Multiple Mating Types of <i>Mycobacterium smegmatis</i>

Mizuguchi, Yasuo; Suga, Kiyoko; Tokunaga, Tohru

doi:10.1111/j.1348-0421.1976.tb01009.x

Cited by 44 publications

(22 citation statements)

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“…S1 in the supplemental material). ISMs6110 was not detected in any of these isolates, which included two recipient strains (strains Jucho and Takeuchi) and three donor strains (strains mc 2 155, Rabinowitchi, and Nishi) (13). Thus, ISMs6110 is unique to the recipient strain MKD8; its absence in other M. smegmatis isolates is a strong indication that MKD8 acquired the element relatively recently.…”

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confidence: 90%

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IS 6110 , a Mycobacterium tuberculosis Complex-Specific Insertion Sequence, Is Also Present in the Genome of Mycobacterium smegmatis , Suggestive of Lateral Gene Transfer among Mycobacterial Species

2008

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IS6110 is an insertion element found exclusively within the members of the Mycobacterium tuberculosis complex (MTBC), and because of this exclusivity, it has become an important diagnostic tool in the identification of MTBC species. The restriction of IS6110 to the MTBC is hypothesized to arise from the inability of these bacteria to exchange DNA. We have identified an IS6110-related element in a strain of Mycobacterium smegmatis. The presence of IS6110 indicates that lateral gene transfer has occurred among mycobacterial species, suggesting that the mycobacterial gene pool is larger than previously suspected.Genetic exchange is thought to be a driving force behind the ability of bacterial species to evolve and adjust to environmental challenges. Lateral gene transfer (LGT) in bacteria is mediated by one of three processes, namely, conjugation, transformation, or transduction; examples of these processes have been described for almost all bacterial species (9,19). By contrast, the Mycobacterium tuberculosis complex (MTBC) species, comprising M. tuberculosis, M. africanum, M. bovis, M. cannetti, M. caprae, M. microti, and M. pinnipedi (10, 15), are clonal populations evolved from a single progenitor species that has diversified by the acquisition of spontaneous mutations rather than by LGT. Genome comparisons between these seven species show that they have almost identical 16S rRNA sequences and highly similar genome sequences, and there is no strong evidence for genetic exchange (Ͼ99% identity [2,3,16]). The lack of clearly documented LGT among members of the MTBC is thought to be a consequence of the organisms' solitary lifestyles within their hosts, preventing their contact with other mycobacterial species, or perhaps even other bacteria. Thus, it has become generally accepted within the scientific community that the MTBC species do not undergo genetic exchange (10,15,16).IS6110 is an insertion element that is found exclusively within the MTBC; the assumption has been that this restriction is a result of the lack of genetic exchange with other mycobacterial species. A benefit of this exclusivity is that IS6110 has become an important diagnostic tool in the differentiation of MTBC species from other mycobacteria. Moreover, the element's presence in multiple copies, and at differing locations in the genome, has provided an excellent method by which strains can be genotyped; because of these characteristics, IS6110 has been used extensively for epidemiological studies (12,18,20).Our studies have focused on DNA transfer between strains of M. smegmatis. This work has shown that DNA transfer occurs by a process most similar to conjugation: distinct donor and recipient strains exist and transconjugants are detected only after prolonged cell-cell contact (14,21,22). The transfer process is chromosomally encoded and can occur only from a donor to a recipient. The donor and recipient strains are independent isolates of M. smegmatis with distinct colony morphologies (13). The genetic basis for donor and recipient abilit...

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confidence: 90%

“…The transfer process is chromosomally encoded and can occur only from a donor to a recipient. The donor and recipient strains are independent isolates of M. smegmatis with distinct colony morphologies (13). The genetic basis for donor and recipient ability is unknown.…”

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confidence: 99%

IS 6110 , a Mycobacterium tuberculosis Complex-Specific Insertion Sequence, Is Also Present in the Genome of Mycobacterium smegmatis , Suggestive of Lateral Gene Transfer among Mycobacterial Species

2008

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“…2). The recipient strain, MKD8, is an independent isolate of M. smegmatis (27), and thus it is not a simple biofilm mutant derivative of mc 2 155. The introduction of pPR23lsr2 into MKD8 did not confer the ability to form a biofilm (data not shown), ruling out the possibility that MKD8 carries a defective lsr2 gene.…”

Section: Resultsmentioning

confidence: 99%

Mycobacterial Biofilms Facilitate Horizontal DNA Transfer between Strains ofMycobacterium smegmatis

et al. 2010

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Conjugal transfer of chromosomal DNA between strains of Mycobacterium smegmatis occurs by a novel mechanism. In a transposon mutagenesis screen, three transfer-defective insertions were mapped to the lsr2 gene of the donor strain mc 2 155. Because lsr2 encodes a nonspecific DNA-binding protein, mutations of lsr2 give rise to a variety of phenotypes, including an inability to form biofilms. In this study, we show that efficient DNA transfer between strains of M. smegmatis occurs in a mixed biofilm and that the process requires expression of lsr2 in the donor but not in the recipient strain. Testing cells from different strata of standing cultures showed that transfer occurred predominantly at the biofilm air-liquid interface, as other strata containing higher cell densities produced very few transconjugants. These data suggest that the biofilm plays a role beyond mere facilitation of cell-cell contact. Surprisingly, we found that under standard assay conditions the recipient strain does not form a biofilm. Taking these results together, we conclude that for transfer to occur, the recipient strain is actively recruited into the biofilm. In support of this idea, we show that donor and recipient cells are present in almost equal numbers in biofilms that produce transconjugants. Our demonstration of genetic exchange between mycobacteria in a mixed biofilm suggests that conjugation occurs in the environment. Since biofilms are considered to be the predominant natural microhabitat for bacteria, our finding emphasizes the importance of studying biological and physical processes that occur between cells in mixed biofilms.Biofilms are dynamic communities of microorganisms that form on surfaces or at air-liquid interfaces (17,20,41). They arise following the attachment of bacteria to a surface; the bacteria then grow, differentiate, and multiply. The colonizing bacteria produce extracellular polymers, which encapsulate the cells and trap particulate matter, nutrients, and other bacteria that in turn contribute to the further development of the biofilm. Thus, as the biofilm develops it becomes increasingly heterogeneous. Microbial life is thought to exist predominantly in a biofilm, and biofilms can have either beneficial or harmful impacts on their environments (23). From a medical standpoint, biofilms can create serious problems. Bacteria within a biofilm are inherently more resistant to antibiotics, which makes their eradication difficult and is particularly problematic for patients with surgical implants resulting in chronic infections (19,33).Mycobacteria are known to form biofilms; however, relatively little is known about the mechanism of biofilm formation and development or its role in the biology of Mycobacterium species. For practical reasons, most biofilm studies have focused on the more rapidly growing and less pathogenic species, namely, Mycobacterium fortuitum, M. marinum, and M. smegmatis (16, 18, 36). In particular, genetic studies of M. smegmatis have provided insight into some of the key factors required f...

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“…There is a faint similarity of our mating system to the mating types of Nocardia opaca (Brownell, 1978) and of Mycobacterium smegmatis (Mizuguchi et al, 1976) with respect to the spectra of recipients giving fertile mating with the wild type and the transconjugants as donors ( Table 5). These phenomena can not yet be explained.…”

Section: Discussionmentioning

confidence: 99%

Hydrogen Autotrophy as a Transferable Genetic Character of Nocardia opaca 1b

Reh¹,

Schlegel²

1981

Microbiology

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~ ~A mating system to transfer the ability of growing autotrophically as a hydrogen bacterium (aut+ marker) has been developed in Nocardia opaca strain lb. Following filter mating between an aut+trp str strain and an aut strain, transconjugants of the phenotype Aut+Trp+StrS were obtained. The number of recombinant colonies exceeded the number of revertants by a factor of lo5. This and other crosses indicated that only the aut+ marker is transferred. Among other markers tested (growth on lactate and benzoate) no new combinations were found. A few strains of the Rhodococcus taxon were tested for their ability to act as recipients. Transconjugants of R hodococcus erythropolis and Corynebacteriurn hydrocarboclastus able to grow autotrophically were isolated. Most transconjugants were able to act as aut+ donors, but with different recipient spectra. As indicated by the observation of sectored colonies after autotrophic growth, by the measurement of the frequency of loss of autotrophy compared to auxotrophic markers, and by the effect of mitomycin C treatment, the aut+ marker does not become integrated in the recipient chromosome in a stable state. It is probably located on a plasmid.

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Multiple Mating Types of Mycobacterium smegmatis

Abstract: Multiple mating systems were found in the strains of Mycobacterium smegmatis.

Cited by 44 publications

References 16 publications

IS 6110 , a Mycobacterium tuberculosis Complex-Specific Insertion Sequence, Is Also Present in the Genome of Mycobacterium smegmatis , Suggestive of Lateral Gene Transfer among Mycobacterial Species

IS 6110 , a Mycobacterium tuberculosis Complex-Specific Insertion Sequence, Is Also Present in the Genome of Mycobacterium smegmatis , Suggestive of Lateral Gene Transfer among Mycobacterial Species

Mycobacterial Biofilms Facilitate Horizontal DNA Transfer between Strains ofMycobacterium smegmatis

Hydrogen Autotrophy as a Transferable Genetic Character of Nocardia opaca 1b

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