117538 186..199 Bibliometric tools applied to analytical articles: the example of gene transfer-related research Donghui Wen College of Environmental Sciences and Engineering, Peking University, Beijing, China, and Te-Chen Yu and Yuh-Shan Ho Bibliometric Research Centre, I-Shou University, Kaohsiung, Taiwan Abstract Purpose – The objective of this study is to conduct a bibliometric indicator and to conduct an analysis of citations per publication of all horizontal gene transfer-related publications in the Science Citation Index (SCI). A systematic search was performed using the SCI for publications during the period 1991-2005. Design/methodology/approach – The data were based on the online version of the Science Citation Index (SCI), Web of Science. Analyzed parameters included authorship, patterns of international collaboration, journal, language, document type, number of times cited, author, and KeyWords Plus. Findings – The USA and Germany produced 57 percent of the total articles and 77 percent of the total times cited in three years after publication. In addition, a simulation model was applied to describe the relationship between the cumulative number of citations and the article life. Originality/value – This is one of the first studies that uses analysis of citations per publication, defined as the ratio of the number of citations per publication in a certain period, to assess the impact relative to the entire field. Keywords Serials, Genetics, Research results, Publishing Paper type Research paper Introduction Horizontal gene transfer (HGT), or lateral gene transfer (LGT), is the collective name for processes that permit the exchange of DNA among organisms of different species (Jain et al., 2003). In the reproduction strategies of a replicon, vertical transfer of chromosome is the faithful way of increasing the genotype of a species, while horizontal transfer of transposon, plasmids or viruses provides the chance of creating a recombinant genotype by contributing to the genome of a neighbor recipient cell (Heinemann, 1998; Brown, 2003). The earliest mention of HGT can be traced to 1905, when Merechowsky suggested that the eukaryotic mitochondria and chloroplast originated when bacteria invaded the eukaryotic cell and were subsequently incorporated by it (Syvanen and Kado, 1998). In the 1950s, upon the previous attempts of demonstrating recombination between diverse species of bacteria, Baron et al. (1959) and Miyake and Demerec (1959) reported that high frequency of recombination (Hfr) strains of Escherichia coli could transfer genetic information to certain mutant strains of Salmonella typhimurium. Ochiai et al. The current issue and full text archive of this journal is available at www.emeraldinsight.com/1065-075X.htm OCLC 25,3 186 Received December 2008 Reviewed January 2009 Accepted January 2009 OCLC Systems & Services: International digital library perspectives Vol. 25 No. 3, 2009 pp. 186-199 q Emerald Group Publishing Limited 1065-075X DOI 10.1108/10650750910982575 (1959) discovered infectious multiple-antibiotic resistant plasmids in pathogenic bacteria. Theoretical implications of HGT began to grow from the view of evolution in the 1970s (Went, 1971; Hartman, 1984). By the mid-1980s, numerous mechanisms for natural HGT were firmly established in the range from bacteria to metazoans (Ochman and Selander, 1984; Erwin and Valentine, 1984; Syvanen, 1984, 1987). However, the name “horizontal gene transfer” did not appear in the title, abstract or keywords of a publication until 1983, when Aporpium was reported as an example of horizontal gene-transfer (Setliff, 1983). In the succeeding research history, with the advance of molecular biology, more and more available scientific evidence has indicated that HGT is a natural process among wild-type organisms of prokaryotes (Penalva et al., 1990; Di Giovanni et al., 1996; Eisen, 2000; Koonin et al., 2001) and eukaryotes (Penalva et al., 1990; Rosewich and Kistler, 2000; Andersson, 2003). Now, under increasing pressure from human society, HGT is detected frequently, related to the occurrence of resistance to herbicides (Ka and Tiedje, 1994; de Lipthay et al., 2001) or antibiotics (Penalva et al., 1990; Coffey et al., 1995; Shoemaker et al., 2001; Zolezzi et al., 2004), and the catabolic pathways for the degradation of synthetic compounds (Herrick et al., 1997; van der Meer et al., 1998; Top et al., 2002; Wilson and Metcalf, 2005). In this study, the authors attempted to analyze bibliometrically the HGT-related literature published in journals listed in SCI from 1991 to 2005, in order to provide insights into the characteristics of the HGT literature and identify patterns, tendencies, or irregularities that may exist in the literature. An indicator, citations per publication, was also applied in this study. Furthermore, this will provide a comprehensive evaluation of current HGT research. Methodology The data were based on the online version of the Science Citation Index (SCI), Web of Science. SCI is multidisciplinary database of the Institute for Scientific Information (ISI), Philadelphia, USA. One common way of conducting bibliometric research is to use the SCI database to trace the times each document has been cited (Hsieh et al., 2004). In the 2005 edition of the Journal Citation Reports (JCR), 6,088 journals are listed in the SCI. “Horizontal-gene-transfer” or “lateral-gene-transfer” were used as keywords to search titles, abstracts, and keywords to identify HGT-related publications from 1991 to 2005. Articles originating from England, Scotland, Northern Ireland and Wales were re-categorized as being from the UK. Collaboration type was determined by the address of each author, where the term “single country” was assigned if the researchers’ addresses were from the same country. The term “international collaboration” was designated to those articles that were co-signed by researchers from different countries. The information downloaded included names of authors, contact address, title, year of publication, keywords, times cited, subject categories of the journal, names of journals publishing the articles, and publisher information. The records were downloaded into spreadsheet software, and additional coding was performed manually for the number of authors, country of origin of the collaborators, and impact factors of the publishing journals. Impact factors were taken from the Journal Citation Report (JCR) published in 2005. To assess the visibility of an article, the authors used the number of times it was cited as an indicator. The number of times cited for an article, however, is highly Gene transfer- related research 187 correlated with the length of time since its publication. To adjust for that, a new variable was created (Chuang et al., 2007). Figure 1 shows the relationship between the average number of times cited per paper and the number of years since the paper’s publication for all HGT-related articles from 1991 to 2005. It shows that the frequency of being cited was highest in the second full year since publication, and began to decrease thereafter. To adjust for bias due to differences in the length of time since publication, a new variable, TC2 (times cited before year 2), instead of just times cited since publication, was used to assess the visibility of articles. A TC2 for the year 2003 would be the number of times being cited before 2006 for all articles published in 2003. Another variable CPP (citation per publication) for articles published in a particular year was calculated as TC2 divided by the number of articles published in that year. In some cases, the authors only discuss documents published in the period 1991-2003, since articles published after 2003 would not have TC2 and CPP values during the analyzing period, i.e. 1991-2005. Results and discussion Document type and language There were 1,549 HGT-related documents published from 1991 to 2005. The distribution of document types identified by ISI was analyzed as listed in Table I. For the period 1991-2003, journal article was the most frequent document type, 765 articles comprising 79 percent of total production with a CPP of 14, followed distantly by 173 reviews comprising 18 percent of total production with a CPP of 20. Editorial material, letters, meeting abstracts, corrections, reprints, bibliographies, news items, notes, and Figure 1. Citations per article by article life for 1,208 HGT-related articles from 1991 to 2005 OCLC 25,3 188 software reviews showed lesser significance than articles and reviews. As journal articles represented the majority of document types that were also peer-reviewed within this field, a total of 1,208 relevant articles in the period 1991 2005 was identified and analyzed. The percentage of reviews related with HGT (18 percent) was notably high, however, implying that the HGT research is much comprehensive. The concept of HGT provides a penetrating insight into many significant phenomena of life, such as evolution, adaptation, genetic modification, recombination, antibiotic resistance, conjugation, transduction, and transformation. The predominant language for all journal articles was English (99 percent); others were published in French, (four articles, 0.44 percent), German (two articles, 0.22 percent), and Chinese and Russian (one article, 0.11 percent), respectively. Garfield and Welljamsdorof (1992) reported that English is the main language of microbiology research, accounting for 90-95 percent of all SCI papers. In addition, it could be expected that English would be used more frequently because more journals listed in ISI were published in English. Chronological publication output There were 1,208 HGT-related articles published from 1991 to 2005. Table II shows that the number increased significantly from 1991 (12 articles) to 1997 (32 articles). After 1997 there was been a large increase, reaching 195 articles in 2004 and 248 articles in 2005. Table II also shows TC2 and CPP during the period 1991-2003. Only 765 articles had CPP values. The average CPP was 14. The lowest CPP was found in 1995 at 8.2, while the highest CPP occurred in 1997 at 27. Figure 2 also shows that CPP has fluctuated over the years and a peak appeared in the year 1997. The reason for this is that Kunst et al. (1997) published “The complete genome sequence of the Gram-positive bacterium Bacillus subtilis” in Nature, with a TC2 of 499. This article analyzed the complete genetic information of a bacterial strain, Bacillus subtilis, the best-characterized member of the Gram-positive bacteria. In its genome, many genes are involved in the synthesis of secondary metabolites including antibiotics, and a few prophages or remnants of prophages are contained, indicating that bacteriophage 1991-2005 1991-2003 Document type P P TC2 CPP Article 1,208 (78) 765 (79) 10,823 14 Review 282 (18) 173 (18) 3,378 20 Editorial material 28 (1.8) 18 (1.8) 173 10 Letter 16 (1.0) 10 (1) 136 14 Meeting abstract 28 (0.39) 3 (0.31) 0 0 Correction 3 (0.19) 1 (0.10) 0 0 Reprint 2 (0.13) 2 (0.21) 25 13 Bibliography 1 (0.065) 0 (0) 0 0 News item 1 (0.065) 1 (0.10) 0 0 Note 1 (0.065) 1 (0.10) 13 13 Software review 1 (0.065) 0 (0) 0 0 Total 1,549 974 14,548 15 Notes: Figures in parentheses are percentages. P, number of papers; TC2, times cited before the second full year since publication; CPP, citation per publication Table I. Document distributions from 1991 to 2005 with CPP from 1991 to 2003 Gene transfer- related research 189 Year No. of articles TC2 CPP ICA 1991 12 199 17 3 (25) 1992 11 110 10 4 (36) 1993 16 176 11 7 (44) 1994 24 236 10 3 (13) 1995 27 222 8 4 (15) 1996 35 320 9 8 (23) 1997 32 871 27 6 (19) 1998 53 566 11 13 (25) 1999 67 1,177 18 17 (25) 2000 87 1,277 15 22 (25) 2001 114 2,171 19 38 (33) 2002 128 1,454 11 37 (29) 2003 159 2,044 13 30 (19) 2004 195 60 (31) 2005 248 79 (32) Total 1,208 331 (27) Notes: Figures in parentheses are percentages. TC2, times cited before the second full year since publication; CPP, citation per publication; ICA, international co-authorship Table II. Article characteristics by year of publication Figure 2. Relationships among the number of articles, citation per articles, and year OCLC 25,3 190 infection has played an important evolutionary role in horizontal gene transfer. Since its publication, this article was cited 1,633 times up to 2005 by 49 countries. Later, increasing studies of genes and genomes have indicated that considerable horizontal transfer has occurred between different species, leading to the steep increase in the number of HGT-related articles published after 1997. International collaboration Of the 1,208 articles, 331 articles, or about 27 percent, had international co-authorship (ICA). The annual percentage of articles with ICA is listed in Table II. The percentage of ICA articles was highest in 1993 at 44 percent, followed by 1992 at 36 percent, and 2005 at 32 percent. In general, ICA articles were more prevalent in recent years than earlier years. Using five-year intervals, the percentages of articles with ICA were 23 percent, 24 percent, and 29 percent for the periods 1991-1995, 1996-2000, and 2001-2005, respectively. It has been reported that the European Union is becoming more important as a scientific collaboration partner of both advanced and developing countries (Glänzel et al., 1999). In the case of stroke-related research in Taiwan, international co-authorship also increased. The percentages of articles with ICA were 14 percent, 17 percent, and 23 percent for the periods 1991-1995, 1996-2000, and 2001-2005, respectively (Chuang et al., 2007). Table III lists the ten most productive countries in total publications between 1991 and 2003, with ICA and CPP values. Among the 765 articles with CPP information from 1991 to 2003, international articles comprised 25 percent of the articles with a CPP of 29, compared to 75 percent from single countries, with a CPP of 13. International collaboration is a factor that attracts citations (de Granda Orive et al., 2007). The most highly cited European papers were found to be the multinational papers (Narin et al., 1991). The CPP values of the numbers of articles with international co-authorship were increased and significantly higher in the case of stroke-related research in Taiwan (Chuang et al., 2007). Horizontal gene transfer-related articles with ICA had significantly higher CPP values. It would be reasonable to assume that more international collaboration would lead to more output due to the sharing of ideas and workloads (Chuang et al., 2007). Meanwhile, single-country articles were produced by authors from 36 different countries, with the majority originating from the USA (192; 34 percent) with a CPP of 18 followed by Country SP CPP CP CPP TP CPP USA 192 (34) 18 97 (51) 24 289 (38) 20 Germany 85 (15) 11 61 (32) 27 146 (19) 18 UK 46 (8.0) 10 38 (20) 26 84 (11) 18 France 34 (5.9) 16 30 (16) 36 64 (8.4) 25 Canada 34 (5.9) 12 25 (13) 13 59 (7.7) 13 Japan 30 (5.2) 18 10 (5.2) 54 40 (5.2) 27 The Netherlands 11 (1.9) 7.9 16 (8.3) 44 27 (3.5) 29 Sweden 17 (3.0) 10 10 (5.2) 10 27 (3.5) 10 Spain 13 (2.3) 7.4 13 (6.8) 47 26 (3.4) 27 Australia 14 (2.4) 10 12 (6.3) 12 26 (3.4) 11 Notes: Figures in parentheses are percentages. SP, single country publications; CP, international collaborative publications; TP, total publications; CPP, citation per publication Table III. Ten most productive countries in total publications from 1991 to 2005 Gene transfer- related research 191 Germany (85; 15 percent) with a CPP of 11. Twenty countries contributed only one or two single-country articles. The country with the most international co-authorship was also the USA with 97 articles, comprising 51 percent of the total number of internationally co-authored articles, with an average CPP of 24. Germany was the country with the second greatest number of international collaborations, with 61 articles and an average CPP of 27. Nineteen countries contributed only one or two international collaborative articles. ICA articles with the highest TC2 values (Kunst et al., 1997) were co-authored with researchers from France, Japan, Germany, The Netherlands, the UK, the USA, Poland, and Ireland. In addition, the USA was the most productive and cited country in patent ductus arteriosus treatments (Hsieh et al., 2004), asthma in children (Chen et al., 2005), biomedicine (Figueredo et al., 2003), ophthalmic reserach (Ohba, 2005), and otolaryngology research (Cimmino et al., 2005). Journals and subject categories The 765 articles with CPP were published in 213 journals during 1991 to 2003. Table IV shows the ten most published names of journals, the number of articles published by these journals, CPP, ranking order of CPP, IF, and ranking order of IF in a subject category. The journal that published the greatest number of articles was Journal of Bacteriology, with 53 articles, followed by Proceedings of the National Academy of Sciences of the United States of America, and Journal of Molecular Evolution. The 48 articles published in Proceedings of the National Academy of Sciences of the United States of America had the highest CPP (31) and the highest IF (10.231) among the top ten journals. The 765 articles with subject category and CPP information were included in 58 subject categories. In the research history, HGT and recombination between two streptococcal lineages was first reported in the subject category of immunology and infectious diseases (Simpson et al., 1992); later, the horizontal transfer of bacterial heavy metal resistance genes was first presented in the subject category of environmental-related fields (Dong et al., 1998). Today, researchers in a number of unrelated fields are making observations related to HGT, leading to an unusual breadth of topics. Table V shows categories that had at least ten articles. The three top categories with the largest number of articles were Microbiology (279), Biochemistry & Molecular Biology (223), and Genetics & Heredity (180). All numerical analyses used integer counts, i.e. if an article was included in two or more different subject categories, each subject category was counted once, and thus in these instances the percentage will add up more than 100 percent. Distribution of KeyWords Plus KeyWords Plus provides search terms extracted from the titles of papers cited in each new article listed in the database in ISI (Garfield, 1990). KeyWords Plus substantially augments title-word and author-keyword indexing. Examination of KeyWords Plus revealed that 2,740 keywords were used in the 754 articles. Among them, 1,946 keywords (71 percent) appeared only once, 355 keywords (13 percent) appeared twice, and 134 keywords (4.9 percent) appeared three times. The large numbers of once-only keywords are caused by a wide disparity in research focus (such as “DNA gyrase”, “nitrogen-fixation”, “methane”, “rhizobium”, and “human skin”), a special material used in research (such as “Bacillus sphaericus”, “lacteriophage T7”, “L12” and “ribulose OCLC 25,3 192 Jo u rn a l A rt ic le C P P R a n k in g o f C P P S u b je ct ca te g o ry IF R a n k in g Jo u rn a l o f B a ct er io lo g y 5 3 (6 .9 ) 1 2 4 1 M ic ro b io lo g y 4 .1 6 7 1 6 /8 6 P ro ce ed in g s o f th e N a ti o n a l A ca d em y o f S ci en ce s o f th e U n it ed S ta te s o f A m er ic a 4 8 (6 .3 ) 3 1 7 M u lt id is ci p li n a ry sc ie n ce s 1 0 .2 3 1 3 /4 8 Jo u rn a l o f M o le cu la r E v o lu ti o n 4 1 (5 .4 ) 9 .2 5 7 B io ch em is tr y a n d m o le cu la r b io lo g y 2 .7 0 3 1 0 8 /2 6 1 E v o lu ti o n a ry b io lo g y 1 3 /3 3 G en et ic s a n d h er ed it y 5 9 /1 2 4 M o le cu la r B io lo g y a n d E v o lu ti o n 3 6 (4 .7 ) 1 3 3 9 B io ch em is tr y a n d m o le cu la r b io lo g y 6 .2 3 3 3 2 /2 6 1 E v o lu ti o n a ry b io lo g y 4 /3 3 G en et ic s a n d h er ed it y 1 5 /1 2 4 A p p li ed a n d E n v ir o n m en ta l M ic ro b io lo g y 3 0 (3 .9 ) 1 2 4 4 B io te ch n o lo g y a n d a p p li ed m ic ro b io lo g y 3 .8 1 8 2 1 /1 3 9 M ic ro b io lo g y 1 9 /8 6 F E M S M ic ro b io lo g y L et te rs 2 4 (3 .1 ) 5 .7 9 9 M ic ro b io lo g y 2 .0 5 7 5 3 /8 6 G en e 2 3 (3 .0 ) 8 .0 6 9 G en et ic s a n d h er ed it y 2 .6 9 4 6 0 /1 2 4 M o le cu la r M ic ro b io lo g y 2 2 (2 .9 ) 1 4 3 6 B io ch em is tr y & m o le cu la r b io lo g y 6 .2 0 3 3 3 /2 6 1 M ic ro b io lo g y 1 1 /8 6 In fe ct io n a n d Im m u n it y 2 0 (2 .6 ) 1 1 4 8 Im m u n o lo g y 3 .9 3 3 2 2 /1 1 5 In fe ct io u s d is ea se s 8 /4 3 M ic ro b io lo g y- S G M 1 8 (2 .4 ) 7 .8 7 0 M ic ro b io lo g y 3 .1 7 3 2 1 /8 6 N o te s : F ig u re s sh o w n in p a re n th es es a re p er ce n ta g es . C P P , ci ta ti o n s p er p u b li ca ti o n p u b li sh ed in re sp ec ti v e jo u rn a ls ; IF , im p a ct fa ct o r o f th e jo u rn a l in 2 0 0 5 Table IV. Core journals publishing horizontal gene transfer-related articles Gene transfer- related research 193 1,5-bisphosphate carboxylase”), or a combination of some general topics, such as “DNA-sequence data”, “microbial gene identification” “evolutionary information”, “last common ancestor”, and “penicillin-resistant strains”. Table VI shows 19 KeyWords Plus keywords that appeared at least 30 times. The most frequently used keyword was “Escherichia coli”, appearing in 29 percent of 754 articles published in 1991-2003 with a CPP of 14. Other frequently used keywords were KeyWords Plus No. of articles Percent TC2 CPP Escherichia coli 221 29 3,143 14 Evolution 133 18 2,116 16 Sequence 118 16 1,629 14 Horizontal gene transfer 99 13 1,184 12 DNA 89 12 924 10 Identification 78 10 1,321 17 Expression 76 10 1,102 15 Nucleotide sequence 70 9.3 1,024 15 Bacteria 63 8.4 613 10 Gene 58 7.7 1,117 19 Cloning 54 7.2 631 12 Protein 53 7.0 1,149 22 Genes 49 6.5 1,055 22 Strains 47 6.2 560 12 Sequences 45 6.0 494 11 Genome 39 5.2 374 10 Bacillus subtilis 33 4.4 516 16 Proteins 32 4.2 557 17 Origin 31 4.1 567 18 Notes: TC2, times cited before the second full year since publication; CPP, citation per publication Table VI. Frequency of KeyWords Plus keywords used Subject category Article Percentage TC2 CPP Microbiology 279 36 2,537 9.1 Biochemistry and molecular biology 223 29 2,741 12 Genetics and heredity 180 24 2,073 12 Biotechnology applied microbiology 102 13 1,230 12 Evolutionary biology 97 13 1,013 10 Multidisciplinary sciences 75 9.8 3,587 48 Infectious diseases 43 5.6 457 11 Immunology 41 5.4 351 8.6 Cell biology 31 4.1 357 12 Biology 27 3.5 341 13 Plant sciences 24 3.1 176 7.3 Pharmacology and pharmacy 18 2.4 142 7.9 Virology 15 2.0 158 11 Biophysics 13 1.7 58 4.5 Ecology 12 1.6 89 7.4 Notes: TC2, times cited before the second full year since publication; CPP, citation per publication Table V. Number of articles and CPP by subject category OCLC 25,3 194 “evolution” at 18 percent, and followed by “sequence” at 16 percent, “horizontal gene-transfer” at 13 percent, and “DNA” 12 percent. The 53 articles with the KeyWords Plus keyword “protein” and the 49 articles with the KeyWords Plus keyword “genes” had the highest CPP (22) among the 19 keywords. In addition, “project”, “strands”, “terminators”, and “yeast artificial chromosomes” appeared once with the highest CPP of 499. Information regarding popular keywords is useful in understanding the research profile. “Escherichia-coli” is the most frequently used host bacterium in the HGT-related research. By “DNA” and “sequence” analysis, more evidence was found to show that “horizontal gene-transfer” might be an important driving force of “evolution”. Citation model For the period 1991-2003, the cumulative number of citations increased. In year of publication for all 765 articles, 969 citations were obtained, while three years after articles were published (including the year of publication), the cumulative number of citations (TC2) was 10,823. A model can be used to describe the relationship between the cumulative number of citations, C, and the article life, Y (Chiu and Ho, 2005). The model can be expressed as: C ¼ KY þ S; where K is the citation rate (number of times cited/year) and S is the visibility potential when a paper is published (number of times cited). Moreover, K is a measure of how quickly the “average article” in the field is cited. S shows how often the articles published in the field are cited in the year of publication. This model fitting suggested that there were sustained constant citations in each year. Figure 3 shows that significant correlations between the yearly cumulative number of citations and the article life were made for the years 1991-2003, with the model having high coefficients of determination (r 2 . 0:984). The results indicated that articles published in 2001 had the highest citation rate and visibility potential, followed by those published in 2003 and 1999, respectively (Table VII). In other words, 114 research articles published in 2001 had the highest impact potential and the greatest numbers of times cited each year after the articles were published. Conclusions Studies on HGT dealing with the SCI have increased during the past 15 years. Journal articles were the most frequent document type, with a lower citation per publication rate than reviews. The top three ranking countries in terms of total publication were the USA, Germany, and the UK. Articles with international co-authorship had higher visibility. Journals listed in the subject category of microbiology published the most articles. Journal of Bacteriology published the greatest number of articles. “Escherichia coli” was the most frequently used KeyWords Plus keyword. A linear model was successfully applied to describe the relationship between the cumulative number of citations and article life. Articles published in 2001 had the highest citation rate and visibility potential. The most frequently cited article was published in 1997 in Nature, which is the highest impact factor journal in the category of multidisciplinary sciences. Gene transfer- related research 195 References Andersson, J.O. (2003), “Evolution of glutamate dehydrogenase genes: evidence for lateral gene transfer within and between prokaryotes and eukaryotes”, BMC Evolutionary Biology, Vol. 3 No. 14. Baron, L.S., Carey, W.F. and Spilman, W.M. (1959), “Genetic recombination between Escherichia coli and Salmonella typhimurium”, Proceedings of the National Academy of Sciences of the United States of America, Vol. 45 No. 7, pp. 976-84. Year K (number of times cited/year) S (number of times cited) r 2 1991 71.7 61.2 0.984 1992 48.3 18.3 0.990 1993 77.6 42.0 0.981 1994 95.2 60.9 0.986 1995 93.5 64.5 0.980 1996 151 28.5 0.996 1997 395 71.3 0.996 1998 254 63.1 0.999 1999 514 152 0.998 2000 628 17.5 0.998 2001 940 274 0.999 2002 679 101 0.998 2003 933 116 0.987 Table VII. 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(1998), Horizontal Gene Transfer, Chapman & Hall, London. Top, E.M., Springael, D. and Boon, N. (2002), “Catabolic mobile genetic elements and their potential use in bioaugmentation of polluted soils and waters”, FEMS Microbiology Ecology, Vol. 42 No. 2, pp. 199-208. van der Meer, J.R., Werlen, C., Nishino, S.F. and Spain, J.C. (1998), “Evolution of a pathway for chlorobenzene metabolism leads to natural attenuation in contaminated groundwater”, Applied and Environmental Microbiology, Vol. 64 No. 11, pp. 4185-93. Went, F.W. (1971), “Parallel evolution”, Taxonomy, Vol. 20, pp. 197-226. Wilson, M.M. and Metcalf, W.W. (2005), “Genetic diversity and horizontal transfer of genes involved in oxidation of reduced phosphorus compounds by Alcaligenes faecalis WM2072”, Applied and Environmental Microbiology, Vol. 71 No. 1, pp. 290-6. Zolezzi, P.C., Laplana, L.M., Calvo, C.R., Cepero, P.G., Erazo, M.C. and Gomez-Lus, R. (2004), “Molecular basis of resistance to macrolides and other antibiotics in commensal viridans group streptococci and Gemella spp. and transfer of resistance genes to Streptococcus pneumoniae”, Antimicrobial Agents and Chemotherapy, Vol. 48 No. 9, pp. 3462-7. Further reading Vergidis, P.I., Karavasiou, A.I., Paraschakis, K., Bliziotis, I.A. and Falagas, M.E. (2005), “Bibliometric analysis of global trends for research productivity in microbiology”, European Journal of Clinical Microbiology & Infectious Diseases, Vol. 24 No. 5, pp. 342-5. About the authors Donghui Wen is an Associate Professor in the College of Environmental Sciences and Engineering, Peking University in China. Her research interests include environmental biotechnology and wastewater treatment. To link two research aspects, molecular methods were used to detect the distribution of target bacterium and gene, the micro-community structure, functional gene expression, and the behaviour of mobile genetic elements during the wastewater treatment in biological reactors. Te-Chen Yu obtained his first degree in School of Public Health (2004) from the Taipei Medical University, Taiwan. He is a Research Assistant at the Bibliometric & Research Centre, I-Shou University, Taiwan. His area of specialization is bibliometric and research study. Yuh-Shan Ho obtained his PhD (1995) at the University of Birmingham, UK. He has published 110 papers in refereed journals (which have attracted more than 3,500 citations). He is the Executive Editor of Journal of Environmental Protection Science and the Director of the Bibliometric & Research Centre, I-Shou University, Taiwan. His research interests are the adsorption process for water and wastewater treatment, and bibliometric studies. Yuh-Shan Ho is the corresponding author and can be contacted at: ysho@isu.edu.tw Gene transfer- related research 199 To purchase reprints of this article please e-mail: reprints@emeraldinsight.com Or visit our web site for further details: www.emeraldinsight.com/reprints