A conjugation system initially discovered in fl-lactamase-producing gonococci mobilized small non-selftransmissible R plasmids encoding ,8-lactamase (penicillinase) production into other gonococci, Neisseria, and Escherichia coli. This conjugation system was mediated by a separate selftransmissible plasmid of 23.9 x 106 daltons, pFA2. Conjugative plasmids capable of mobilizing R plasmids were also found in nearly 8% of the non-penicillinase-producing gonococci. These were similar to pFA2 in size, buoyant density, and restriction endonuclease digest patterns but were less efficient than pFA2 in mobilization of the penicillinase plasmid pFA3. The presence of conjugative plasmids in gonococci isolated before the appearance of penicillinase-producing strains indicates that a conjugation system for plasmid transfer predated the appearance of R plasmids in gonococci.Recently, strains of Neisseria gonorrhoeae with plasmid-mediated ,f-lactamase (penicillin-278 on July 16, 2020 by guest

Cell‐cell interactions between genetically distinct bacteria, known as coaggregation, are important for the formation of mixed‐species biofilms such as dental plaque. Interactions lead to gene regulation in the partner organisms that may be critical for adaptation and survival in mixed‐species biofilms. Here, gene regulation responses to coaggregation between Streptococcus gordonii and Fusobacterium nucleatum were studied using dual RNA‐Seq. Initially, S. gordonii was shown to coaggregate strongly with F. nucleatum in buffer or human saliva. Using confocal laser scanning microscopy and transmission electron microscopy, cells of different species were shown to be evenly distributed throughout the coaggregate and were closely associated with one another. This distribution was confirmed by serial block face sectioning scanning electron microscopy, which provided high resolution three‐dimensional images of coaggregates. Cell‐cell sensing responses were analysed 30 minutes after inducing coaggregation in human saliva. By comparison with monocultures, 16 genes were regulated following coaggregation in F. nucleatum whereas 119 genes were regulated in S. gordonii. In both species, genes involved in amino acid and carbohydrate metabolism were strongly affected by coaggregation. In particular, one 8‐gene operon in F. nucleatum encoding sialic acid uptake and catabolism was up‐regulated 2‐ to 5‐fold following coaggregation. In S. gordonii, a gene cluster encoding functions for phosphotransferase system‐mediated uptake of lactose and galactose was down‐regulated up to 3‐fold in response to coaggregation. The genes identified in this study may play key roles in the development of mixed‐species communities and represent potential targets for approaches to control dental plaque accumulation.

Plasmid deoxyribonucleic acid from Neisseria gonorrhoeae containing a 7.1kilobase (kb) (4.7-megadalton) penicillinase (Pcr) plasmid transformed homogenic gonococci to penicillinase production at a low frequency. About 25% of the penicillinase-producing gonococcal transformants contained Pc' plasmids which were either larger or smaller than the 7.1 kb donor plasmid; these Pcr plasmids varied in size from 3.45 to 42 kb. Some of these altered plasmids differed from the donor plasmid in stability or in frequency of mobilization by a 36-kb (24-megadalton) conjugative plasmid. A restriction endonuclease cleavage map of the 7.1kilobase Pcr plasmid and several of the smaller deleted plasmids was constructed. The most common size of altered Pc' plasmid was 5.1 kb (3.4 megadaltons). A Pc' plasmid isolated from a gonococcus in London, England, was identical with these 5.1-kb transformant plasmids in both size and restriction endonuclease cleavage profiles, suggesting that the 5.1-kb pcr plasmid could have arisen from a 7.1-kb Pcr plasmid by a transfonnation-associated deletion in nature.

Many oral bacteria form macroscopic clumps known as coaggregates when mixed with a different species. It is thought that these cell-cell interactions are critical for the formation of mixed-species biofilms such as dental plaque. Here, we assessed the impact of coaggregation between two key initial colonizers of dental plaque, Streptococcus gordonii and Veillonella parvula , on gene expression in each partner. These species were shown to coaggregate in buffer or human saliva. To monitor gene regulation, coaggregates were formed in human saliva and, after 30 minutes, whole-transcriptomes were extracted for sequencing and Dual RNA-Seq analysis. In total, 272 genes were regulated in V. parvula , including 39 genes in oxidoreductase processes. In S. gordonii , there was a high degree of inter-sample variation. Nevertheless, 69 genes were identified as potentially regulated by coaggregation, including two phosphotransferase system transporters and several other genes involved in carbohydrate metabolism. Overall, these data indicate that responses of V. parvula to coaggregation with S. gordonii are dominated by oxidative stress-related processes, whereas S. gordonii responses are more focussed on carbohydrate metabolism. We hypothesize that these responses may reflect changes in the local microenvironment in biofilms when S. gordonii or V. parvula immigrate into the system.