Feeding rats a high fat/carbohydrate ratio diet reduces jejunal S/I activity ratio and unsialylated galactose on glycosylated chain of S–I complex

AimsWe examined whether decreasing jejunal sucrase/isomaltase (S/I) activity ratio by feeding rats a high fat/carbohydrate ratio diet is regulated by changing glycosylated chains on the S–I complex.Main methodsJejunal activities of sucrase, isomaltase and β-1,4-galactosyltransferase were examined in rats fed a high fat/carbohydrate or a low fat/carbohydrate ratio diet. The amount of galactose and mannose in the glycosylated chain on the S–I complex in rats fed both diets was determined using RCA₁₂₀ and Con A lectins, respectively. The effects of reducing unsialylated galactose from the glycosylated chain on the S–I complex were assessed by determining sucrase activity in purified S–I complex treated with β-galactosidase.Key findings and significanceFeeding rats a high fat/carbohydrate ratio diet reduced jejunal S/I activity ratio in mucosal homogenates and purified fractions. The level of unsialylated galactose in glycosylated chains on the S–I complex was reduced by feeding rats a high fat/carbohydrate ratio diet. The form with reduced levels of unsialylated galactose had lower sucrase activity than that with more unsialylated galactose. The reduction of galactose on the S–I complex by β-galactosidase in vitro reduced sucrase activity. Feeding rats a high fat/carbohydrate ratio diet also reduced jejunal β-1,4-galactosyltransferase activity. Taken together, decreasing the S/I activity ratio by feeding rats a high fat/carbohydrate diet is associated with the reduction of unsialylated galactose on the glycosylated chain of the S–I complex.     

Fine Mapping of the Gene for Carbohydrate-Deficient Glycoprotein Syndrome, Type I (CDG1): Linkage Disequilibrium and Founder Effect in Scandinavian Families

Carbohydrate-deficient glycoprotein syndrome type I (CDG I) is characterized clinically by severe nervous system involvement and biochemically by defects in the carbohydrate residues in a number of serum glycoproteins. The CDG1 gene was recently localized by us to a 13-cM interval in chromosome region 16p13. In this study 44 CDG I families from nine countries were analyzed with available markers in a region ranging from marker D16S495 to D16S497, and haplotype and linkage disequilibrium analyses were performed. One specific haplotype was found to be markedly overrepresented in CDG I patients from a geographically distinct region in Scandinavia, strongly indicating that CDG I families in this region share the same ancestral CDG1 mutation. Furthermore, analysis of the extent of the common haplotype in these families indicates that the CDG1 gene is located in the region defined by markers D16S513–AFMa284wd5–D16S768–D16S406–D16S502. The critical CDG1 region, in strong linkage disequilibrium with markers AFMa284wd5, D16S768, and D16S406, thus constitutes less than 1 Mb of DNA and less than 1 cM in the very distal part of the CDG1 region defined by us previously.     

Mechanism of protein synthesis inhibition during stationary phase in Bacillus stearothermophil US

Summary The appearance of a protein (association factor I) in ribosomes from Bacillus stearothermophilus at stationary phase of growth is described. Association factor I is present on 30S subunits and 30S–50S ribosomal couples, but not on 50S subunits. This protein is responsible for the low levels of polyphenylalanine synthesis shown by stationary phase ribosomes. Association factor I is able to bind to free 30S–50S ribosomal couples but not to polysomes, and exerts its effect by inhibiting the initiation step of protein synthesis. Ribosomes preincubated with association factor I have a decreased ability for polypeptide snythesis directed phage mRNA or poly(U).     

Biochemical methane potential (BMP) test for thickened sludge using anaerobic granular sludge at different inoculum/substrate ratios

The biochemical methane potential (BMP) test for thickened sludge was evaluated at three different inoculum/substrate (I:S) ratios. The cumulative methane yield was 51.4 mL CH₄/g VS_added at an I:S ratio of 1:1, 76.3 mL CH₄/g VS_added at an I:S ratio of 1:3, and 21.9 mL CH₄/g VS_added at an I:S ratio of 1:8. The greatest ultimate methane yield and methane production rate constant were achieved at an I:S ratio of 1:3, whereas the least was obtained at an I:S ratio of 1:8. The maximum methane production rate constant was 0.38/day and the minimum methane production rate constant was 0.0016/day. For the case of a lower I:S ratio, the biomass activity may be affected due to the low substrate concentration. On the other hand, for the case of higher I:S ratios, anaerobic digestion of thickened sludge was inhibited by higher concentrations of volatile fatty acids and lower pH.     

Magnetic interactions in milk xanthine oxidase

The relaxation behavior of the EPR signals of MoV, FAD semiquinone, and the reduced Fe/S I center was measured in the presence and absence of other paramagnetic centers in milk xanthine oxidase. Specific pairs of prosthetic groups were rendered paramagnetic by poising the native enzyme or its desulfo glycol inhibited derivative at appropriate potentials and pH values. Magnetic interactions were found between the following species: Mo--Fe/S I (100-fold increase in microwave power required to saturate the MoV EPR signal at 103 K when Fe/S I is reduced as opposed to oxidized), FAD--Fe/S I and FAD--Fe/S II (70-fold increase in power required to saturate the FADH.EPR signal at 173 K when either Fe/S center is reduced), and Fe/S I--Fe/S II (2.5-fold increase in power to saturate the reduced Fe/S I EPR signal at 20 K when Fe/S II is reduced). The Mo--Fe/S I interaction was also detected as a reduced Fe/S I induced splitting of the MoV EPR spectrum at 30 K. No splittings of the FADH. or Fe/S center spectra were detected. No magnetic interactions were found between FAD and Mo or between Mo and Fe/S II. These results, together with those of Coffman & Buettner [Coffman, R. E., & Buettner, G. R. (1979) J. Phys. Chem. 83, 2392-2400], were used to estimate the following approximate distances between the electron carrying prosthetic groups of milk xamthine oxidase: Mo--Fe/S I, 11 +/- 3 A; Fe/S I-Fe/S II, 15 +/- 4 A; FAD-Fe/S I, 16 +/- 4 A; FAD-Fe/S II, 16 +/- 4 A. A model for the arrangement of these groups within the xanthine oxidase molecule is suggested.     

Purification and restriction endonuclease mapping of soybean 18 S and 25 S ribosomal RNA genes

The restriction endonuclease map of the 25 S and 18 S ribosomal RNA genes of a higher plant is presented. Soybean (Glycine max) rDNA was enriched by preparative buoyant density centrifugation in CsCl-actinomycin D gradients. The buoyant density of the rDNA was determined to be 1.6988 g cm^–3 by analytical centrifugation in CsCl. Saturation hybridization showed that 0.1% of the total DNA contains 25 S and 18 S rRNA coding sequences. This is equivalent to 800 rRNA genes per haploid genome (DNA content: 1.29 pg) or 3200 for the tetraploid genome. Restriction endonuclease mapping was performed with Bam H I, Hind III, Eco R I, and BstI. The repeating unit of the soybean ribosomal DNA has a molecular weight of 5.9·10⁶ or approximately 9,000 kb. The 25 S and 18 S rRNA coding sequences were localized within the restriction map of the repeating unit by specific hybridization with either [¹²⁵I]25 S or [¹²⁵I]18 S rRNA. It was demonstrated that there is no heterogeneity even in the spacer region of the soybean rDNA.     

中国马蓝属(爵床科)新组合和新分类群(英文)

采用广义的马蓝属(Strobilanthes Blume)概念,提出3个新组合:匍匐半插花(S.primulifolia(Nees)Y.F.DengJ.R.I.Wood),直立半插花(S.cumingiana(Forst.)Y.F.DengJ.R.I.Wood)和狭叶马蓝(S.atropurpurea var.stenophylla(C.B.Clarke)Y.F.DengJ.R.I.Wood);描述了8新种:南岭马蓝(Strobilanthes austrosinensis Y.F.DengJ.R.I.Wood)、冯氏马蓝(S.fengiana Y.F.DengJ.R.I.Wood)、陶氏马蓝(S.taoana Y.F.DengJ.R.I.Wood)、启无马蓝(S.wangiana Y.F.DengJ.R.I.Wood)、景东马蓝(S.atroviridis Y.F.DengJ.R.I.Wood)、西畴马蓝(S.rostrata Y.F.DengJ.R.I.Wood)、黄连山马蓝(S.spiciformis Y.F.DengJ.R.I.Wood)和匍匐马蓝(S.procumbens Y.F.DengJ.R.I.Wood)。对南岭马蓝、黄连山马蓝、景东马蓝和匍匐马蓝的花粉形态进行了观察。     

Entre Ríos Seedeater (Sporophila zelichi): a species that never was

ABSTRACT Entre Ríos Seedeaters (Sporophila zelichi), also called Zelich's Seedeaters, White‐collared Seedeaters, and Narosky's Seedeaters, are one of the rarest birds in the Neotropics. However, doubts have been raised about the validity of this species. Therefore, I evaluated the systematic status of Entre Ríos Seedeaters based on analysis of previously unpublished vocal and habitat data. I tested four hypotheses regarding the systematic status of S. zelichi: Good Species Hypothesis (valid species), Hybridization Hypothesis (hybrid S. palustris×S. cinnamomea), Color Morph Hypothesis I (morph of S. cinnamomea), and Color Morph Hypothesis II (morph of S. palustris). The songs and preferred habitat of S. zelichi are indistinguishable from those of Marsh Seedeaters (S. palustris), and the songs of both forms have exhibited similar changes from the early 1990s to 2003–2007. In contrast, the songs and preferred habitat of Chestnut Seedeaters (S. cinnamomea) differ from those of S. zelichi. Therefore, the Good Species Hypothesis is rejected by vocalization and habitat data, the Hybrid Hypothesis is undermined by the absence of shared vocal characters and limited habitat overlap of the proposed parental forms S. cinnamomea/S. palustris, and Color Morph Hypothesis I is rejected by both song and habitat data. However, Color Morph Hypothesis II is supported by both song and habitat data. Thus, I propose that S. zelichi be considered a color morph of S. palustris.     

两种麦蚜取食诱导小麦抗性品种后对后来取食蚜生物学特性的影响

刺吸式昆虫在刺吸作物韧皮部取食后会影响作物的正常生长发育,随着作物抗性及昆虫种类的不同,作物反过来也会对昆虫造成或正或反的影响,然而一种刺吸式昆虫取食后对后来者有什么样的影响目前尚不确定。本研究通过严谨的实验方法,即选定3个不同国家的小麦抗性品种98-10-30、Amigo和Batis,在所有条件严格统一的人工智能控制温室内,通过各处理在同一植株上先后不同的接蚜方式,分别测定了麦二叉蚜Schizaphis graminum (Rondani)和麦长管蚜Sitobion avenae Fab.在前期被蚜虫危害的抗虫品种98-10-30、Amigo和Batis上的发育历期、体重差及相对日均体重增长率(mean relative growth rate MRGR)等生物学参数。结果表明：品种不同,蚜虫在不同处理条件下取食作物时受到的影响也不同,即在品种98-10-30上,通过与前期不接虫的对照及前期接不同麦蚜的相关处理比较,麦长管蚜对后期取食的麦二叉蚜(MRGR=0.0974±0.0071)具有抑制作用,而麦二叉蚜对后期取食的麦长管蚜(MRGR=0.1614±0.0048)却有促进作用;在品种Amigo上,前期麦蚜的危害对麦长管蚜的取食具有促进作用,而在品种Batis上前期危害对麦二叉蚜的取食具有促进作用。同时明确了3个品种对两种蚜虫的抗性状况,即在前期无蚜虫危害时,品种98-10-30和Batis对两种麦蚜的抗性相当;在前期有麦蚜危害时,品种98-10-30对麦二叉蚜的抗性较好,而品种Batis对麦长管蚜的抗性较好;品种Amigo无论在任何处理下均对麦二叉蚜的抗性较好。     

The Role of miR-34a in the Hepatoprotective Effect of Hydrogen Sulfide on Ischemia/Reperfusion Injury in Young and Old Rats

Hydrogen sulfide (H₂S) can protect the liver against ischemia-reperfusion (I/R) injury. However, it is unknown whether H₂S plays a role in the protection of hepatic I/R injury in both young and old patients. This study compared the protective effects of H₂S in a rat model (young and old animals) of I/R injury and the mechanism underlying its effects. Young and old rats were assessed following an injection of NaHS. NaHS alone reduced hepatic I/R injury in the young rats by activating the nuclear erythroid-related factor 2 (Nrf2) signaling pathway, but it had little effect on the old rats. NaHS pretreatment decreased miR-34a expression in the hepatocytes of the young rats with hepatic I/R. Overexpresion of miR-34a decreased Nrf-2 and its downstream target expression, impairing the hepatoprotective effect of H₂S on the young rats. More importantly, downregulation of miR-34a expression increased Nrf-2 and the expression of its downstream targets, enhancing the effect of H₂S on hepatic I/R injury in the old rats. This study reveals the different effects of H₂S on hepatic I/R injury in young and old rats and sheds light on the involvement of H₂S in miR-34a modulation of the Nrf-2 pathway.     

Equilibrium and nonequilibrium competitive inhibitions of antipeptide antibody binding by parent myelin basic protein and 18 related peptide sequences

Equilibrium and nonequilibrium competitive inhibition analyses of a number of antisera to peptide S81 and S82 sequences were carried out through the use of inhibition radioimmunoassays with [¹²⁵I]S81, [¹²⁵I]S82, and [¹²⁵I]S79 and a panel containing 18 related peptides and five myelin basic protein preparations. Two principal determinants were identified, one of them sequential, the other nonsequential. The sequential determinant involved a peptide at or near the C-terminal end of S82 that could be blocked by an interchange of asparagine for glycine at the C terminus. The nonsequential determinant was dominant for a number of rabbit and rat antisera, both anti-S82 and anti-S81, and was shared not only by S81 and S82 but also by S8 and S80, i.e., the family of residues of bovine MBP sequence 69–83. Neither determinant was expressed in any of the myelin basic protein preparations, and the nonsequential determinant was not expressed in peptide sequences smaller than S8.     

Sphingosine 1-phosphate S1P2 and S1P3 receptor-mediated Akt activation protects against in vivo myocardial ischemia-reperfusion injury

Sphingosine 1-phosphate (S1P) is released at sites of tissue injury and effects cellular responses through activation of G protein-coupled receptors. The role of S1P in regulating cardiomyocyte survival following in vivo myocardial ischemia-reperfusion (I/R) injury was examined by using mice in which specific S1P receptor subtypes were deleted. Mice lacking either S1P(2) or S1P(3) receptors and subjected to 1-h coronary occlusion followed by 2 h of reperfusion developed infarcts equivalent to those of wild-type (WT) mice. However, in S1P(2,3) receptor double-knockout mice, infarct size following I/R was increased by >50%. I/R leads to activation of ERK, JNK, and p38 MAP kinases; however, these responses were not diminished in S1P(2,3) receptor knockout compared with WT mice. In contrast, activation of Akt in response to I/R was markedly attenuated in S1P(2,3) receptor knockout mouse hearts. Neither S1P(2) nor S1P(3) receptor deletion alone impaired I/R-induced Akt activation, which suggests redundant signaling through these receptors and is consistent with the finding that deletion of either receptor alone did not increase I/R injury. The involvement of cardiomyocytes in S1P(2) and S1P(3) receptor mediated activation of Akt was tested by using cells from WT and S1P receptor knockout hearts. Akt was activated by S1P, and this was modestly diminished in cardiomyocytes from S1P(2) or S1P(3) receptor knockout mice and completely abolished in the S1P(2,3) receptor double-knockout myocytes. Our data demonstrate that activation of S1P(2) and S1P(3) receptors plays a significant role in protecting cardiomyocytes from I/R damage in vivo and implicate the release of S1P and receptor-mediated Akt activation in this process.     

利用mtCOI PCR-RFLP技术鉴别草地贪夜蛾与其他3种形态相近昆虫

【目的】田间调查发现草地贪夜蛾与甜菜夜蛾、斜纹夜蛾、粘虫常混合发生,传统的形态学鉴定方法不能快速鉴别出该虫,当前亟需快速鉴别该虫的方法。【方法】本研究分析了草地贪夜蛾与甜菜夜蛾、斜纹夜蛾、粘虫mtCOI基因序列的酶切位点,根据目的片段设计上游引物并进行PCR-RFLP验证。【结果】草地贪夜蛾个体在mtCOI片段的556~561 bp处均存在Sbf I内切酶酶切位点,斜纹夜蛾、甜菜夜蛾、粘虫均无Sbf I酶切位点。草地贪夜蛾PCR产物经过Sbf I内切酶酶切,可出现420 bp左右的特征带,斜纹夜蛾、甜菜夜蛾、粘虫种群均不能被Sbf I内切酶酶切。【结论】基于新设计引物扩增的mtCOI片段的PCR-RFLP方法可有效鉴别草地贪夜蛾与其他3个形态相近昆虫,研究结果为草地贪夜蛾的快速鉴别提供了方法。     

A novel P700 redox kinetics probe for rapid,non‐intrusive and whole‐tissue determination of photosystem II functionality,and the stoichiometry of the two photosystems in vivo

We sought a rapid, non‐intrusive, whole‐tissue measure of the functional photosystem II (PS II) content in leaves. Summation of electrons, delivered by a single‐turnover flash to P700⁺ (oxidized PS I primary donor) in continuous background far‐red light, gave a parameter S in absorbance units after taking into account an experimentally determined basal electron flux that affects P700 redox kinetics. S was linearly correlated with the functional PS II content measured by the O₂ yield per single‐turnover repetitive flash in Arabidopsis thaliana expressing an antisense construct to the PsbO (manganese‐stabilizing protein in PS II) proteins of PS II (PsbO mutants). The ratio of S to z_max (total PS I content in absorbance units) was comparable to the PS II/PS I reaction‐center ratio in wild‐type A. thaliana and in control Spinacea oleracea. Both S and S/z_max decreased in photoinhibited spinach leaf discs. The whole‐tissue functional PS II content and the PS II/photosystem I (PS I) ratio can be non‐intrusively monitored by S and S/z_max, respectively, using a quick P700 absorbance protocol compatible with modern P700 instruments.     

Does melanin affect the low LET radiation response of Cloudman S91 mouse melanoma cell lines?

Melanin contains melanin-free radicals and can both absorb and produce additional free radicals and active oxygen species on exposure to various stimuli. Yet its role in the radiation responses of malignant melanoma has been little studied. In this report, three subclones of Cloudman S91 mouse melanoma clone PC1A varying in constitutive melanin content were compared with respect to killing by gamma irradiation. Radiation responses correlated with melanin content. The least melanotic line, S91/amel, was most sensitive and the most melanotic line, S91/I3, was most resistant. Curve fitting using the linear-quadratic model suggests that S91/amel is killed only by single event inactivations; S91/I3, only by double event inactivations; and S91/M1B, with intermediate melanin and radiation response, by both types of inactivations. Split dose experiments confirmed a lack of immediate split dose recovery in S91/amel and its existence in S91/I3. Potentially lethal damage and its repair could be demonstrated in both S91/amel and S91/I3. Double strand break (DSB) induction was evaluated as a function of gamma ray dose in DNA of S91/I3 and S91/amel, as well as in EMT6, a mouse mammary cancer line that lacks tyrosinase and melanin. The rates of induction were proportional to cellular melanization, i.e., the rate of DSB induction was greatest in S91/I3, least in EMT6. Levels of thioredoxin reductase (TR), glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT) were determined in S91/amel and S91/I3. TR was the same in both cell lines, while the other three enzymes were 3- to 4-fold lower in S91/amel.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced removability of odorous sulfur-containing gases by mixed cultures of purified bacteria from peat biofilters

Four bacteria isolated from peat biofilters, Thiobacillus thioparus DW44, Thiobacillus sp. HA43, Xanthomonas sp. DY44 and Hyphomicrobium sp. I55, were selected to enhance the removal ratios of hydrogen sulfide (H₂S), methanethiol (MT) and dimethyl sulfide (DMS) in a mixed gas system. Two bacteria, DW44 and I55, which degrade H₂S, MT, DMS and dimethyl disulfide (DMDS), were mixed with DY44 or HA43 which degrade only H₂S and MT. Although DMS removal was significantly inhibited by the presence of H₂S and MT in a peat biofilter inoculated with the single bacterium, enhanced removability of H₂S, MT and DMS was observed by mixing Hyphomicrobium sp. I55 either with Thiobacillus sp. HA43 or Xanthomonas sp. DY44. The removal rate (g-S-kg-dry peat⁻¹·d⁻¹) by I55 after 8 d was 0.664 in total sulfur load, 0.827 g-S·kg-dry g-S·-kg-dry peat⁻¹·d⁻¹, but the rates by the mixed cultures of I55 plus HA43, and I55 plus DY44 were 0.760 and 0.801, respectively. In particular, DMS removability in mixed gases by a mixed culture of I55 and DY44 was almost equivalent to that by I55 when only DMS was supplied, suggesting that removal of H₂S and MT, which inhibited DMS removal, was preferentially conducted by DY44 and led to improved DMS removability by I55.     

Two distinct voltage-sensing domains control voltage sensitivity and kinetics of current activation in CaV1.1 calcium channels

Alternative splicing of the skeletal muscle Ca_V1.1 voltage-gated calcium channel gives rise to two channel variants with very different gating properties. The currents of both channels activate slowly; however, insertion of exon 29 in the adult splice variant Ca_V1.1a causes an ∼30-mV right shift in the voltage dependence of activation. Existing evidence suggests that the S3–S4 linker in repeat IV (containing exon 29) regulates voltage sensitivity in this voltage-sensing domain (VSD) by modulating interactions between the adjacent transmembrane segments IVS3 and IVS4. However, activation kinetics are thought to be determined by corresponding structures in repeat I. Here, we use patch-clamp analysis of dysgenic (Ca_V1.1 null) myotubes reconstituted with Ca_V1.1 mutants and chimeras to identify the specific roles of these regions in regulating channel gating properties. Using site-directed mutagenesis, we demonstrate that the structure and/or hydrophobicity of the IVS3–S4 linker is critical for regulating voltage sensitivity in the IV VSD, but by itself cannot modulate voltage sensitivity in the I VSD. Swapping sequence domains between the I and the IV VSDs reveals that IVS4 plus the IVS3–S4 linker is sufficient to confer Ca_V1.1a-like voltage dependence to the I VSD and that the IS3–S4 linker plus IS4 is sufficient to transfer Ca_V1.1e-like voltage dependence to the IV VSD. Any mismatch of transmembrane helices S3 and S4 from the I and IV VSDs causes a right shift of voltage sensitivity, indicating that regulation of voltage sensitivity by the IVS3–S4 linker requires specific interaction of IVS4 with its corresponding IVS3 segment. In contrast, slow current kinetics are perturbed by any heterologous sequences inserted into the I VSD and cannot be transferred by moving VSD I sequences to VSD IV. Thus, Ca_V1.1 calcium channels are organized in a modular manner, and control of voltage sensitivity and activation kinetics is accomplished by specific molecular mechanisms within the IV and I VSDs, respectively.     

New and reassessed species of Strobilanthes (Acanthaceae) in the flora of China

Several problems in Strobilanthes Blume (Acanthaceae: Ruelliae) are clarified as a result of collaboration between Chinese and western botanists. Examination of pollen has permitted clear delimitation of four morphologically similar species, Strobilanthes szechuanica (Batalin) J. R. I. Wood & Y. F. Deng, S. labordei H. Lév., S. wakasana Wakasugi & Naruhashi and S. wilsonii J. R. I. Wood & Y. F. Deng, the latter described for the first time in this paper, although first collected more than a hundred years ago. A key is provided to help distinguish these species. The globose, echinulate pollen found in several species from China and Japan and assigned to the genus Championella by Bremekamp is shown by SEM photography to be distinct from other pollen hitherto regarded as the same. Three new species, S. abbreviata Y. F. Deng & J. R. I. Wood, S. lihengiae Y. F. Deng & J. R. I. Wood and S. vallicola Y. F. Deng & J. R. I. Wood are described. S. austinii C. B. Clarke ex W. W. Sm. is lectotypified to show that it is conspecific with S. lamiifolia (Nees) T. Anderson, a species demonstrating trans-Himalayan links. New combinations are made for four species as the authors recognize only a single genus, Strobilanthes within the Strobilanthinae as defined by Bremekamp. S. gongshanensis Tsui and S. aenobarba W. W. Sm. are shown to be only varieties of S. inflata T. Anderson. Illustrations are provided for all new species.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 369–390.     

I-SceI-mediated plasmid deletion and intra-molecular recombination in Spiroplasma citri

S. citri wild-type strain GII3 carries six plasmids (pSci1 to -6) that are thought to encode determinants involved in the transmission of the spiroplasma by its leafhopper vector. In this study we report the use of meganuclease I-SceI for plasmid deletion in S. citri. Plasmids pSci1NT-I and pSci6PT-I, pSci1 and pSci6 derivatives that contain the tetM selection marker and a unique I-SceI recognition site were first introduced into S. citri strains 44 (having no plasmid) and GII3 (carrying pSci1-6), respectively. Due to incompatibility of homologous replication regions, propagation of the S. citri GII3 transformant in selective medium resulted in the replacement of the natural pSci6 by pSci6PT-I. The spiroplasmal transformants were further transformed by an oriC plasmid carrying the I-SceI gene under the control of the spiralin gene promoter. In the S. citri 44 transformant, expression of I-SceI resulted in rapid loss of pSciNT-I showing that expression of I-SceI can be used as a counter-selection tool in spiroplasmas. In the case of the S. citri GII3 transformant carrying pSci6PT-I, expression of I-SceI resulted in the deletion of plasmid fragments comprising the I-SceI site and the tetM marker. Delineating the I-SceI generated deletions proved they had occurred though recombination between homologous sequences. To our knowledge this is the first report of I-SceI mediated intra-molecular recombination in mollicutes.