植物病原细菌Pseudomonas syringae pv. tomato基因组中的信号肽分析

应用SignalP 3.0 对植物病原细菌Pseudomonas syringae pv. tomato DC3000菌株基因组中的全部5 615个ORFs进行了分析,确定其中679个ORFs所编码蛋白质的N-端有信号肽序列,其中已经命名并有注释的有107个ORFs。信号肽的长度以19 ~31 个氨基酸居多,其中最多的是23 个氨基酸的信号肽。具有信号肽的ORFs编码蛋白的长度大多为101~400 个氨基酸之间。同时,对组成信号肽的氨基酸种类作了系统的分析,发现组成信号肽的氨基酸中非极性氨基酸占48.54%,极性氨基酸占18.67%,带负电荷氨基酸占24.54%,带正电荷氨基酸仅占8.00%,出现最多的3种氨基酸依次为亮氨酸、丙氨酸和丝氨酸,最少的氨基酸是异亮氨酸,在切割位点-1端的氨基酸中83.211%均为丙氨酸,在切割位点后3位的氨基酸中最多的氨基酸也是丙氨酸。通过分析确定628个分泌类信号肽,36个信号肽具有RR-motif的保守区段,15个脂蛋白类信号肽,未发现Prepilin-like 信号肽和Bacteriocin and Pheromone信号肽。     

根癌土壤杆菌C58 Cereon中分泌蛋白信号肽分析

利用SignalP3．0、LipoP1．0、TMHMM2．0和TargetP1．014种蛋白分析软件预测了Agrobacterium tumefaciens C58 Cereon菌株全部基因组的4554个ORF编码的蛋白信号肽,共发现203个信号肽,且它们的氨基酸残基相对保守。其中158条具分泌型信号肽,9条具RR-motif型信号肽,28条具信号肽酶Ⅱ型信号肽,8条具细菌素-信息素型信号肽,但只有分泌蛋白AGR-C-1878p和AGR-C-1880p的信号肽氨基酸残基完全相同,表明信号肽是高度变异的。     

秀丽小杆线虫分泌蛋白组的计算机分析

结合计算机技术和生物信息学的方法,采用组合的信号肽分析软件SignalP v3.0、TargetP v1.01、Big-PI Predictor和TMHMM v2.0,预测了秀丽小杆线虫（Caenorthaditis elegans ws123）的全基因组19855个ORF编码蛋白的信号肽,同时系统分析了信号肽的特征。结果表明,在19855个秀丽小杆线虫的蛋白中,有1990条为带有信号肽的分泌型蛋白,其中,1936条为典型的分泌型信号肽（即信号肽酶Ⅰ型信号肽）,53条为信号肽酶Ⅱ型信号肽,1条为信号肽酶Ⅳ型信号肽;在Ⅰ型信号肽中,有41条为RR-motif亚组型信号肽。在1990条信号肽中,有742条没有典型的N-区,其余1248条包含典型的3个区。比较了秀丽小杆线虫与原核生物分泌蛋白信号肽中20种氨基酸残基在信号肽酶切位点的使用情况,表明：在Ⅰ型信号肽酶切位点,其信号肽中使用的氨基酸总体趋势与原核生物基本相似,但秀丽小杆线虫选用的氨基酸种类更多,变化更大;在Ⅱ型信号肽酶切位点,秀丽小杆线虫脂蛋白信号肽中使用的氨基酸的种类与原核生物有很大的不同。通过与真核单细胞生物比较,作为真核多细胞生物的秀丽小杆线虫,其分泌蛋白信号肽所占比例更高、种类更多,可知线虫信号肽的组成具有很高的多态性,表明该物种的分泌蛋白具有多种功能。此外,分析结果显示,脂蛋白信号肽在结构上比分泌型信号肽更为保守。在秀丽小杆线虫分泌蛋白中出现了少数氨基酸组成完全一致的信号肽,采用BLAST 2 SEQUENECES对具有相同信号肽的分泌蛋白进行了序列比对,结果表明具有相同信号肽的分泌蛋白同源性非常高,它们的存在是生物进化过程中基因倍加（duplication）及环境选择的结果,信号肽特征的详细描述必将对这些蛋白功能的研究提供重要的帮助。      

稻瘟病菌含信号肽小蛋白的计算机分析

结合计算机技术和生物信息学的方法,采用组合的信号肽分析软件SignalPv3.0、TargetPv1.1、Big-PIpredictor、TMHMMv2.0和SecretomeP对已公布的1486个稻瘟菌(magnaporthegrisea)小蛋白基因的N-端氨基酸序列进行信号肽分析,同时系统分析了信号肽的类型及结构。分析结果表明,在1486个稻瘟病菌小蛋白中,119个具有N-端信号肽的典型分泌蛋白。其中116个具有分泌型信号肽,1个具RR-motif型信号肽,2个具信号肽酶II型信号肽。在稻瘟病菌基因组中,分泌型小蛋白的序列是高度趋异的,仅出现少数氨基酸组成完全一致的信号肽,为进一步确认具有相同信号肽的分泌蛋白是否具有同源性,分别用BLAST2SEQUENCES对具有相同信号肽的分泌蛋白进行了序列对比。结果表明,具有相同信号肽的分泌蛋白同源性非常高。同时还采用Sublocv1.0对1486个小蛋白的亚细胞位置进行了预测,结果显示小蛋白的可能功能场所包括细胞质、细胞外、线立体和细胞核,功能场所位于细胞核的小蛋白是最多的。     

嗜酸氧化亚铁硫杆菌基因组分泌蛋白的初步分析

利用信号肽预测软件SignalP v3.0、跨膜螺旋结构预测软件TMHMM v2.0和非经典分泌蛋白预测软件SecretomeP对嗜酸氧化亚铁硫杆菌全基因组的3 218个氨基酸序列进行预测分析.结果表明在嗜酸氧化亚铁硫杆菌中有507个蛋白为分泌蛋白,其中分泌型信号肽120个(其中有9个为RR-motif亚组型信号肽),脂蛋白信号肽3个,Prepilin-like信号肽4个,非经典分泌蛋白380个.并对分泌型信号肽的长度分布、氨基酸使用频率和酶切位点的氨基酸使用频率作了统计.得分最高的100个非经典分泌蛋白中,有36个具有功能分类,主要是参与细胞壁、能量代谢及转运和结合的蛋白质.嗜酸氧化亚铁硫杆菌的这507个分泌蛋白所参与的生化过程可能发生在膜外的周质空间或是菌体外的场所,为该物种与矿物相互作用,以及对环境做出响应服务.     

水稻基腐病细菌毒素的遗传特性和产毒相关的分子标记

[目的]水稻基腐病(Erwinia chrysanthemi pv.zeae)是水稻上重要的细菌病害之一,本论文对该病菌的毒素遗传特性和产毒相关的分子标记进行了研究.[方法]通过化学诱变方法,筛选基腐细菌去质粒的突变体Ech7-mu1;应用RAPD技术,筛选产毒素相关的分子标记.[结果]毒素活性测定结果表明,野生菌Ech7和去质粒菌株Ech7-mu1都能产生毒素.从260条随机引物中,筛选出引物K10,该引物能从不产生毒素的突变株Ech7-4中扩增出大小为2139bp的DNA特异片段,但不能扩增野生菌Ech7,将该片段克隆,测序分析,设计特异引物,在突变体Ech7-4中获得了与毒素产生相关的SCAR分子标记(标记符合率为100%).该基因片段有5个ORFs,其中2个ORFs分别编码NADH-黄素还原酶和N-乙酰转移酶,另外2个不完整的ORFs编码的蛋白分别与Pseudomonas aerginosa(ZP00136947)和Yersinia Pestis(ZP01177873)的抗菌素代谢转运蛋白通透酶(DMT)具有66%和46%的同源率.[结论]水稻基腐细菌毒素的生物合成是由染色体基因编码,与质粒无关.不产生毒素的突变菌株基因突变的位点位于SCAR标记DNA的3'末端.     

志贺氏菌属鲍氏(S. boydii)亚群基因组组成与进化分析

利用比较基因组杂交法(comparative genomic hybridization, CGH)对志贺氏菌属鲍氏(S. boydii)亚群共18个血清型代表菌株的基因组结构组成进行比较分析, 结果显示, 该亚群基因组的“共有骨架”包含2552个与非致病性大肠杆菌K12同源的ORFs. 比对K12基因组, 该亚群所有菌株基因组共同缺失ORFs为199个, 主要涉及外膜蛋白编码基因和O-抗原合成相关基因, 而属于亚群特异性的ORFs主要以噬菌体基因和未知功能ORFs为主, 一些参与铁离子代 谢、运输和Ⅱ型分泌系统基因在大多数的鲍氏菌株中存在. 以比较基因组杂交法得到的进化分析显示: 鲍氏亚群18个血清型代表菌株可分为4组, 其中13型与其他菌株有较大的差异. 这种分组结果与某些代谢相关的基因分布情况存在对应关系. 通过对该亚群“共有骨架”、缺失基因和株特异基因, 以及进化分类等方面的分析, 以期探索该亚群基因组的进化规律, 并为志贺氏菌属鲍氏亚群的致病机理、疫苗研制和药物开发等方面的研究提供重要线索.     

痢疾志贺氏菌亚群的比较基因组学研究与进化分析

利用大肠杆菌K12MG1655株全基因组ORFs和痢疾志贺氏菌A1型Sd51197株特异性ORFs探针制备的芯片,研究了痢疾志贺氏菌13个血清型代表株的基因组组成.结果显示,该血清群成员的基因组中包含有2654个保守的源于大肠杆菌ORFs;共同缺失了219个涉及前噬菌体基因、分子伴侣、特异性O抗原合成等大肠杆菌原有的基因;并通过水平转移获得了一些特异性基因,如Ⅱ型分泌系统相关组分、铁转运相关因子等.根据基因组组成所作的进化树,发现A1,A2,A8和A10这四型菌与其他痢疾志贺氏菌亲源关系较远.研究所得结果为进一步深入探索痢疾志贺氏菌的生理过程、致病性和进化奠定了基础.     

茎瘤固氮根瘤菌Azorhizobium caulinodans ORS571基因组分泌蛋白的生物信息学分析

为了获取茎瘤固氮根瘤菌(Azorhizobium caulinodans ORS571)的分泌蛋白,以便更深入地了解该菌的共生固氮作用,本研究采用SignalP、TMHMM、PSORTb、TargetP、LipoP、TatP和SecretomeP软件对该菌全部4717个蛋白序列进行分析预测。结果共识别了653个分泌蛋白,其中具有分泌型信号肽的蛋白54个,具有RR-motif型信号肽的蛋白1个,具有脂蛋白信号肽的蛋白2个和非经典分泌蛋白596个。该菌含信号肽分泌蛋白仅占全部蛋白的1.2%,低于其它固氮菌。在分泌蛋白中识别了核酸内切酶和核糖核酸酶等6个核酸酶。它们可能参与宿主植物遗传物质的降解,干扰宿主遗传代谢,进一步在宿主植物侵染过程中起到重要作用。此外还识别了超氧化物歧化酶、过氧化氢酶和谷胱甘肽S-转移酶等4个抗氧化酶。它们可能参与活性氧的清除以保护固氮酶,是该菌固氮过程的重要参与者。     

痢疾志贺氏菌亚群的比较基因组学研究与进化分析

利用大肠杆菌K12 MG1655株全基因组ORFs和痢疾志贺氏菌A1型Sd51197株特异性ORFs探针制备的芯片, 研究了痢疾志贺氏菌13个血清型代表株的基因组组成. 结果显示, 该血清群成员的基因组中包含有2654个保守的源于大肠杆菌ORFs; 共同缺失了219个涉及前噬菌体基因、分子伴侣、特异性O抗原合成等大肠杆菌原有的基因; 并通过水平转移获得了一些特异性基因, 如Ⅱ型分泌系统相关组分、铁转运相关因子等. 根据基因组组成所作的进化树, 发现A1, A2, A8和A10这四型菌与其他痢疾志贺氏菌亲源关系较远. 研究所得结果为进一步深入探索痢疾志贺氏菌的生理过程、致病性和进化奠定了基础.     

Biosynthesis of a complex yersiniabactin-like natural product via the mic locus in phytopathogen Ralstonia solanacearum

A genome mining study in the plant pathogenic bacterium Ralstonia solanacearum GMI1000 unveiled a polyketide synthase/nonribosomal peptide synthetase gene cluster putatively involved in siderophore biosynthesis. Insertional mutagenesis confirmed the respective locus to be operational under iron-deficient conditions and spurred the isolation of the associated natural product. Bioinformatic analyses of the gene cluster facilitated the structural characterization of this compound, which was subsequently identified as the antimycoplasma agent micacocidin. The metal-chelating properties of micacocidin were evaluated in competition experiments, and the cellular uptake of gallium-micacocidin complexes was demonstrated in R. solanacearum GMI1000, indicating a possible siderophore role. Comparative genomics revealed a conservation of the micacocidin gene cluster in defined, but globally dispersed phylotypes of R. solanacearum.     

Comparative studies of lipopolysaccharide and exopolysaccharide from a virulent strain of Pseudomonas solanacearum and from three avirulent mutants.

The composition of the Pseudomonas solanacearum lipolysaccharide (LPS) was found to be similar to that described for the LPS of enterobacteria. The lipid A contained fatty acids and glucosamine in a molar ratio of 5:2. The LPS fraction contained 2-keto-3-deoxyoctulosonic acid, L-glycero-D-mannoheptose, hexoses (glucose, rhamnose, and glucosamine), and a pentose (xylose). The LPSs from the wild-type strain (GMI1000), from the spontaneous rough mutant (GMI2000), and from their respective acridine orange-resistant (Acrr) mutants (GMI1178 and GMI2179) contained the same component sugars in their polysaccharide moieties, but the relative amounts of each sugar varied greatly. Spontaneous mutation to the rough type was characterized by a decrease in the ratio of rhamnose to glucose, whereas a reverse effect was seen for the acridine orange resistance mutation from the parent strains (GMI1000 and GMI2000) to the respective mutant strains (GMI1178 and GMI2179). The exopolysaccharide (EPS) from GMI1000 was found to be composed of two fractions: a heteropolysaccharide (galactosamine, glucose, and rhamnose) excluded from Sephadex G-50 and an additional glucan with a lower molecular weight. Strains GMI1000 and GMI1178 produced comparable amounts of EPS, GMI2179 synthesized less EPS, and GMI2000 produced no detectable EPS. High-pressure liquid chromatography and 13C nuclear magnetic resonance analyses revealed some differences between these EPSs. The glucan fraction seemed to be the major component of the EPS from GMI2179, whereas GMI1000 and GMI1178 EPSs contained both fractions and appeared to differ in the structures of their heteropolysaccharide fractions. Viscosity measurements confirmed differences between whole EPSs produced by the three strains.     

Natural transformation in the Ralstonia solanacearum species complex: number and size of DNA that can be transferred

Ralstonia solanacearum is a widely distributed phytopathogenic bacterium that is known to invade more than 200 host species, mainly in tropical areas. Reference strain GMI1000 is naturally transformable at in vitro and also in planta conditions and thus has the ability to acquire free exogenous DNA. We tested the ubiquity and variability of natural transformation in the four phylotypes of this species complex using 55 strains isolated from different hosts and geographical regions. Eighty per cent of strains distributed in all the phylotypes were naturally transformable by plasmids and/or genomic DNA. Transformability can be considered as a ubiquitous physiological trait in the R. solanacearum species complex. Transformation performed with two independent DNA donors showed that multiple integration events occurred simultaneously in two distant genomic regions. We also engineered a fourfold-resistant R. solanacearum GMI1000 mutant RS28 to evaluate the size of DNA exchanged during natural transformation. The results demonstrated that this bacterium was able to exchange large DNA fragments ranging from 30 to 90 kb by DNA replacement. The combination of these findings indicated that the natural transformation mechanism could be the main driving force of genetic diversification of the R. solanacearum species complex.     

Induction of lateral root structure formation on petunia roots: A novel effect of GMI1000 Ralstonia solanacearum infection impaired in Hrp mutants

Ralstonia solanacearum is a soilborne plant pathogen that invades its host via roots. As in many gram-negative bacterial plant pathogens, the R. solanacearum Hrp type III secretion system is essential for interactions of the bacterium with plants; however, the related mechanisms involved in disease expression are largely unknown. In this work, we examined the effects of infection by R. solanacearum GMI1000 and Hrp mutants on the root system of petunia plants. Both the wild-type and mutant strains disturbed the petunia root architecture development by inhibiting lateral root elongation and provoking swelling of the root tips. In addition, GMI100 but not the Hrp mutants induced the formation of new root lateral structures (RLS). This ability is shared by other, but not all, R. solanacearum strains tested. Like lateral roots, these new structures arise from divisions of pericycle founder cells which, nevertheless, exhibit an abnormal morphology. These RLS are efficient colonization sites allowing extensive bacterial multiplication. However, they are not required for the bacterial vascular invasion that leads to the systemic spread of the bacterium through the whole plant, indicating that, instead, they might play a role in the rhizosphere-related stages of the R. solanacearum life cycle.     

Pyramiding unmarked deletions in Ralstonia solanacearum shows that secreted proteins in addition to plant cell-wall-degrading enzymes contribute to virulence

Ralstonia solanacearum, like many phytopathogenic bacteria, makes multiple extracellular plant cell-wall-degrading enzymes (CWDE), some of which contribute to its ability to cause wilt disease. CWDE and many other proteins are secreted to the milieu via the highly conserved type II protein secretion system (T2SS). R. solanacearum with a defective T2SS is weakly virulent, but it is not known whether this is due to absence of all the CWDE or the loss of other secreted proteins that contribute to disease. These alternatives were investigated by creating mutants of wild-type strain GMI1000 lacking either the T2SS or up to six CWDE and comparing them for virulence on tomato plants. To create unmarked deletions, genomic regions flanking the target gene were polymerase chain reaction (PCR)-amplified, were fused using splice overlap extension PCR, were cloned into a suicide plasmid harboring the sacB counter-selectable marker, and then, were site-specifically introduced into the genome. Various combinations of five deletions (delta pehA, delta pehB, delta B, PehC, and Pme) was not statistically different from GMI1000, but all the mutants lacking one or both cellulolytic enzymes (Egl or CbhA) wilted plants significantly more slowly than did the wild type. The GMI-6 mutant that lacks all six CWDE was more virulent than the mutant lacking only its two cellulolytic enzymes, and both were significantly more virulent than the T2SS mutant (GMI-D). Very similar results were observed in wounded-petiole inoculation assays, so GMI-6 and GMI-D appear to be less capable of colonizing tomato tissues after invasion. Because the T2SS mutant was much less virulent than the sixfold CWDE mutant, we conclude that other secreted proteins contribute substantially to the ability of R. solanacearum GMI1000 to systemically colonize tomato plants.     

PopF1 and PopF2, two proteins secreted by the type III protein secretion system of Ralstonia solanacearum, are translocators belonging to the HrpF/NopX family

Ralstonia solanacearum GMI1000 is a gram-negative plant pathogen which contains an hrp gene cluster which codes for a type III protein secretion system (TTSS). We identified two novel Hrp-secreted proteins, called PopF1 and PopF2, which display similarity to one another and to putative TTSS translocators, HrpF and NopX, from Xanthomonas spp. and rhizobia, respectively. They also show similarities with TTSS translocators of the YopB family from animal-pathogenic bacteria. Both popF1 and popF2 belong to the HrpB regulon and are required for the interaction with plants, but PopF1 seems to play a more important role in virulence and hypersensitive response (HR) elicitation than PopF2 under our experimental conditions. PopF1 and PopF2 are not necessary for the secretion of effector proteins, but they are required for the translocation of AvrA avirulence protein into tobacco cells. We conclude that PopF1 and PopF2 are type III translocators belonging to the HrpF/NopX family. The hrpF gene of Xanthomonas campestris pv. campestris partially restored HR-inducing ability to popF1 popF2 mutants of R. solanacearum, suggesting that translocators of R. solanacearum and Xanthomonas are functionally conserved. Finally, R. solanacearum strain UW551, which does not belong to the same phylotype as GMI1000, also possesses two putative translocator proteins. However, although one of these proteins is clearly related to PopF1 and PopF2, the other seems to be different and related to NopX proteins, thus showing that translocators might be variable in R. solanacearum.     

Characterization of the interaction between the bacterial wilt pathogen Ralstonia solanacearum and the model legume plant Medicago truncatula

The soilborne pathogen Ralstonia solanacearum is the causal agent of bacterial wilt and attacks more than 200 plant species, including some legumes and the model legume plant Medicago truncatula. We have demonstrated that M. truncatula accessions Jemalong A17 and F83005.5 are susceptible to R. solanacearum and, by screening 28 R. solanacearum strains on the two M. truncatula lines, differential interactions were identified. R. solanacearum GMI1000 infected Jemalong A17 line, and disease symptoms were dependent upon functional hrp genes. An in vitro root inoculation method was employed to demonstrate that R. solanacearum colonized M. truncatula via the xylem and intercellular spaces. R. solanacearum multiplication was restricted by a factor greater than 1 x 10(5) in the resistant line F83005.5 compared with susceptible Jemalong A17. Genetic analysis of recombinant inbred lines from a cross between Jemalong A17 and F83005.5 revealed the presence of major quantitative trait loci for bacterial wilt resistance located on chromosome 5. The results indicate that the root pathosystem for M. truncatula will provide useful traits for molecular analyses of disease and resistance in this model plant species.     

Identification of open reading frames unique to a select agent: Ralstonia solanacearum race 3 biovar 2

An 8x draft genome was obtained and annotated for Ralstonia solanacearum race 3 biovar 2 (R3B2) strain UW551, a United States Department of Agriculture Select Agent isolated from geranium. The draft UW551 genome consisted of 80,169 reads resulting in 582 contigs containing 5,925,491 base pairs, with an average 64.5% GC content. Annotation revealed a predicted 4,454 protein coding open reading frames (ORFs), 43 tRNAs, and 5 rRNAs; 2,793 (or 62%) of the ORFs had a functional assignment. The UW551 genome was compared with the published genome of R. solanacearum race 1 biovar 3 tropical tomato strain GMI1000. The two phylogenetically distinct strains were at least 71% syntenic in gene organization. Most genes encoding known pathogenicity determinants, including predicted type III secreted effectors, appeared to be common to both strains. A total of 402 unique UW551 ORFs were identified, none of which had a best hit or >45% amino acid sequence identity with any R. solanacearum predicted protein; 16 had strong (E < 10(-13)) best hits to ORFs found in other bacterial plant pathogens. Many of the 402 unique genes were clustered, including 5 found in the hrp region and 38 contiguous, potential prophage genes. Conservation of some UW551 unique genes among R3B2 strains was examined by polymerase chain reaction among a group of 58 strains from different races and biovars, resulting in the identification of genes that may be potentially useful for diagnostic detection and identification of R3B2 strains. One 22-kb region that appears to be present in GMI1000 as a result of horizontal gene transfer is absent from UW551 and encodes enzymes that likely are essential for utilization of the three sugar alcohols that distinguish biovars 3 and 4 from biovars 1 and 2.     

Introduction of bacteriophage Mu into Pseudomonas solanacearum and Rhizobium meliloti using the R factor RP4.

Phage Mu-1 and a thermoinducible derivative, Mu-1 cts 62 were inserted into the broad host range R factor RP4. These hybrid plasmids were transferred by conjugation to a phytopathogenic bacterium Pseudomonas solanacearum GMI 1000 and a legume-root nodule bacterium Rhizobium meliloti 2011. The Mu genome is transcribed and tranlated in these new hosts: P. solanacearum (RP4:Mu cts) cultures have a spontaneous production of about 5 X 10(5) plaque-forming units ml-1 which is similar to the frequency of spontaneous Mu production in E. coli; the Mu production of R. meliloti is lower (about 10(2) plaque-forming units ml-1).     

Only one of the five Ralstonia solanacearum long-chain 3-ketoacyl-acyl carrier protein synthase homologues functions in fatty acid synthesis

Ralstonia solanacearum, a major phytopathogenic bacterium, causes a bacterial wilt disease in diverse plants. Although fatty acid analyses of total membranes of R. solanacearum showed that they contain primarily palmitic (C(16:0)), palmitoleic (C(16:1)) and cis-vaccenic (C(18:1)) acids, little is known regarding R. solanacearum fatty acid synthesis. The R. solanacearum GMI1000 genome is unusual in that it contains four genes (fabF1, fabF2, fabF3, and fabF4) annotated as encoding 3-ketoacyl-acyl carrier protein synthase II homologues and one gene (fabB) annotated as encoding 3-ketoacyl-acyl carrier protein synthase I. We have analyzed this puzzling apparent redundancy and found that only one of these genes, fabF1, encoded a long-chain 3-ketoacyl-acyl carrier protein synthase, whereas the other homologues did not play roles in R. solanacearum fatty acid synthesis. Mutant strains lacking fabF1 are nonviable, and thus, FabF1 is essential for R. solanacearum fatty acid biosynthesis. Moreover, R. solanacearum FabF1 has the activities of both 3-ketoacyl-acyl carrier protein synthase II and 3-ketoacyl-acyl carrier protein synthase I.