Academic literature on the topic 'Microbial antagonists'

The cost of losses and control measures attributed to late blight of potatoes caused by Phytophthora infestans, are estimated to exceed $5 billion annually. Breeding for resistance is difficult owing to the tetraploid genotype of potato and current strains of the pathogen have developed resistance to chemical control. Consequently the search for biological control has assumed greater importance. In this investigation an in vivo bioassay was used to select soils antagonistic to late blight of potatoes, caused by Phytophthora infestans. Four out of eight samples demonstrated reproducible antagonism as determined by a reduction in the volume of tuber tissue rotted. A total of 292 bacterial and yeast samples and 20 fungal samples were recovered from suppressive soils using a variety of non-selective and selective media. When these organisms were tested individually against P. infestans in the assay, 15 isolates suppressed tuber rotting by >85% in at least three out of four assays. The antagonists were characterised as Pseudomonas spp. (3 strains), Enterobacter spp. (4 strains), Bacillus spp. (1 strain), Pantoea spp. (2 strains), Citrobacter spp. (1 strain), Buttiauxella spp. (1 strain), Trichosporon spp. (2 strains) and Geotrichum spp. (1 strain) by routine bacteriological tests, fatty acid profiling and partial sequencing of the gene encoding 16S or 18S (where appropriate) ribosomal RNA. Subsequently the possible mechanisms by which the potential biocontrol agents inhibited the disease were examined. Nine isolates showed some evidence of antibiotic production with a Pantoea spp. producing a compound that caused the hyphae of P. infestans to kink and permanently cease growth. Three isolates colonised hyphae of the pathogen and eleven produced siderophores in liquid culture. Hydrogen cyanide, proteolytic, cellulolytic and beta-1,3-glucanase activity was also evident in some species. Significant promotion of axenically grown tomato seedlings, as determined by increased stem and main root elongation, was achieved by ten of the isolates. Three population levels of the isolates were retested for disease inhibition at the end of the investigation. Isolates 3, 7 and 14 exhibited the highest levels of consistent inhibition at the lowest population levels and were therefore tested in combination. This achieved disease suppression that, at an antagonist concentration of 25 cfu/nL, was more consistent than isolate 3 alone and was over 30% greater than either isolate 7 or 14.

As formigas-cortadeiras (Hymenoptera: Formicidae), gêneros Atta e Acromyrmex, são as pragas mais importantes da silvicultura, encontradas exclusivamente nas Américas. Sua importância econômica se deve ao seu hábito alimentar de cortar material vegetal fresco – sendo algumas importantes espécies cultivadas - que serve de substrato para o fungo simbionte mutualista Leucoagaricus gongylophorus (Basidiomycota: Agaricales) o qual é cultivado em câmaras subterrâneas. As fêmeas fecundadas são responsáveis pela fundação de uma nova colônia e sofrem influência direta de microrganismos presentes no solo, assim existem evidências que fêmeas de Atta spp. recém-fecundadas evitam solos férteis, com alta carga microbiana e mesmo as áreas de matas para fundação dos seus ninhos. Os fungos entomopatogênicos e fungos antagonistas de L. gongylophorus, presentes naturalmente no solo, podem ser usados no controle biológico de formigas-cortadeiras. Os objetivos deste trabalho foram avaliar em laboratório o desenvolvendo de colônias jovens de Atta sexdens em contato com solos de área de mata e de área desnuda, realizar a bioprospecção de isolados de fungos antagonistas de L. gongylophorus (Trichoderma spp.), em solos da região de Gurupi - TO, e testar o efeito antagônico desses fungos contra L. gongylophorus. Após 106 dias da revoada, as operárias de A. sexdens das 36 colônias, logo que iniciado o experimento, removeram o solo em todos os tratamentos, e esse comportamento favoreceu a sobrevivência das colônias, apresentando uma taxa de sobrevivência de 91,67% durante as 13 semanas. Verificou-se que, após as colônias terem passado pelo período crítico de fundação, o tipo de solo parece exercer pouca influência na sobrevivência das operárias e das colônias. O solo de área de mata apresenta maior quantidade e diversidade de fungos filamentosos que o solo de área desnuda; A utilização de Tenebrio molitor como isca-viva é eficiente para bioprospecção por fungos entomopatogênicos. Todos os isolados de Trichoderma foram capazes de inibir o crescimento in vitro de L. gongylophorus; Trichoderma spirale isolado 2 apresentou crescimento micelial lento em placa de Petri e inibição contra L. gongylophorus, podendo este ser um isolado promissor em testes em campo.<br>The leaf-cutting ants (Hymenoptera: Formicidae), Atta and Acromyrmex genera, are the most important forest pests. They are found exclusively in Americas. Its economic importance is due to behavior to cut fresh plant material that serves as a substrate for the mutualistic symbiotic fungus Leucoagaricus gongylophorus (Basidiomycota: Agaricales) that are grown in underground chambers. Fertilized females are responsible for the founding of a new colony and they suffer direct influence of soil microorganisms. Therefore, newly fertilized females of Atta spp. should avoid fertile soils with high microbial load and even forested areas to found their nests. Entomopathogenic fungi and antagonists of L. gongylophorus are naturally present in the soil and they could be used in biological control of leaf-cutting ants. The objectives of this study were to evaluate and to compare the developing of young colonies of Atta sexdens in contact with soil from forested area and in contact with bare soils. Also, this and others procedures served to bioprospect antagonistic fungi of L. gongylophorus (Trichoderma spp.) from Gurupi region soil, and test the antagonistic effect of Trichoderma spp. against L. gongylophorus. In the first hours of start of experiments, Atta workers removed soil from colony recipients. This behavior could have favored colony survival, with a survival rate of 91,67 % during the 13 weeks. It was found that after the colonies have passed the critical period of foundation, the soil appears to exert little influence on the survival of workers and colonies. The soil from forested area had greater quantity and diversity of filamentous fungi than that from bare soil. The use of Tenebrio molitor as bait alive is efficient for bioprospecting by entomopathogenic fungi. All isolates of Trichoderma were able to inhibit in vitro growth of L. gongylophorus. Trichoderma spirale isolated 2 showed slow mycelial growth in Petri dish and strong level of inhibition against L. gongylophorus in vitro. So, this isolate is promising and should be tested in field.

Made available in DSpace on 2014-06-11T19:32:54Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-01-12Bitstream added on 2014-06-13T21:05:12Z : No. of bitstreams: 1 rodrigues_a_dr_rcla.pdf: 1112229 bytes, checksum: f59b4675edb860a1b20d6b5f1f7e6dc9 (MD5)<br>Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)<br>As formigas da tribo Attini são conhecidas pela complexa simbiose que mantêm com fungos, os quais cultivam como alimento. É sabido que além desse fungo, outros microrganismos podem ser encontrados nos ninhos desses insetos e estudos prévios apontaram que alguns microfungos (i.e. leveduras e fungos filamentosos) podem ser importantes nessa simbiose. O objetivo do presente trabalho foi avaliar o papel desses microfungos associados aos jardins dessas formigas. Analisando várias espécies do gênero Acromyrmex do sul do Brasil, demonstrou-se que as formigas importam uma comunidade diversa de microfungos para seus ninhos, provavelmente provenientes do solo e do substrato vegetal que as formigas utilizam para cultivar seu fungo. Num segundo estudo, avaliando formigas Attini da América do Norte (Atta texana, Trachymyrmex septentrionalis e Cyphomyrmex wheeleri) observou-se que a estrutura das comunidades de microfungos nos jardins desses insetos não se correlaciona com a variação sazonal, sugerindo que não existam relações espécie-específicas entre as formigas e os microfungos. Apesar de tais microrganismos não serem especialistas dos jardins desses insetos, é sugerido que os microfungos atuem como antagonistas do fungo simbionte. Ainda, descobriu-se que o parasita especializado Escovopsis spp. parece ser menos freqüente nas populações de formigas da América do Sul em relação as Attini da América Central, porém estudos adicionais são necessários para estabelecer a epidemiologia desse parasita nos ninhos das Attini. Num terceiro estudo, demonstrou-se que leveduras presentes nos jardins de fungos da formiga cortadeira A. texana inibem o crescimento de Escovopsis spp., sugerindo que esses insetos utilizam outros microrganismos, além das bactérias presentes em suas cutículas (Pseudonocardia spp.), para inibir esse parasita. Esse achado traz importantes implicações para essa...<br>Ants in the tribe Attini are well-known social insects that maintain a symbiotic relationship with fungi which they cultivate as food. Besides of the cultivated fungi, fungus gardens contain several other microorganisms considered to be potential players in this symbiosis. The aim of the present study was to evaluate the possible roles of microfungi (i.e. yeasts and filamentous fungi) in attine gardens. Our microbial profiling of gardens from several species in the genus Acromyrmex from South Brazil revealed that ants can harbor a diverse community of microfungi that probably originated from the surrounding soil or from the substrate used to manure the cultivated fungus. In this sense, additional studies of North American attine species (Atta texana, Trachymyrmex septentrionalis and Cyphomyrmex wheeleri) demonstrated that the structure of microfungal communities in gardens of these ants did not correlate with seasonal changes over a one year period, again suggesting there are no species-specific relationships among ants and microfungi species. Although, the microfungi are not specialized parasites of the attine ant-fungus symbiosis we suggest they can be considered antagonists to the cultivated fungus. Moreover, we demonstrated that the specialized parasite Escovopsis spp. is probably less frequent in South America than in Central America and we reinforce that additional studies are necessary to unravel the epidemiology of this parasite in attine gardens. In another study, we showed that yeasts isolated from gardens of the leafcutter ant A. texana can significantly inhibit the growth of Escovopsis sp. This interesting finding suggests that attine ants may use additional microbes to protect their gardens against Escovopsis spp. and not only actinomycete bacteria (Pseudonocardia spp.) found in their cuticles. Finally, we studied microfungi relationships with female alates (gynes) in two... (Complete abstract click electronic access below)

<p>Little is known about how the leaf bacterial community is affected by the seed microbiota at different stages of plant development. The bacterial populations of spinach seed and leaves after germination were compared using DGGE, to assess bacterial community richness, and real-time PCR to compare the abundance of select phyla (total bacteria, <i>Actinobacteria, Bacteroidetes, Firmicutes, α-Proteobacteria and β- Proteobacteria</i>). To determine the effect of environment, the plants were grown in the field and growth chambers. Vertical transmission of bacterial community members was evident; the developmental stage of the plant affected the richness and abundance of select bacterial phyla. The bacterial richness of plants grown in the two environments was not affected. However, overall numbers of bacteria increased in field grown samples in comparison to those produced in growth chambers during development. A statistically significant interaction was seen between growth stage and environment with each of the selected phyla. Populations on cotyledons were smaller than mature leaves, but were not significantly different than the 3-4 leaf stage plants. The culturable populations of bacteria on seeds (~5 log CFU/g) were significantly smaller than determined using real time PCR (~7 log copies). Of these bacteria cultured from spinach seeds, isolates belonging to the genera <i>Pantoea</i> were found to inhibit growth of <i>E. coli</i> O157:H7 <i>in vitro</i>. This study highlights the importance of vertical transmission on the bacterial community of plants and suggests the importance of developing strategies to influence these communities on seed to control human and plant pathogens on the leaf surface.</p><br>Master of Science in Life Sciences

Submitted by RAPHAEL VACCHI TRAVAGLINI null (raphatrava86@ig.com.br) on 2017-12-07T19:28:06Z No. of bitstreams: 1 RAPHAEL VACCHI TRAVAGLINI (1).pdf: 3425184 bytes, checksum: 732c0234a70c06bd049339e979dadab5 (MD5)<br>Approved for entry into archive by Maria Lucia Martins Frederico null (mlucia@fca.unesp.br) on 2017-12-08T11:14:08Z (GMT) No. of bitstreams: 1 travaglini_rv_bot_int.pdf: 3425184 bytes, checksum: 732c0234a70c06bd049339e979dadab5 (MD5)<br>Made available in DSpace on 2017-12-08T11:14:08Z (GMT). No. of bitstreams: 1 travaglini_rv_bot_int.pdf: 3425184 bytes, checksum: 732c0234a70c06bd049339e979dadab5 (MD5) Previous issue date: 2017-11-10<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>O controle biológico tem recebido atenção dos pesquisadores, principalmente devido aos movimentos, de preservação do ambiente. Têm sido amplamente aplicado em espécies consideradas importantes pragas agrícolas, porém não indicado para as formigas cortadeiras. Tais formigas apresentam um conjunto de estratégias físicas, químicas e comportamentais que as operárias realizam a fim de evitar a própria contaminação e da colônia. Entretanto alguns microorganismos conseguem causar mortalidade de alguns membros da colônia, como os fungos entomopatogênicos. Pretende-se fornecer conhecimentos básicos para desenvolvimento de novas estratégias de controle microbiano das formigas cortadeiras em um futuro próximo. Para tanto estudamos quatro fungos com grande potencial patogênico, Metarhizium anisopliae, Beauveria bassiana, Aspergillus flavus e Trichoderma asperellus. Primeiramente foram estudados a patogenicidade dos fungos (entomopatogeno e oportunista) em operarias isoladas da colônia. Estudou-se a susceptibilidade de larvas e adultos de formigas cortadeiras Atta sexdens rubropilosa a conídios de B. bassiana, por meio de técnicas histológicas e de microscopia. Finalmente encapsulados com conídios foram veiculados para o jardim de fungo simbionte visando o controle de mini colônias em laboratório. Propomos a elaboração de novas alternativas aos manejos existentes.

Leafy greens such as spinach have been the object of several recent food-borne pathogen outbreaks. The purpose of this study was to isolate bacteria spinach epiphytic bacteria that inhibit growth of E. coli O157:H7, which we describe as antagonism. The mechanism of antagonism was investigated and we attempted to improve the antagonistic potential in vitro and on spinach leaves when cellobiose, a carbon source utilized by the antagonists but not E. coli O157:H7, was added. There were larger culturable populations of bacteria on the leaves of savoyed cultivars compared to flat. From the isolated colonies, 47 displayed antagonism towards E.coli O157:H7, and were identified as members of 11 different genera and sixteen species. A representative isolate from each species was evaluated for three possible mechanisms of antagonism: acid production, secretion of an inhibitory compounds or secreted protease. The majority (14/16) produced at least a moderate level of acid. Two of these strains, Paenibacillus polymyxa and Pseudomonas espejiana, were found to secrete a non- protease antagonistic compound. These antagonists varied in their reduction of E.coli O157:H7 numbers in vitro, but all significantly reduced numbers in 48 hours of co-culturing in nutrient rich media. Five antagonists resulted in a significant reduction in E.coli O157:H7 populations when co-cultured on spinach leaves. Application of cellobiose did not improve the amount of antagonism in vitro or on the leaf surface after 24 hours.<br>Master of Science

LIMA, José Vinícius Leite. Populações microbianas e antagonismo de actinobactérias sobre rizóbios em solos do semiárido. 2017. 81 f. Tese (Doutorado em Ecologia e Recursos Naturais)-Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2017.<br>Submitted by ELAINE PEREIRA (ellainec.pereira@gmail.com) on 2017-09-19T17:31:18Z No. of bitstreams: 1 2017_tese_jvllima.pdf: 1448998 bytes, checksum: 2c2b1578a9568ad79222074a03a8f266 (MD5)<br>Approved for entry into archive by Jairo Viana (jairo@ufc.br) on 2017-09-22T17:59:28Z (GMT) No. of bitstreams: 1 2017_tese_jvllima.pdf: 1448998 bytes, checksum: 2c2b1578a9568ad79222074a03a8f266 (MD5)<br>Made available in DSpace on 2017-09-22T17:59:28Z (GMT). No. of bitstreams: 1 2017_tese_jvllima.pdf: 1448998 bytes, checksum: 2c2b1578a9568ad79222074a03a8f266 (MD5) Previous issue date: 2017<br>The structure of the communities living in the soil is driven by various mechanisms and the ecological interactions established between the living organisms. In the same way, the components of the microbiota present harmonic or non-harmonic relationships, for example, between actinobacteria and rhizobia. Interspecific competition among microorganisms occurs when many species require the same resources, and the negative effect on the availability of common resources adversely affects the others. In this context, the objective of this study was to quantify the microbial population in the soil and leaf litter in the vegetation of the caatinga and carrasco in the Brazilian semiarid region (Chapter I) and to characterize and evaluate the antagonistic effect of actinobacteria on rhizobia (Chapter II). The soil samples were collected at the Ecological Station of Aiuaba (Aiuaba, Ceará), characterized by the vegetation of caatinga and carrasco. In chapter I, the population density of the microbial community was evaluated by sampling of soil and litter in the vegetation of caatinga and carrasco at the Aiuaba Ecological Station. The microorganisms were isolated from the soil samples in flasks containing 0.8% saline solution and cultured, after consecutive dilutions, in culturing media specific to cultivable populations of total bacteria, actinobacteria, cellulolytic bacteria, phosphate solubilizing bacteria and fungi. Population estimation was then performed by standard counting on plates and the values were expressed in CFU.g-1. The microbial populations from the soil and leaf litter differed each other quantitatively and in the two vegetations, but in general were greater in the leaf litter. Thus, the knowledge of the population structure of the microbial community can be extended to the semiarid soils. In Chapter II, the strains of actinobacteria isolated in the first study were characterized and tested for “in vitro” inhibitory effect on strains of rhizobia also isolated from semiarid soils. The actinobacteria were purified in their respective culture medium (CDA medium). The strains were characterized for their color and morphology of the colonies, tolerance to pH levels, production of melanin and use of carbon sources. The “in vitro” antagonism of actinobacteria on rhizobia was evaluated in Petri dish containing yeast mannitol agar (YMA) medium by the formation of inhibition zone. The actinobacteria and rhizobia that had greater antagonistic effect or did not presented inhibition zones were molecularly identified. Sixty strains were identified in seven genera of actinobacteria in which had tolerance to variations in pH, low melanin production and generalist use of carbon sources. It was also observed “in vitro” antagonism of actinobacteria species, standing out the genus Streptomyces, on strains of Rhizobium tropici, Bradyrhizobium yuanmingense and two other rhizobia strains not identified. This is the first work that addresses this ecological interaction between microorganisms of the Brazilian semiarid region and reveals the occurrence of new species related to this negative interaction. Thus, the presence of antagonism among these organisms may lead to “in vivo” studies, contributing to future agricultural and/or ecological uses.<br>A estrutura das comunidades que vivem no solo é direcionada por vários mecanismos e as interações ecológicas estabelecidas entre os organismos. Da mesma forma, os componentes da microbiota apresentam relações harmônicas ou não entre si, como por exemplo, entre actinobactérias e rizóbios. A competição interespecífica entre os micro-organismos acontece quando muitas espécies procuram pelos mesmos recursos, e o efeito depressor que cada uma tem na disponibilidade dos recursos comuns afeta adversamente os outros. Neste contexto, teve-se como objetivo neste estudo quantificar em região semiárida a população microbiana no solo e serrapilheira nas fisionomias vegetais de caatinga e carrasco (Capítulo I) e caracterizar e avaliar o efeito antagônico de actinobactérias sobre rizóbios do semiárido (Capítulo II). O estudo foi realizado na Estação Ecológica de Aiuaba (Aiuaba, Ceará) caracterizada pelas fisionomias de caatinga e carrasco. No capítulo I, avaliou-se a densidade populacional da comunidade microbiana por meio de coleta de amostras do solo e serrapilheira nas fisionomias vegetais de caatinga e carrasco na Estação Ecológica de Aiuaba. Os micro-organismos foram isolados das amostras em solução salina 0,8% e cultivados, após diluições seriadas, em meios de cultura específicos para populações cultiváveis de bactérias totais, actinobactérias, bactérias celulolíticas, bactérias solubilizadoras de fosfato e fungos. Em seguida foi realizada a contagem das populações pela contagem padrão em placas usando a técnica de espalhamento em superfície, e os valores foram expressos em UFC.g-1. As populações microbianas oriundas do solo e serrapilheira diferiram quantitativamente entre elas e nas duas fisionomias vegetais, mas no geral foram maiores na serrapilheira. Dessa forma, pode-se ampliar o conhecimento da estrutura populacional da comunidade microbiana em solos de clima semiárido. No capítulo II, caracterizaram-se as cepas de actinobactérias isoladas das populações obtidas do primeiro estudo e testou-as para efeito inibidor in vitro sobre estirpes de rizóbios também oriundas de solos semiáridos. As actinobactérias foram purificadas no seu respectivo meio de cultura (meio CDA). As cepas foram caracterizadas quanto a atributos cromogênicos e morfológicos, para tolerância a níveis de pH, na produção de melanina e uso de fontes de carbono. O antagonismo das actinobactérias in vitro sobre rizóbios foi avaliado em meio de cultura ágar manitol levedura (YMA) pela formação de halo de inibição em placa de Petri. Em seguida, as actinobactérias e rizóbios que tiveram maior efeito antagônico ou que não formaram halo inibidor foram caracterizadas molecularmente. Foram obtidas 60 cepas identificados em sete gêneros de actinobactérias que tiveram tolerância a variações de pH, baixa produção de melanina e uso generalista de fontes de carbono. Foi observado antagonismo in vitro com formação de halo inibidor de espécies de actinobactérias, com destaque para o gênero Streptomyces, sobre os rizóbios Rhizobium tropici, Bradyrhizobium yuanmingense e outras duas estirpes não identificadas. Este é o primeiro trabalho que aborda essa relação ecológica em micro-organismos do semiárido e revela a ocorrência de novas espécies relacionados com essa interação negativa. Com isso, confirma-se a presença de antagonismo entre esses organismos que pode direcionar estudos de certificação in vivo, contribuindo para futuros usos agrícolas e/ou ecológicos.