obtained by NTGinduction would be unsuitable for use in transduction experiments is discussed.(7) The phage released by strain W52 was propagated in cells of a sensitive strain and designated PW52. Preliminary spot tests suggested that phage PW52 was capable of mediating transduction, with the important limitation that transductants were only recovered if the recipient bacteria were immune to lytic infection by the phage.(8) The characteristics of the system of genetic exchange which appeared to involve phage PW52 were studied, and although absolute confirmation was not obtained the results strongly suggested that phage PW52 was in fact capable _7 of mediating transduction at frequencies varying from 5 x 10 —9 to 3 x 10 per phage particle adsorbed. No evidence was found to suggest that any of the other known mechanisms of genetic exchange were involved in the system which was being studied.(9) It was found that non-mucoid mutants of K. aerogenes strains W52 and W70 could not be transduced with respect to any of the markers tested, and a possible reason for this finding is suggested.(10) Experiments were carried out to test for joint transduction of streptomycin resistance and maltose utilisation markers, but no positive results were obtained.(11) In further preliminary attempts to detect linkage of genetic markers, it was found that certain ade markers appeared to be cotransducible with a strr marker, but later experiments suggested that this result could be explained without postula¬ ting a specific joint transduction of the markers concerned.(12) Some 22 auxotrophic mutants of K. aerogenes strains W52 and W70 were isolated following treatment with N-methyl-N1- nitro-N-nitrosoguanidine, and used in a large series of trans¬ duction tests. The results of these experiments suggested several linkage relationships, which are discussed in some detail. One of the possible linkage relationships was partially confirmed by the donor phenotype selection technique, and several tests which might be expected to provide further confirmation are outlined.(13) Mixed cultivation experiments with auxotrophic derivatives of K. aerogenes strain A3 and K. pneumoniae strain 1.9 failed to yield any evidence of genetic recombination(14) Transfer of the F-lac episome from an E. coli K12 strain to a lac mutant of K. aerogenes strain A3 was observed, but the F-lac+ recombinants were not found capable of trans¬ ferring the episome to an F~lac~ strain of E. coli.(15) Attempts to detect transfer of the F factor from E. coli K12 to Klebsiella strains, or of chromosomal material from an Hfr strain of E. coli K12 to Klebsiella strains, were unsuccessful.(16) Attempts were made to demonstrate elimination of the genetic determinant of bacteriocinogeny from K. pneumoniae strain 1.2 by treatment with acridine dyes, but the results were negative. Experiments designed to detect transfer of the bacteriocin determinant from strain 1.2 to other Klebsiella strains failed to yield any evidence that the determinant was transmissible from cell to cell.(17) It was found that infectious drug resistance (R) factors could be transferred between Klebsiella strains, but transfer was always found to occur at low frequency. The mechanism of the genetic exchange was not characterised fully, but appeared to be a typical example of bacterial conjugation.(18) Experiments involving transfer of an R factor from a capsulate donor strain to capsulate and non-capsulate recipient strains were carried out. No evidence was found to suggest that the non-capsulate strains were capable of acquiring the R factor more efficiently than the capsulate strain.(19) The behaviour of Klebsiella strains in highfrequency resistance transfer systems was studied, and it was concluded that the strains used were not capable of acting as efficient recipients of R factors, and were probably poor donors as well.(20) An R factor which was no longer sensitive to a repressor of its conjugation functions was transferred to Klebsiella strains, and the R+ strains so obtained were used in attempts to detect transfer of chromosomal genetic material to an R~ Klebsiella strain. The R~ strain which was used had been found to act as a reasonably efficient recipient of the derepressed R factor alone, but no chromosomal recombinants were recovered.(21) Derivatives of K. aerogenes strain A3 carrying a derepressed R factor were found to be insensitive to the malespecific bacteriophage MS-2, and appeared to be unable to adsorb significant numbers of MS-2 particles. In control experiments, an E. coli K12 strain carrying the same factor was found to be sensitive to phage MS-2 and capable of removing some 75$ of the MS-2 particles from a culture supernatant

The Effect of Interfacial Chemical Bonding in TiO2-SiO2 Composites on their Photocatalytic NOx Abatement Performance

The authors gratefully acknowledge funding from the UK Engineering and Physical Sciences Research Council (Grant Ref: EP/M003299/1) and the Natural Science Foundation of China (No. 51461135005) International Joint Research Project (EPSRC-NSFC).Peer reviewedPublisher PD

Photocatalyst efficiencies in concrete technology : the effect of photocatalyst placement

The authors gratefully acknowledge funding from the UK Engineering and Physical Sciences Research Council (Grant Ref: EP/M003299/1) and the Natural Science Foundation of China (No. 51461135005, No. 51478370) International Joint Research Project (EPSRC-NSFC).Peer reviewedPublisher PD

The effect of hydrogen sulphide on ammonium bisulphite when used as an oxygen scavenger in aqueous solutions

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Putting stored hydrogen to work without consuming it : a flexible system for energy conversion and water desalination

Acknowledgements We gratefully acknowledge the ACEMAC facility’s cooperation in providing scanning tunnelling imaging and the continued support of the University of AberdeenPeer reviewe

Amblyrhiza and the Vertebrate Paleontology of Anguillean Caves

Recorded interest in the caves of Anguilla dates back to the second half of the nineteenth century. The earliest explorations were concerned with the locating phosphatic cave earths, and resulted in the mining of several sites. Incidental to this work, the bones of the largest island rodent ever discovered were collected from Aguillan caves. Whereas the phosphate mining operations were short-lived, the remains of the giant rodent Amblyrhiza have catalyzed a continued interest in the caves of Anguilla. The most recent series of explorations have provided the first adequate documentation of Amhlyrhiza fossil sites, and have started to yield radiometric dates

On the Underlying Mechanisms of the Low Observed Nitrate Selectivity in Photocatalytic NOx Abatement and the Importance of the Oxygen Reduction Reaction

The authors are grateful to the German Ministry of Economics for funding the AiF/IGF project 18152 N and to the European Commission for funding the European Project Light2CAT (grant agreement no. 283062) in which some of the results presented here were obtained.Peer reviewedPostprin

The Different Roles of Water in Photocatalytic DeNOx Mechanisms on TiO2 : A Basis for Engineering Nitrate Selectivity?

The authors gratefully acknowledge funding from the UK Engineering and Physical Sciences Research Council (Grant Ref: EP/M003299/1) and the Natural Science Foundation of China (No. 51461135005) International Joint Research Project (EPSRC-NSFC).Peer reviewedPostprin