A limited role for beta-selection during gamma delta T cell development.

T cells belong to two distinct lineages expressing either alpha beta or gamma delta TCR. During alpha beta T cell development, it is clearly established that productive rearrangement at the TCR beta locus in immature precursor cells leads to the expression of a pre-TCR complex. Signaling through the pre-TCR results in the selective proliferation and maturation of TCR beta+ cells, a process that is known as beta-selection. However, the potential role of beta-selection during gamma delta T cell development is controversial. Whereas PCR-RFLP and sequencing techniques have provided evidence for a bias toward in-frame VDJ beta rearrangements in gamma delta cells (consistent with beta-selection), gamma delta cells apparently develop normally in mice that are unable to assemble a pre-TCR complex due to a deficiency in TCR beta or pT alpha genes. In this report, we have directly addressed the physiologic significance of beta-selection during gamma delta cell development in normal mice by quantitating intracellular TCR beta protein in gamma delta cells and correlating its presence with cell cycle status. Our results indicate that beta-selection plays a significant (although limited) role in gamma delta cell development by selectively amplifying a minor subset of gamma delta precursor cells with productively rearranged TCR beta genes.

Uma análise de CP não expandido para o sistema de complementadores do Crioulo de Cabo Verde

A temática deste artigo recai sobre a chamada periferia esquerda da frase em crioulo de Cabo Verde (variante de Santiago – CCV), especificamente sobre o seu sistema de complementadores. À semelhança de outras línguas, o CCV exibe construções sintácticas que exigem a projecção do CP, cuja função é identificar/cunhar uma frase, na perspectiva da Hipótese de Cunhagem das Frases, de Cheng (1991). Concretamente, Cheng propõe que as línguas podem ser classificadas relativamente à forma como a cunhagem opera, i.e., através de Mover (e.g., inglês) ou de Merge (e.g., mandarim). Note-se, contudo, que algumas línguas exibem uma tipologia mista, como o árabe egípcio e o bahasa indonésio. Neste artigo, pretende-se (i) apresentar uma descrição dos elementos que podem ocorrer em Cº em CCV e (ii) propor uma análise baseada em traços formais que dê conta da distribuição dos complementadores do CCV, sem precisar de recorrer à hipótese do CP expandido, de Rizzi (1997).

WH-Constructions in Cape Verdean Creole

This dissertation concerns two types of wh-constructions – interrogative and relative clauses – of Cape Verdean Creole (CVC), a Portuguese-based Creole language spoken on the archipelago of Cape Verde, specifically the variety spoken on Santiago Island, in the coast of West Africa. Chapter 2 focus on some aspects of the syntax of CVC, claiming that the possibilities of S-V inversion are very limited and that verbs stay in Vº, except for the Present tense form of the copula verb e ‘to be’, which is the spell out of the formal feature [Present] of T. It is proposed that CVC exhibits a clause functional structure that is similar to English: [CP [TP [NegP [AspP [VP … ]]]]]. In this chapter, it is also suggested that a non Split-CP, based on the formal features [±D, ±V, ±Q, ±Wh, ±T], correctly accounts for the distribution of the complementizers in CVC. Chapter 3 presents the wh-question formation strategies exhibited by CVC, showing that some of them involve Move, while others do not. Considering CVC data, it is said that the language has two clausal typing processes: an ambiguous complementizer ki ([±Q, ±Wh]), whose checking domain is strictly local; and an unambiguous complementizer Ø ([+Q, +Wh]), whose checking domain is not strictly local. The first one derives fronted wh-questions and the second one accounts for wh-in- -situ. Chapter 4 describes the relativization strategies displayed by CVC, focusing on the fact that PP pied-piping is ruled out and that resumption is possible both inside and outside syntactic islands. It is suggested a revision of Bianchi’s (2002a) head raising analysis for the structure of relative clauses. Chapter 5 discusses the properties of the defective copy strategy ([wh[+PL] … el]) and presents evidence in favor of a distinction between this type of wh-strategy and resumption ([wh[+PL] … es]). It is argued that the language requires an overt pronominal form (3SG) to occur in the complement position of the preposition because CVC types the clause with a complementizer ki [uCat +D] and does not allow for preposition incorporation. The set of formal features of the lower copy is ‘shrinked’, i.e. the features are deleted but not erased, being accessible to PF. This analysis of the defective copy xiv strategy predicts that it only applies to PPs and that it is an autonomous process involving wh-movement, which is distinct from resumption.

Linkage arrangement in the vitellogenin gene family of Xenopus laevis as revealed by gene segregation analysis.

Using restriction fragment length polymorphism (RFLP) we have analyzed the segregation of alleles of the different vitellogenin genes of Xenopus laevis. The results demonstrate that the four genes whose expression is controlled by oestrogen, form two linkage groups. The genes A1, A2 and B1 are linked genetically whereas the fourth gene, the gene B2, segregates independently. The possible origin of this unexpected arrangement is discussed.

ESPÉCIES DO GÉNERO CURVULARIA (FUNGOS ANAMÓRFICOS: HYPHOMYCETES) NA ILHA DE SANTIAGO, CABO VERDE

Nos estudos sobre a micoflora de muitos ecossistemas os fungos do género Curvularia Boedijn 1933, constituem um dos mais fascinantes grupos, devido à frequência com que são observados especímenes do género e ao elevado número de espécies que são normalmente identificadas. Apesar da maioria dos táxones do género ser conhecida como saprófita em diferentes substratos vegetais e no solo, podendo ainda ser isolada a partir do solo e do ar, muitas espécies são fitopatogénicas, sobretudo em gramíneas e em regiões de clima tropical e subtropical (SIVANESAN 1987). Um pequeno número de espécies pode raramente originar doenças em animais, incluindo humanos, surgindo como agentes de onicomicoses, sinusite alérgica, pneumonia, endocardite e alergia broncopulmonar (CARTER & BOUDREAUX 2004). Descrito com a espécie tipo C. lunata (Wakker) Boedijn, o género Curvularia permitiu acomodar espécies da família Dematiaceae que possuíam conidióforos macronematosos, mononematosos, direitos ou flexuosos, frequentemente geniculados, por vezes nodosos, células conidiogénicas politétricas, integradas, terminais e simpodiais, fragmoconídios solitários, acropleurógenos por proliferação subterminal do conidióforo, oliváceos a castanhos, elipsóides, cilíndricos, obovóides ou piriformes, três ou mais septos transversais, terceira célula ou segunda e terceira distintamente maiores e escuras, muitas vezes desigualmente curvos devido ao alargamento de uma ou duas células centrais, raramente direitos, septos rígidos, hilo truncado ou protuberante (ELLIS 1971). O género actualmente é composto por mais de 40 táxones que se distinguem por diferenças mais ou menos evidentes na morfologia dos conídios, número de septos e aspectos culturais (SIVANESAN 1987, HOSOKAWA et al. 2003, SIVANESAN et al. 2003, ZHANG-MENG & ZHANG 2003, ZHANG-MENG et al. 2004, CHUNG 2005). Algumas espécies possuem teleomorfo conhecido no género Cochliobolus Drechsler 1934, formando ascósporos filiformes paralelos ou frouxamente enrolados em espiral, característica não evidenciada pela espécie tipo do género, C. heterostrophus (Drechsler) Drechsler, teleomorfo de Bipolaris maydis (Nisik. & Miyake) Shoem., na qual os ascósporos se mostram enrolados formando uma espiral fechada. Por isso, teleomorfos dos fungos do género Curvularia são considerados por alguns autores como sendo do género Pseudocochliobolus Tsuda, Ueyama & Nishih. 1978, que é tido como uma sinonímia de Cochliobolus (ALCORN 1983, SIVANESAN 1987). De notar, no entanto, que sendo filogeneticamente próximo do género Bipolaris Shoem. 1959, as suas espécies apresentam semelhanças morfológicas com espécies do género Bipolaris que têm conídios pequenos e direitos e estudos com análise de sequências ITS e com o marcador enzimático gliceraldeído-3-P desidrogenase mostraram que partilham teleomorfo no grupo 2 do género Cochliobolus (BERBEE et al. 1999). A variabilidade morfológica observada nos fungos enquadrados em Curvularia levou a que ao ser criado o género as espécies fossem separadas em três grupos, ‘geniculata’, com a espécie-tipo C. geniculata (Tracy & Earle) Boedijn, ‘lunata’, com a espécie-tipo C. lunata (Tracy & Earle) Boedijn, e ‘maculans’, com a espécie-tipo C. maculans (Bancroft) Boedijn (=C. eragrostidis (Henn.) Mey.), que se diferenciaram pela forma dos conídios e número de septos (CORBETTA 1964). Nos grupos ‘lunata’ e ‘maculans’ ficaram colocadas as espécies com conídios 3-septados e no grupo ‘geniculata’ as espécies que tinham conídios 4- septados ou com maior número de septos. As espécies do grupo ‘lunata’ distinguiram-se das do grupo ‘maculans’ principalmente por apresentarem curvatura mais pronunciada, célula mediana mais volumosa e habitual presença de estroma em cultura. O reconhecimento das características principais do género Curvularia é relativamente fácil, o que permite que seja normalmente possível a identificação ao género de um qualquer espécimen. No entanto, a identificação em espécie é por vezes complicada pelas descrições vagas e ausência de ilustrações em trabalhos mais antigos, inconstância de características morfológicas e biométricas dos esporos, causada por diferentes condições em que ocorre o crescimento, e sobreposição dos valores das medidas apresentadas por diferentes autores (TSUDA & UEYAMA 1982, HOSOKAWA et al. 2003). Contudo, esta situação não impede que a identificação das espécies continue a ser feita numa aproximação fenotípica, com base em características morfológicas e culturais. Recentemente, as espécies C. fallax Boedijn, C. geniculata (Tracy & Earle) Boedijn e C. senegalensis (Speg.) Subram., do grupo ‘geniculata’, que eram aceites como táxones válidos em monografias clássicas do género (ELLIS 1971, SIVANESAN 1987) mostraram-se interférteis (HOSOKAWA et al. 2003), vindo a ser consideradas, com base em características morfológicas e análise de DNA total por RFLP (HOSOKAWA et al. 2003) e na análise da sequência do gene Brn1 (SUN et al. 2003), como espécie única e sinonimizadas com C. geniculata. Sabido que a diversidade dos fungos que ocorrem nos diferentes ecossistemas de Cabo Verde tem sido pouco estudada, iniciou-se um levantamento da micoflora associada a gramíneas, tendo-se obtido uma colecção de Magnaporthe grisea (Hebert) Barr (LIMA & DUCLOS 2001) e de espécies dos géneros Bipolaris, Exserohilum Leonard & Suggs e Curvularia. O presente trabalho tem como objectivo descrever e ilustrar as espécies de Curvularia identificadas na ilha de Santiago e contribuir para o melhor conhecimento do género naquele país. Na bibliografia consultada não foram encontradas referências a fungos do género Curvularia para Cabo Verde.

The discriminatory power of MALDI-TOF mass spectrometry to differentiate between isogenic teicoplanin-susceptible and teicoplanin-resistant strains of methicillin-resistant Staphylococcus aureus.

To explore the discriminatory power of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for detecting subtle differences in isogenic isolates, we tested isogenic strains of Staphylococcus aureus differing in their expression of resistance to methicillin or teicoplanin. More important changes in MALDI-TOF MS spectra were found with strains differing in methicillin than in teicoplanin resistance. In comparison, very minor or no changes were recorded in pulsed-field gel electrophoresis profiles or peptidoglycan muropeptide digest patterns of these strains, respectively. MALDI-TOF MS might be useful to detect subtle strain-specific differences in ionizable components released from bacterial surfaces and not from their peptidoglycan network.

Molecular characterization of HLA-C incompatibilities in HLA-ABDR-matched unrelated bone marrow donor-recipient pairs. Sequence of two new Cw alleles (Cw*02023 and Cw*0707) and recognition by cytotoxic T lymphocytes.

While the influence of HLA-AB and -DRB1 matching on the outcome of bone marrow transplantation (BMT) with unrelated donors is clear, the evaluation of HLA-C has been hampered by its poor serological definition. Because the low resolution of standard HLA-C typing could explain the significant number of positive cytotoxic T lymphocyte precursor frequency (CTLpf) tests found among HLA-AB-subtype, DRB1/B3/B5-subtype matched patient/donor pairs, we have identified by sequencing the incompatibilities recognized by CD8+ CTL clones obtained from such positive CTLpf tests. In most cases the target molecules were HLA-C antigens that had escaped detection by serology (e.g. Cw*1601, 1502 or 0702). Direct recognition of HLA-C by a CTL clone was demonstrated by lysis of the HLA class I-negative 721.221 cell line transfected with Cw*1601 cDNA. Because of the functional importance of Cw polymorphism, a PCR-SSO oligotyping procedure was set up allowing the resolution of 29 Cw alleles. Oligotyping of a panel of 382 individuals (including 101 patients and their 272 potential unrelated donors, 5 related donors and 4 platelet donors) allowed to determine HLA-C and HLA A-B-Cw-DRB1 allelic frequencies, as well as a number of A-Cw, B-Cw, and DRB1-Cw associations. Two new HLA-Cw alleles (Cw*02023 and Cw*0707) were identified by DNA sequencing of PCR-amplified exon 2-intron 2-exon 3 amplicons. Furthermore, we determined the degree of HLA-C compatibility in 287 matched pairs that could be formed from 73 patients and their 184 potential unrelated donors compatible for HLA-AB by serology and for HLA-DRB1/ B3/B5 by oligotyping. Cw mismatches were identified in 42.1% of these pairs, and AB-subtype oligotyping showed that 30% of these Cw-incompatible pairs were also mismatched for A or B-locus subtype. The degree of HLA-C incompatibility was strongly influenced by the linkage with B alleles and by the ABDR haplotypes. Cw alleles linked with B*4403, B*5101, B18, and B62 haplotypes were frequently mismatched. Apparently high resolution DNA typing for HLA-AB does not result in full matching at locus C. Since HLA-C polymorphism is recognized by alloreactive CTLs, such incompatibilities might be as relevant as AB-subtype mismatches in clinical transplantation.

Ecological temporal stability of Staphylococcus aureus nasal carriage.

We described the colonization dynamics of Staphylococcus aureus in a group of 266 healthy carriers over a period of approximately 1 year. We used precise genotyping methods, i.e., amplified fragment length polymorphism (AFLP), spa typing, and double-locus sequence typing (DLST), to detect changes in strain identity. Strain change took place rather rarely: out of 89 carriers who had initially been colonized, only 7 acquired a strain different from the original one. Approximately one-third of the carriers eliminated the colonization, and a similar number became newly colonized. Some of these events probably represent detection failure rather than genuine colonization loss or acquisition. Lower bacterial counts were associated with increased probability of eliminating the colonization. We have confirmed a high mutation rate in the spa locus: 6 out of 53 strains underwent mutation in the spa locus. There was no overall change in S. aureus genotype composition.

Avaliação da diversidade genética de fungos micorrízicos arbusculares em três estádios de estabilização de dunas

A diversidade genética de fungos micorrízicos arbusculares, recuperados de três estádios de estabilização de dunas, foi avaliada por técnicas moleculares e comparada com resultados obtidos anteriormente por técnicas baseadas na caracterização morfológica dos esporos. O uso da técnica de PCR-RFLP do rDNA, extraído de esporos, permitiu definir impressões características de espécies presentes nas dunas, evidenciar a presença de diferentes comunidades em cada estádio e identificar a anteduna como aquela com comunidades com maior polimorfismo. Esse estádio também apresentou maior diversidade, quando, no estudo das comunidades, foram utilizadas técnicas baseadas em aspectos morfológicos. A combinação de ambas as estratégias, molecular e baseada em aspectos morfológicos, forneceu importantes informações sobre a diversidade destes fungos, visando ao estudo do seu papel no ecossistema.

Teclat virtual amb predicció del llenguatge

L'objectiu de la realització d'aquest treball és la creació d'un teclat virtual destinat a ajudar a persones amb mobilitat reduïda, que no poden utilitzar el teclat físic de l'ordinador, a escriure intentant aconseguir una velocitat d'escriptura raonable per a textos de qualsevol mida. Per aconseguir aquesta velocitat d'escriptura raonable s'ha implementat un sistema de predicció del llenguatge que té dos aspectes. D'una banda es prediuen paraules segons la seva freqüència d'ús en un determinat diccionari i, d'altra banda, es prediuen paraules seguint les regles d'escriptura de la gramàtica catalana. Un altre aspecte important era que el programa creat es pogués utilitzar en diferents sistemes operatius ja que només hi havia versions específiques per a cada un d'ells. El programa creat es pot executar en els sistemes operatius Windows XP, Mac OS i Ubuntu Linux. El programa creat pretén ser una base per a posteriors millores i ampliacions en diferents parts del seu conjunt. No obstant això, com a resultat s'ha obtingut un programa que permet escriure raonablement ràpid i permet a l'usuari gestionar diccionaris i els dos tipus de predicció que s'han implementat.

Invasive mould infections: a multi-disciplinary update.

Systemic fungal infections remain a significant cause of mortality in neutropenic and immunocompromised patients, despite advances in their diagnosis and treatment. The incidence of such infections is rising due to the use of intensive chemotherapy regimens in patients with solid tumours or haematological cancers, the increasing numbers of allogeneic haematopoietic stem cell and solid organ transplants, and the use of potent immunosuppressive therapy in patients with autoimmune disorders. In addition, the epidemiology of systemic fungal infections is changing, with atypical species such as Aspergillus terreus and zygomycetes becoming more common. Treatment has traditionally focused on empirical therapy, but targeted pre-emptive therapy in high-risk patients and prophylactic antifungal treatment are increasingly being adopted. New treatments, including lipid formulations of amphotericin B, second-generation broad-spectrum azoles, and echinocandins, offer effective antifungal activity with improved tolerability compared with older agents; the potential impact of these treatments is reflected in their inclusion in current treatment and prophylaxis guidelines. New treatment strategies, such as aerosolized lipid formulations of amphotericin B, may also reduce the burden of mortality associated with systemic fungal infections. The challenge is to identify ways of coupling potentially effective treatments with early and reliable identification of patients at highest risk of infection.

Staphylococcus aureus clfB and spa alleles of the repeat regions are segregated into major phylogenetic lineages.

To reliably differentiate among Staphylococcus aureus isolates we recently developed the Double Locus Sequence Typing (DLST) based on the analysis of partial sequences of clfB and spa genes. This method is highly discriminatory and gives unambiguous definition of types. The highly clonal population structure of S. aureus suggests that isolates with identical clfB or spa alleles belong to the same clonal complex (CC) defined by Multi-Locus Sequence Typing (MLST). To test this hypothesis as well as to investigate putative intra-CC genetic structure, we analyzed a total of 289 isolates (186 MSSA and 103 MRSA) with DLST-, spa- and MLST-typing. Among the 289 strains, 242 were clustered into 7 major MLST CCs, 40 into minor CCs and 7 were not grouped into CCs. A total of 205 DLST- and 129 spa-types were observed. With one exception, all DLST-clfB, DLST-spa and spa-type alleles were segregated into CCs. DLST-types sharing an identical allele (clfB or spa) were clustered using eBURST. Except for one strain, all isolates from each DLST cluster belonged to the same CC. However, using both DLST- and spa-typing we were not able to disclose a clear intra-CC structure. Nevertheless, the high diversity of these loci confirmed that they are good markers for local epidemiological investigations.

Local acquisition of methicillin-resistance in predominant Staphylococcus aureus clones of western Switzerland.

Objectives: Recent population genetic studies suggest that the Staphylococcal Chromosome Cassettes mec (SCCmec) was acquired at a global scale much more frequently than previously thought. We hypothesized that such acquisitions can also be observed at a local level. In the present study, we aimed at investigating the diversity of SCCmec in a local MRSA population, where the dissemination of four MRSA clones has been observed (JCM 2007, 45: 3729). Methods: All the MRSA isolates (one per patient) recovered in the Vaud canton of Switzerland from January 2005 to December 2008 were analyzed in this study. We used the Double Locus Sequence Typing (DLST) method, based on clfB and spa loci, and the e-BURST algorithm to group the types with one allele in common (i.e. clone). To increase the discriminatory power of the DLST method, a third polymorphic marker (clfA) was further analyzed on a sub-sample of isolates. The SCCmec type of each isolate was determined with the first two PCRs of the Kondo scheme. Results: DLST analysis indicated that 1884/2036 isolates (92.5%) belong to the four predominant clones. A majority of isolates in each clone harboured an identical SCCmec type: 61/64 (95%) isolates to DLST clone 1−1 SCCmec IV, 1282/1323 (97%) to clone 2−2 SCCmec II, 237/288 (82%) to clone 3−3 SCCmec IV, and 192/209 (92%) to clone 4−4 SCCmec I. Unexpectedly, different SCCmec types were present in a single predominant DLST clone: SCCmec V plus one unusual type in 3 isolates of clone 1−1; SCCmec I, IV, V, VI plus two unusual types in 41 isolates of clone 2−2; SCCmec I, II, VI plus three unusual types in 51 isolates of clone 3−3; and SCCmec II, IV, V plus one unusual type in 17 isolates of clone 4−4. Interestingly, adding a third locus generally did not change the classification of incongruent SCCmec types, suggesting that these SCCmec elements have been acquired locally during the dissemination of the clones. Conclusion: Although the SCCmec diversity within clones was relatively low at a local level, a significant proportion of isolates with different SCCmec have been identified in the four major clones. This suggests that the local acquisition of SCCmec elements is not a rare event and illustrates the great capacity of S. aureus to quickly adapt to its environment by acquiring new genetic elements.

Link between genotype and antimicrobial resistance in bovine mastitis-related Staphylococcus aureus strains, determined by comparing Swiss and French isolates from the Rhône Valley.

Staphylococcus aureus is a major bovine mastitis pathogen. Although the reported antimicrobial resistance was generally low, the emergence of new genetic clusters in bovine mastitis requires examination of the link between antimicrobial resistance and genotypes. Here, amplified fragment length polymorphism (AFLP) profiles and standard antimicrobial resistance profiles were determined in order to characterize a total of 343 S. aureus cow mastitis isolates from two geographically close regions of Switzerland and France. AFLP profiles revealed similar population compositions in the two regions, with 4 major clusters (C8, C20, C97, and C151), but the proportions of isolates in each cluster significantly diverged between the two countries (P = 9.2 × 10⁻⁹). Antimicrobial resistance was overall low (< 5% resistance to all therapeutically relevant molecules), with the exception of penicillin resistance, which was detected in 26% of the isolates. Penicillin resistance proportions differed between clusters, with only 1 to 2% of resistance associated with C20 and C151 and up to 70% associated with bovine C97. The prevalence of C20 and C8 was unexpectedly high and requires further investigation into the mechanism of adaptation to the bovine host. The strong association of penicillin resistance with few clusters highlights the fact that the knowledge of local epidemiology is essential for rational choices of antimicrobial treatment in the absence of susceptibility testing. Taken together, these observations argue in favor of more routine scrutiny of antimicrobial resistance and antibiotic-resistant clones in cattle and the farm environment.

Diversidade de bactérias diazotróficas endofíticas associadas a plantas de milho

Bactérias diazotróficas endofíticas são capazes de promover o crescimento do milho por meio da fixação biológica do nitrogênio (FBN) ou pela produção de fitormônios. Neste estudo, objetivou-se caracterizar a diversidade de bactérias diazotróficas endofíticas associadas a plantas de milho em diferentes locais do Rio Grande do Sul, que apresentavam variações de clima e solo. Para isso, foi usado um método baseado na amplificação do gene nifH grupo I, na análise de fragmentos de restrição (PCR-RFLP) e no seqüenciamento dos genes amplificados. Foram calculados os índices de Shannon-Weaver e Equitabilidade para estimar a diversidade dos diazotróficos, bem como a diversidade de nucleotídeos e divergência entre seqüências, para estimar a diversidade genética das comunidades amostradas. Na avaliação da diferenciação entre as comunidades foi utilizado o teste F ST. Foi detectada maior variação entre as comunidades das diferentes regiões do Estado do que dentro das comunidades de cada região avaliada, particularmente entre comunidades provenientes de diferentes tipos de solo, regime pluviométrico e regiões geográficas. O índice de diversidade de Shannon-Weaver indicou diferenças em termos de diversidade de unidades taxonômicas entre as comunidades avaliadas. As comunidades amostradas da região norte do Rio Grande do Sul, que mostrou maior disponibilidade de água e conteúdo de argila, tenderam a apresentar maior diversidade quando comparada às comunidades amostradas na região sul. A análise de Equitabilidade mostrou a dominância de unidades taxonômicas dentro de cada comunidade avaliada, independentemente da região amostrada. Todas as seqüências obtidas foram classificadas como pertencentes ao gene nifH grupo I. Foram obtidas seqüências pertencentes às classes Alfa, Beta e Gama-proteobactéria. Esses resultados demonstraram que existe grande diversidade de bactérias endofíticas fixadoras de N capazes de colonizar o interior de plantas de milho e que as diferentes condições edafoclimáticas estão correlacionadas com a diversidade dos genes nifH.