To define the relationship between H63T and other Legionella species further, a 584 bp portion of the mip gene and a 327 bp portion of the rnpB gene of H63T were sequenced as described previously (Kuroki et al., 2007; Lück et al., 2010; Ratcliff et al., 1998; Rubin et al., 2005; Yang et al., 2012). The European Working Group for Legionella Infections (EWGLI) Legionella mip gene sequence database was used to determine the similarity based on mip, and NCBI BLAST was used to determine similarity based on rnpB (Altschul et al., 1990; Fry et al., 2007). Similar to the 16S rRNA gene sequence analysis, the mip gene sequence of strain H63T was most similar to that of L. brunensis ATCC 43878T (85.49 %), followed by Legionella hackeliae ATCC 35250T (85.11 %), L. jamestowniensis ATCC 35298T (85.11 %), L. feeleii ATCC 35072T (83.95 %) and L. lansingensis ATCC 49751T (83.56 %). Based on analysis of rnpB sequences, strain H63T was again most similar to the type strain of L. brunensis (91.2 %), followed by the type strains of L. lansingensis (89.4 %), L. jamestowniensis (89.7 %), L. hackeliae (88.3 %) and L. feeleii (88.3 %). For phylogenetic analyses, the 16S rRNA, mip and rnpB sequences of type strains of Legionella species and the nearest other relative within the Legionellaceae, Coxiella burnetii, were obtained from GenBank (Benson et al., 2008). Trimmed sequences were aligned using the CLUSTAL W program (Larkin et al., 2007). Phylogenetic trees were inferred by the neighbour-joining method using TOPALI version 2 and edited using TreeView version 1.6.6 (Milne et al., 2009; Page, 1996). Phylogenetic analysis based on the consensus alignment of 16S rRNA, mip and rnpB gene sequences indicated that strain H63T is most closely related to L. brunensis, followed by the group of L. hackeliae and L. jamestowniensis (Fig. 1). The strength of the association was confirmed by bootstrap values ≥80 based on 100 replicates. For completeness, DNA–DNA hybridizations were performed comparing H63T with both L. hackeliae ATCC 35250T and L. jamestowniensis ATCC 35298T, because they were closely related according to the consensus tree. According to hybridization analysis, L. hackeliae ATCC 35250T was 8.0 % (±0.9) related to H63T when H63T DNA served as the probe and 31.7 % (±0.4) similar when H63T represented the covalent DNA. L. jamestowniensis ATCC 35298T was 10.1 % (±1.2) similar to H63T when H63T DNA was the probe and 7.7 % (±3.3) similar when H63T DNA was the covalent DNA. The topologies of the individual gene trees support the consensus assignment of H63T and L. brunensis as sister taxa (Figs S1–S3, available in IJSEM Online).
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Fig. 1.
Neighbour-joining tree showing relationships between strain H63T and all previously sequenced type strains of Legionella species based on the consensus sequence of the 16S rRNA, mip and rnpB loci. Bootstrap values greater than 50 (from 100 replicates) are shown. Coxiella burnetii RSA 493 was used as an outgroup. GenBank accession numbers of the individual sequences used to reconstruct the tree are provided in Figs S1–S3. Bar, 0.1 substitutions per nucleotide site.
To complete our genetic analysis, the DNA G+C content of H63T was determined through HPLC analysis performed by the Identification Service of the DSMZ. The DNA G+C content of H63T was 41.8 mol%, within the range of values reported for its neighbours (39.0–52.0 mol%; Table 1).
Using the slide agglutination test as described previously (Thacker et al., 1985), antigen from H63T did not react with antisera generated previously against the type strains of Legionella species, including sera raised against all of the nearest neighbours in the 16S rRNA gene tree as well as the type strains of L. jamestowniensis and L. hackeliae (Table S1).
Initially, we determined the phenotype of strain H63T by examining a set of 13 physiological traits that are standards for Legionella (Table 2) (Hookey et al., 1996). Like most members of the genus Legionella (Dennis et al., 1993; Edelstein et al., 2012; Hookey et al., 1996; Yang et al., 2012), including its nearest neighbours, H63T grew well at 37 °C on buffered charcoal yeast extract (BCYE) agar or in buffered yeast extract (BYE) broth and required supplementary cysteine for growth. Colonies of strain H63T on BCYE agar did not autofluoresce under UV light, distinguishing the strain from its neighbours L. erythra, L. dresdenensis, L. rubrilucens and L. birminghamensis (Table 2). The strain, like many other legionellae (Hookey et al., 1996) but unlike L. dresdenensis and L. birminghamensis, secreted a brown pigment upon entering stationary phase (Table 2) (Chatfield & Cianciotto, 2007). Tests for glucose fermentation, nitrate reduction, urease, catalase, gelatinase and oxidase were performed as described previously (Orrison et al., 1983; Weaver & Feeley, 1979) using stationary-phase bacteria obtained from BCYE agar. β-Lactamase and hippurate hydrolysis activities were assessed by disc assays (Becton Dickinson) as described previously (Kuroki et al., 2007). As expected of a member of the genus Legionella (Dennis et al., 1993; Weaver & Feeley, 1979; Yang et al., 2012), H63T was negative for glucose fermentation, nitrate reduction and urease activity (Table 2). However, the strain was positive for catalase, gelatinase, β-lactamase and hippurate hydrolysis (Table 2). The strongly positive hippurate hydrolysis test distinguished H63T from L. brunensis, L. londiniensis, L. jordanis, L. erythra, L. dresdenensis, L. rubrilucens and L. birminghamensis, and the presence of both gelatinase and β-lactamase differentiated H63T from L. feeleii. The fact that H63T was positive for hippurate hydrolysis and weakly positive for oxidase distinguishes it from L. hackeliae and L. jamestowniensis, the two other species that showed high similarity to H63T based on mip and rnpB sequences (Brenner et al., 1985).
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Table 2. Differential characteristics of strain H63T compared with its nearest neighbours based on 16S rRNA gene sequences
Strains: 1, L. cardiaca sp. nov. H63T (data from this study); 2, L. brunensis ATCC 43878T (unless indicated, data from Wilkinson et al., 1988); 3, L. londiniensis ATCC 49505T (Dennis et al., 1993); 4, L. jordanis ATCC 33623T (Cherry et al., 1982); 5, L. erythra ATCC 35303T (Brenner et al., 1985), 6, L. dresdenensis DSM 19488T (Lück et al., 2010); 7, L. rubrilucens ATCC 35304T (Brenner et al., 1985); 8, L. feeleii ATCC 35072T (Brenner et al., 1985); 9, L. pneumophila ATCC 33152T (Brenner et al., 1979); 10, L. birminghamensis ATCC 43702T (Wilkinson et al., 1987). Reactions are scored as follows unless indicated: +, positive; +W, weakly positive; −, negative; ±, variable; ND, no data available. All strains grow on BCYE at 37 °C but do not grow under these conditions without cysteine, and all strains grow in BYE at 37 °C. All strains are positive for catalase and are negative for glucose fermentation, nitrate reduction and urease activity.
Although we were able to detect phenotypic differences between H63T and its nearest neighbours using long-established methods, it can be difficult to distinguish Legionella species based on the biochemical tests that are typically done, because various species give similar reactions in many of the tests. For example, L. lansingensis cannot be distinguished from Legionella micdadei and Legionella maceachernii based on standard biochemical profiling (Hookey et al., 1996; Thacker et al., 1992). For this reason, we examined 10 additional characteristics that we have recently found to be expressed variably within the genus Legionella (Söderberg et al., 2008; Starkenburg et al., 2004; Stewart et al., 2009). To that end, cell-free supernatants from late-exponential BYE broth cultures were analysed for protease, acid phosphatase and lipase activities as measured by azocasein, p-nitrophenyl phosphate and p-nitrophenyl palmitate hydrolysis, respectively (Aragon et al., 2000, 2001; Thorpe & Miller, 1981). Strain H63T was positive for both protease and phosphatase activities but lacked lipase activity, a finding that distinguished it from all nine of its nearest neighbours (Table 2). That H63T had these activities in BYE culture supernatants suggests that the strain has a functional type-II protein secretion system, as has been documented extensively in L. pneumophila (Cianciotto, 2009; Pearce & Cianciotto, 2009). Interestingly, in L. pneumophila, a functional type-II secretion system has also been linked to sliding on low-agar media (Stewart et al., 2009) and growth at low temperature (Söderberg et al., 2008). H63T exhibited swimming motility by wet-mount microscopy of 3-day-old BCYE agar-grown cultures, but did not show sliding motility (surface translocation) and its associated surfactant when grown on 0.5 % agar BCYE plates incubated at 30 °C for 14 days (Stewart et al., 2009). These data indicated further differences between H63T and L. brunensis, L. londiniensis, L. feeleii and L. pneumophila (Table 2). Strain H63T was unable to grow at 17 °C on BCYE agar, differentiating it from eight of its nine nearest neighbours; L. londiniensis was the only other species in the panel that did not grow under this low-temperature condition (Table 2). That H63T did not exhibit sliding motility nor grow at 17 °C on BCYE agar would suggest that it lacks those type-II-dependent factors associated with sliding and low-temperature growth. Unlike L. brunensis, L. erythra, L. dresdenensis, L. rubrilucens, L. feeleii, L. pneumophila and L. birminghamensis, H63T grew very poorly at 37 °C on BCYE agar depleted for iron by the addition of 14 µM deferoxamine mesylate (Table 2) (Chatfield et al., 2011). This result suggested that the strain has a higher-than-average iron requirement and/or a reduced ability to scavenge iron. In support of this hypothesis, H63T, un
การกำหนดความสัมพันธ์ระหว่าง H63T และพันธุ์อื่น ๆ Legionella เพิ่มเติม ส่วน bp 584 ของยีน mip และส่วน bp 327 ของยีน rnpB ของ H63T ถูกเรียงลำดับตามที่อธิบายไว้ก่อนหน้านี้ (Kuroki et al., 2007 Lück et al., 2010 Ratcliff และ al., 1998 Rubin et al., 2005 ยาง et al., 2012) กลุ่มทำงานที่ยุโรปสำหรับฐานข้อมูลลำดับยีน mip Legionella เชื้อ Legionella (EWGLI) ถูกใช้เพื่อกำหนดเฉพาะตาม mip และระเบิด NCBI ถูกใช้เพื่อระบุความคล้ายคลึงกันตาม rnpB (Altschul และ al., 1990 ทอด et al., 2007) เช่นเดียวกับยีน 16S rRNA ลำดับการวิเคราะห์ ลำดับยีน mip ของต้องใช้ H63T สุดของ L. brunensis ATCC 43878T (85.49%), ตาม ด้วย hackeliae Legionella ATCC 35250T (85.11%), L. jamestowniensis ATCC 35298T (85.11%), L. feeleii ATCC 35072T (83.95%) และ L. lansingensis ATCC 49751T (83.56%) ใช้ในการวิเคราะห์ลำดับ rnpB ต้องใช้ H63T ได้อีกที่สุดคล้ายกับชนิดสายพันธุ์ของ brunensis L. (91.2%), ตาม ด้วยสายพันธุ์ชนิด L. lansingensis (89.4%), L. jamestowniensis (89.7%), L. hackeliae (88.3%) และ L. feeleii (88.3%) วิเคราะห์ phylogenetic, 16S rRNA, mip และ rnpB ลำดับของสายพันธุ์ชนิดพันธุ์ Legionella และการ อื่น ๆ ญาติภายใน Legionellaceae, Coxiella burnetii ได้รับจาก GenBank (Benson et al., 2008) ลำดับปใด ๆ ได้จัดโดยใช้โปรแกรม CLUSTAL W (Larkin et al., 2007) ต้นไม้ phylogenetic ถูกสรุป โดยวิธีรวมเพื่อนบ้านใช้ TOPALI เวอร์ชัน 2 และแก้ไขใช้ TreeView รุ่น 1.6.6 (Milne et al., 2009 หน้า 1996) วิเคราะห์ phylogenetic ตามตำแหน่งมติของ 16S rRNA, mip และลำดับยีน rnpB ระบุว่า ต้องใช้ H63T เคียงเกี่ยวข้องกับ L. brunensis ตามกลุ่มของ L. hackeliae และ L. jamestowniensis (Fig. 1) ความแข็งแรงของสมาคมที่ได้รับการยืนยัน โดยค่าเริ่มต้นระบบที่เหมือนกับตาม 100 ≥ 80 สำหรับความสมบูรณ์ hybridizations ดีเอ็นเอดีเอ็นเอได้ดำเนินการเปรียบเทียบ H63T กับ hackeliae L. ATCC 35250T และ L. jamestowniensis ATCC 35298T เนื่องจากพวกเขาอย่างใกล้ชิดเกี่ยวข้องตามมติแผนภูมิ ตามการวิเคราะห์ hybridization, L. hackeliae ATCC 35250T ได้ 8.0% (±0.9) ที่เกี่ยวข้องกับ H63T เมื่อ H63T ดีเอ็นเอทำหน้าที่เป็นตัวโพรบและ 31.7% (±0.4) คล้ายเมื่อ H63T แสดง covalent DNA L. jamestowniensis ATCC 35298T ได้ 10.1% (±1.2) คล้ายกับ H63T เมื่อ H63T ดีเอ็นเอ โพรบและ 7.7% (±3.3) คล้ายเมื่อ H63T ดีเอ็นเอ covalent DNA โทของแต่ละยีนสนับสนุนการกำหนดมติของ H63T และ L. brunensis เป็นน้องสาว taxa (มะเดื่อ S1 – S3 ในออนไลน์ IJSEM)ดูรุ่นใหญ่:ในหน้าต่างนี้ในหน้าต่างใหม่ดาวน์โหลดเป็นภาพนิ่ง PowerPointFig. 1เพื่อนบ้านเข้าร่วมแผนภูมิแสดงความสัมพันธ์ระหว่างต้องใช้ H63T และทั้งหมดก่อนหน้านี้เรียงลำดับสายพันธุ์ชนิดพันธุ์ Legionella ตามลำดับในมติของการ 16S rRNA, mip และ rnpB loci มีแสดงซึ่งมีค่ามากกว่า 50 (จาก 100 เหมือนกับ) เริ่มต้นระบบ Coxiella burnetii RSA 493 ถูกใช้เป็น outgroup การ หมายเลขทะเบียน GenBank ลำดับแต่ละที่ใช้ในการสร้างแผนภูมิมีในมะเดื่อ S1 – S3 บาร์ 0.1 แทนต่อไซต์นิวคลีโอไทด์การวิเคราะห์ทางพันธุกรรมของเรา เนื้อหาดีเอ็นเอ G + C ของ H63T ที่ถูกกำหนดผ่านดำเนินการ โดยบริการรหัส DSMZ การวิเคราะห์ HPLC เนื้อหาดีเอ็นเอ G + C ของ H63T มีโมล% 41.8 ภายในช่วงของค่าที่รายงานสำหรับใส่ของ (39.0 – 52.0 โมล% ตาราง 1)ใช้ภาพนิ่ง agglutination ทดสอบอธิบายไว้ก่อนหน้านี้ (Thacker และ al., 1985), ตรวจหาจาก H63T ไม่ได้ไม่ตอบสนอง มี antisera ที่สร้างขึ้นก่อนหน้านี้กับสายพันธุ์ชนิดพันธุ์ Legionella รวมจะขึ้นกับทั้งหมดของประเทศเพื่อนบ้านที่ใกล้ที่สุดในต้นยีน 16S rRNA เป็นสายพันธุ์ชนิด L. jamestowniensis และ L. hackeliae (ตาราง S1)เริ่มแรก เรากำหนด phenotype ของต้องใช้ H63T โดยตรวจสอบชุดของลักษณะสรีรวิทยา 13 ที่มาตรฐาน Legionella (ตาราง 2) (Hookey et al., 1996) เช่นสมาชิกส่วนใหญ่ของพืชสกุล Legionella (เดนนิส et al., 1993 Edelstein et al., 2012 Hookey et al., 1996 ยาง et al., 2012), รวมทั้งประเทศเพื่อนบ้านที่ใกล้ที่สุด H63T เติบโตดีที่ 37 ° C agar (BCYE) สารสกัดจากยีสต์ถ่านถูกบัฟเฟอร์ หรือซุปสกัด (ลาก่อน) ยีสต์ถูกบัฟเฟอร์และ cysteine เสริมจำเป็นสำหรับการเจริญเติบโต อาณานิคมต้องใช้ H63T บน BCYE agar ได้ไม่ autofluoresce ภายใต้แสง UV การแยกสายพันธุ์จากของเพื่อน L. erythra, L. dresdenensis, L. rubrilucens และ L. birminghamensis (ตารางที่ 2) สายพันธุ์ เช่นหลายอื่น ๆ legionellae (Hookey et al., 1996) แต่แตกต่าง จาก L. dresdenensis และ L. birminghamensis, secreted รงควัตถุสีน้ำตาลขนาดกับระยะ (ตารางที่ 2) (Chatfield & Cianciotto, 2007) สำหรับหมักน้ำตาลกลูโคส ไนเตรตลด ยู catalase, oxidase และ gelatinase ดำเนินตามที่อธิบายไว้ก่อนหน้านี้ (Orrison และ al., 1983 ช่างทอผ้าและ Feeley, 1979) ได้ใช้แบคทีเรียเขียนระยะจาก BCYE agar มีประเมินกิจกรรมไฮโตรไลซ์β-Lactamase และ hippurate โดยดิสก์ assays (Becton สัน) ตามที่อธิบายไว้ก่อนหน้านี้ (Kuroki et al., 2007) ตามที่คาดไว้ของสมาชิกของสกุล Legionella (เดนนิส et al., 1993 ช่างทอผ้าและ Feeley, 1979 ยาง et al., 2012), H63T ถูกลบสำหรับหมักน้ำตาลกลูโคส ลดไนเตรต และยูกิจกรรม (ตารางที่ 2) อย่างไรก็ตาม พันธุ์เป็นค่าบวกสำหรับ catalase, gelatinase β-lactamase และ hippurate ไฮโตรไลซ์ (ตาราง 2) ไฮโตรไลซ์ hippurate บวกขอทดสอบ H63T แตกต่างจาก L. brunensis, L. londiniensis, L. jordanis, L. erythra, L. dresdenensis, L. rubrilucens และ L. birminghamensis และสถานะของ gelatinase และβ-lactamase differentiated H63T จาก L. feeleii ความจริงที่ว่า H63T มีค่าบวกสำหรับไฮโตรไลซ์ hippurate และสูญค่าบวกสำหรับ oxidase แตกต่างจาก L. hackeliae L. jamestowniensis สองอื่น ๆ สายพันธุ์ที่พบความคล้ายคลึงกันสูงถึง H63T ขึ้นอยู่กับลำดับ mip และ rnpB (Brenner และ al., 1985)ดูตารางนี้:ในหน้าต่างนี้ในหน้าต่างใหม่ตารางที่ 2 ลักษณะแตกต่างของ H63T เมื่อเทียบกับประเทศเพื่อนบ้านที่ใกล้ที่สุดต้องใช้ตาม 16S rRNA ลำดับยีนสายพันธุ์: 1, L. cardiaca sp. nov H63T (ข้อมูลจากการศึกษา); 2, L. brunensis ATCC 43878T (เว้นแต่ระบุ ข้อมูลจาก Wilkinson et al., 1988); 3, L. londiniensis ATCC 49505T (เดนนิส et al., 1993); 4, L. jordanis ATCC 33623T (เชอร์รี่และ al., 1982); 5, L. erythra ATCC 35303T (Brenner และ al., 1985), 6, L. dresdenensis DSM 19488T (Lück et al., 2010); 7, L. rubrilucens ATCC 35304T (Brenner และ al., 1985); 8, L. feeleii ATCC 35072T (Brenner และ al., 1985); 9, L. pneumophila ATCC 33152T (Brenner et al., 1979); 10, L. birminghamensis ATCC 43702T (Wilkinson et al., 1987) มีทำปฏิกิริยาดังนี้เว้นแต่จะระบุ: +, บวก + W บวกสูญ − ลบ ±, ตัวแปร ND ไม่มีข้อมูล ทุกสายพันธุ์เติบโตบน BCYE ที่ 37 ° C แต่ไม่ได้เติบโตภายใต้เงื่อนไขเหล่านี้ไม่มี cysteine และทุกสายพันธุ์เจริญเติบโตในลาก่อนที่ 37 องศาเซลเซียส สายพันธุ์ทั้งหมดมีค่าเป็นบวกสำหรับ catalase และจะเป็นค่าลบสำหรับหมักน้ำตาลกลูโคส ลดไนเตรต และกิจกรรมยูAlthough we were able to detect phenotypic differences between H63T and its nearest neighbours using long-established methods, it can be difficult to distinguish Legionella species based on the biochemical tests that are typically done, because various species give similar reactions in many of the tests. For example, L. lansingensis cannot be distinguished from Legionella micdadei and Legionella maceachernii based on standard biochemical profiling (Hookey et al., 1996; Thacker et al., 1992). For this reason, we examined 10 additional characteristics that we have recently found to be expressed variably within the genus Legionella (Söderberg et al., 2008; Starkenburg et al., 2004; Stewart et al., 2009). To that end, cell-free supernatants from late-exponential BYE broth cultures were analysed for protease, acid phosphatase and lipase activities as measured by azocasein, p-nitrophenyl phosphate and p-nitrophenyl palmitate hydrolysis, respectively (Aragon et al., 2000, 2001; Thorpe & Miller, 1981). Strain H63T was positive for both protease and phosphatase activities but lacked lipase activity, a finding that distinguished it from all nine of its nearest neighbours (Table 2). That H63T had these activities in BYE culture supernatants suggests that the strain has a functional type-II protein secretion system, as has been documented extensively in L. pneumophila (Cianciotto, 2009; Pearce & Cianciotto, 2009). Interestingly, in L. pneumophila, a functional type-II secretion system has also been linked to sliding on low-agar media (Stewart et al., 2009) and growth at low temperature (Söderberg et al., 2008). H63T exhibited swimming motility by wet-mount microscopy of 3-day-old BCYE agar-grown cultures, but did not show sliding motility (surface translocation) and its associated surfactant when grown on 0.5 % agar BCYE plates incubated at 30 °C for 14 days (Stewart et al., 2009). These data indicated further differences between H63T and L. brunensis, L. londiniensis, L. feeleii and L. pneumophila (Table 2). Strain H63T was unable to grow at 17 °C on BCYE agar, differentiating it from eight of its nine nearest neighbours; L. londiniensis was the only other species in the panel that did not grow under this low-temperature condition (Table 2). That H63T did not exhibit sliding motility nor grow at 17 °C on BCYE agar would suggest that it lacks those type-II-dependent factors associated with sliding and low-temperature growth. Unlike L. brunensis, L. erythra, L. dresdenensis, L. rubrilucens, L. feeleii, L. pneumophila and L. birminghamensis, H63T grew very poorly at 37 °C on BCYE agar depleted for iron by the addition of 14 µM deferoxamine mesylate (Table 2) (Chatfield et al., 2011). This result suggested that the strain has a higher-than-average iron requirement and/or a reduced ability to scavenge iron. In support of this hypothesis, H63T, un
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To define the relationship between H63T and other Legionella species further, a 584 bp portion of the mip gene and a 327 bp portion of the rnpB gene of H63T were sequenced as described previously (Kuroki et al., 2007; Lück et al., 2010; Ratcliff et al., 1998; Rubin et al., 2005; Yang et al., 2012). The European Working Group for Legionella Infections (EWGLI) Legionella mip gene sequence database was used to determine the similarity based on mip, and NCBI BLAST was used to determine similarity based on rnpB (Altschul et al., 1990; Fry et al., 2007). Similar to the 16S rRNA gene sequence analysis, the mip gene sequence of strain H63T was most similar to that of L. brunensis ATCC 43878T (85.49 %), followed by Legionella hackeliae ATCC 35250T (85.11 %), L. jamestowniensis ATCC 35298T (85.11 %), L. feeleii ATCC 35072T (83.95 %) and L. lansingensis ATCC 49751T (83.56 %). Based on analysis of rnpB sequences, strain H63T was again most similar to the type strain of L. brunensis (91.2 %), followed by the type strains of L. lansingensis (89.4 %), L. jamestowniensis (89.7 %), L. hackeliae (88.3 %) and L. feeleii (88.3 %). For phylogenetic analyses, the 16S rRNA, mip and rnpB sequences of type strains of Legionella species and the nearest other relative within the Legionellaceae, Coxiella burnetii, were obtained from GenBank (Benson et al., 2008). Trimmed sequences were aligned using the CLUSTAL W program (Larkin et al., 2007). Phylogenetic trees were inferred by the neighbour-joining method using TOPALI version 2 and edited using TreeView version 1.6.6 (Milne et al., 2009; Page, 1996). Phylogenetic analysis based on the consensus alignment of 16S rRNA, mip and rnpB gene sequences indicated that strain H63T is most closely related to L. brunensis, followed by the group of L. hackeliae and L. jamestowniensis (Fig. 1). The strength of the association was confirmed by bootstrap values ≥80 based on 100 replicates. For completeness, DNA–DNA hybridizations were performed comparing H63T with both L. hackeliae ATCC 35250T and L. jamestowniensis ATCC 35298T, because they were closely related according to the consensus tree. According to hybridization analysis, L. hackeliae ATCC 35250T was 8.0 % (±0.9) related to H63T when H63T DNA served as the probe and 31.7 % (±0.4) similar when H63T represented the covalent DNA. L. jamestowniensis ATCC 35298T was 10.1 % (±1.2) similar to H63T when H63T DNA was the probe and 7.7 % (±3.3) similar when H63T DNA was the covalent DNA. The topologies of the individual gene trees support the consensus assignment of H63T and L. brunensis as sister taxa (Figs S1–S3, available in IJSEM Online).
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Fig. 1.
Neighbour-joining tree showing relationships between strain H63T and all previously sequenced type strains of Legionella species based on the consensus sequence of the 16S rRNA, mip and rnpB loci. Bootstrap values greater than 50 (from 100 replicates) are shown. Coxiella burnetii RSA 493 was used as an outgroup. GenBank accession numbers of the individual sequences used to reconstruct the tree are provided in Figs S1–S3. Bar, 0.1 substitutions per nucleotide site.
To complete our genetic analysis, the DNA G+C content of H63T was determined through HPLC analysis performed by the Identification Service of the DSMZ. The DNA G+C content of H63T was 41.8 mol%, within the range of values reported for its neighbours (39.0–52.0 mol%; Table 1).
Using the slide agglutination test as described previously (Thacker et al., 1985), antigen from H63T did not react with antisera generated previously against the type strains of Legionella species, including sera raised against all of the nearest neighbours in the 16S rRNA gene tree as well as the type strains of L. jamestowniensis and L. hackeliae (Table S1).
Initially, we determined the phenotype of strain H63T by examining a set of 13 physiological traits that are standards for Legionella (Table 2) (Hookey et al., 1996). Like most members of the genus Legionella (Dennis et al., 1993; Edelstein et al., 2012; Hookey et al., 1996; Yang et al., 2012), including its nearest neighbours, H63T grew well at 37 °C on buffered charcoal yeast extract (BCYE) agar or in buffered yeast extract (BYE) broth and required supplementary cysteine for growth. Colonies of strain H63T on BCYE agar did not autofluoresce under UV light, distinguishing the strain from its neighbours L. erythra, L. dresdenensis, L. rubrilucens and L. birminghamensis (Table 2). The strain, like many other legionellae (Hookey et al., 1996) but unlike L. dresdenensis and L. birminghamensis, secreted a brown pigment upon entering stationary phase (Table 2) (Chatfield & Cianciotto, 2007). Tests for glucose fermentation, nitrate reduction, urease, catalase, gelatinase and oxidase were performed as described previously (Orrison et al., 1983; Weaver & Feeley, 1979) using stationary-phase bacteria obtained from BCYE agar. β-Lactamase and hippurate hydrolysis activities were assessed by disc assays (Becton Dickinson) as described previously (Kuroki et al., 2007). As expected of a member of the genus Legionella (Dennis et al., 1993; Weaver & Feeley, 1979; Yang et al., 2012), H63T was negative for glucose fermentation, nitrate reduction and urease activity (Table 2). However, the strain was positive for catalase, gelatinase, β-lactamase and hippurate hydrolysis (Table 2). The strongly positive hippurate hydrolysis test distinguished H63T from L. brunensis, L. londiniensis, L. jordanis, L. erythra, L. dresdenensis, L. rubrilucens and L. birminghamensis, and the presence of both gelatinase and β-lactamase differentiated H63T from L. feeleii. The fact that H63T was positive for hippurate hydrolysis and weakly positive for oxidase distinguishes it from L. hackeliae and L. jamestowniensis, the two other species that showed high similarity to H63T based on mip and rnpB sequences (Brenner et al., 1985).
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Table 2. Differential characteristics of strain H63T compared with its nearest neighbours based on 16S rRNA gene sequences
Strains: 1, L. cardiaca sp. nov. H63T (data from this study); 2, L. brunensis ATCC 43878T (unless indicated, data from Wilkinson et al., 1988); 3, L. londiniensis ATCC 49505T (Dennis et al., 1993); 4, L. jordanis ATCC 33623T (Cherry et al., 1982); 5, L. erythra ATCC 35303T (Brenner et al., 1985), 6, L. dresdenensis DSM 19488T (Lück et al., 2010); 7, L. rubrilucens ATCC 35304T (Brenner et al., 1985); 8, L. feeleii ATCC 35072T (Brenner et al., 1985); 9, L. pneumophila ATCC 33152T (Brenner et al., 1979); 10, L. birminghamensis ATCC 43702T (Wilkinson et al., 1987). Reactions are scored as follows unless indicated: +, positive; +W, weakly positive; −, negative; ±, variable; ND, no data available. All strains grow on BCYE at 37 °C but do not grow under these conditions without cysteine, and all strains grow in BYE at 37 °C. All strains are positive for catalase and are negative for glucose fermentation, nitrate reduction and urease activity.
Although we were able to detect phenotypic differences between H63T and its nearest neighbours using long-established methods, it can be difficult to distinguish Legionella species based on the biochemical tests that are typically done, because various species give similar reactions in many of the tests. For example, L. lansingensis cannot be distinguished from Legionella micdadei and Legionella maceachernii based on standard biochemical profiling (Hookey et al., 1996; Thacker et al., 1992). For this reason, we examined 10 additional characteristics that we have recently found to be expressed variably within the genus Legionella (Söderberg et al., 2008; Starkenburg et al., 2004; Stewart et al., 2009). To that end, cell-free supernatants from late-exponential BYE broth cultures were analysed for protease, acid phosphatase and lipase activities as measured by azocasein, p-nitrophenyl phosphate and p-nitrophenyl palmitate hydrolysis, respectively (Aragon et al., 2000, 2001; Thorpe & Miller, 1981). Strain H63T was positive for both protease and phosphatase activities but lacked lipase activity, a finding that distinguished it from all nine of its nearest neighbours (Table 2). That H63T had these activities in BYE culture supernatants suggests that the strain has a functional type-II protein secretion system, as has been documented extensively in L. pneumophila (Cianciotto, 2009; Pearce & Cianciotto, 2009). Interestingly, in L. pneumophila, a functional type-II secretion system has also been linked to sliding on low-agar media (Stewart et al., 2009) and growth at low temperature (Söderberg et al., 2008). H63T exhibited swimming motility by wet-mount microscopy of 3-day-old BCYE agar-grown cultures, but did not show sliding motility (surface translocation) and its associated surfactant when grown on 0.5 % agar BCYE plates incubated at 30 °C for 14 days (Stewart et al., 2009). These data indicated further differences between H63T and L. brunensis, L. londiniensis, L. feeleii and L. pneumophila (Table 2). Strain H63T was unable to grow at 17 °C on BCYE agar, differentiating it from eight of its nine nearest neighbours; L. londiniensis was the only other species in the panel that did not grow under this low-temperature condition (Table 2). That H63T did not exhibit sliding motility nor grow at 17 °C on BCYE agar would suggest that it lacks those type-II-dependent factors associated with sliding and low-temperature growth. Unlike L. brunensis, L. erythra, L. dresdenensis, L. rubrilucens, L. feeleii, L. pneumophila and L. birminghamensis, H63T grew very poorly at 37 °C on BCYE agar depleted for iron by the addition of 14 µM deferoxamine mesylate (Table 2) (Chatfield et al., 2011). This result suggested that the strain has a higher-than-average iron requirement and/or a reduced ability to scavenge iron. In support of this hypothesis, H63T, un
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