Diversidade e distribuição de cianobactérias de crostas biológicas do bioma caatinga com base em taxonomia polifásica e análise metagenômica
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Data
2020-09-30
Autores
Lima, Nathali Maria Machado
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Universidade Estadual Paulista (Unesp)
Resumo
Crostas biológicas (CBs) consistem em uma comunidade de elementos entrelaçados composta por organismos poiquiloídricos, como cianobactérias, algas verdes, microfungos, bactérias, líquens, musgos e microartrópodes. Estas comunidades exercem funções ecológicas importantes e ocorrem nas camadas superficiais do solo, em uma variedade de regiões climáticas ao redor do globo, principalmente em regiões áridas e semiáridas. As cianobactérias são componentes de extrema importância nessas comunidades, sendo consideradas pioneiras e responsáveis por estruturar a camada superior do solo, tornando possível a colonização por outros grupos. Embora as cianobactérias de CBs venham sendo bem estudadas, ainda há muita diversidade não acessada, principalmente na América do Sul. No Brasil, estes estudos estão praticamente restritos às regiões de Cerrado e os dados que foram encontrados até o momento ressaltam a necessidade de ampliação de estudos no país para que também haja o preenchimento de vazio de conhecimento em outros biomas. Dessa forma, a Caatinga, que é um ambiente restritivo, considerada uma das áreas mais quentes entre as regiões semiáridas do mundo e portanto, propício à presença de crostas biológicas, foi escolhida para ser explorada. As coletas foram feitas nos municípios de Cabaceiras, Barra de Santa Rosa e Pocinhos (Paraíba) em quatro localidades, onde amostras das crostas foram recolhidas segundo à metodologia padrão, ao longo de transeções de 200 m. Foram coletadas 10 amostras de crostas em cada local amostrado e também recolhidas porções de solo para a realização de análises de parâmetros físicos e químicos, como nitrogênio total, fósforo total, ortofosfato, matéria orgânica, pH, carbono orgânico e textura do solo. Temperatura, umidade relativa do ar e irradiância foram parâmetros medidos diretamente em campo. Uma parcela de solo de cada amostra foi separada e analisada quanto à presença de cianobactérias, e para cada população registrada foram feitas análises morfológicas e cultivos. Outra parcela de solo de cada amostra foi inoculada em meio de cultura, visando o estabelecimento de culturas de cianobactérias que não tivessem sido observadas anteriormente. As populações cultivadas e consideradas unicianobacteriais tiveram seus materiais genéticos acessados por meio de extração, amplificação e sequenciamento. A última parcela de solo da amostra seguiu para análises metagenômicas, por meio de extração, amplificação e tecnologia de sequenciamento de próxima geração. Foram estudadas 26 populações, sendo nove a partir de amostras provenientes da natureza e outras 17 provenientes de cultivo e analisadas por critérios morfológicos e moleculares. Em todas as quatro localidades estudadas foram encontradas populações de Scytonema e Microcoleus, além de Nostoc também ter sido registrada em três das quatro regiões. Microcoleus e Nostoc foram analisados separadamente, por meio de estudos detalhados de filogenia e resultaram no descrição de seis novos gêneros e 12 novas espécies. A análise de NGS possibilitou uma investigação ecológica, que relacionou a distribuição dos grupos de cianobactérias registradas a fatores ambientais, e também a comparação entre Caatinga e outro bioma propício à formação de crostas, o Pampa. A composição de cianobactérias registrada na Caatinga evidenciou a dominância de organismos adaptados à sobrevivência em ambiente com altas temperaturas e níveis de irradiância. Comumente encontrados em crostas em estágio de desenvolvimento avançado e apresentando uma relação positiva com compostos químicos essenciais para o solo, como fósforo e nitrogênio. Enfatizando assim, a importância das cianobactérias na nutrição dos solos e na consequente criação de condições favoráveis para o estabelecimento de organismos superiores. Como apêndice foram apresentados dados de um estudo realizado em parceria com um laboratório na Austrália. Neste trabalho foram aplicadas técnicas recentes que utilizam cianobactérias provenientes de crostas biológicas na conservação e restauração de espécies de plantas nativas.
Biological soil crusts (BSCs or biocrusts) consist of a community of elements that are interwoven and composed of poikilohydric organisms such as cyanobacteria, green algae, bacteria, lichens, mosses and microarthropods. These communities, which inhabit the top few centimeters of the soil, are responsible for important ecological functions. Biocrusts cover large parts of the soil surface in a broad range of habitats from a variety of climatic regions around the globe, mainly in arid and semiarid areas. Cyanobacteria are extremely important components of these communities, being considered their pioneers and responsible for structuring the soil biocrust and preparing it for the colonization by other organisms. Even though cyanobacteria from BSCs have been relatively well studied, a large part of their diversity is still unknown, especially in South America. Studies in Brazil are nearly restricted to the Cerrado region and data found so far highlights the need of further research in the country to improve knowledge from other biomes. Therefore, this study focused on the Caatinga biome, an extreme environment considered one of the hottest regions among the semiarid regions in the globe, being favorable to the presence of BSCs are broadly present. Sampling was carried out in the three cities: Cabaceiras, Barra de Santa Rosa and Pocinhos (Paraiba state) in four different localities, where biocrusts were sampled along 200 m transects following standard protocols. At each locality, a total of 10 samples were sampled, with an extra amount of soil collected for physical and chemical analysis, e.g. total nitrogen, total phosphate, organic matter, pH, organic carbon and soil texture. Temperature, air relative humidity and irradiance were measured in the field. Each soil sample was divided into three subsamples; the first one was used for the analyses of cyanobacteria populations, which were cultured and morphologically examined. A second subsample was inoculated in BG11 medium to promote the development of populations not observed before. The unicyanobacterial cultures had their DNA material extracted, amplified, and sequenced. The last subsample of each soil sample was used for metagenomic analyses, with extraction, amplification and sequencing through next-generation sequence technologies (NGS). We studied 26 populations, nine of which were observed directly after sampling, and 17 were cultivated and analyzed through morphological and molecular methods. Scytonema and Microcoleus were found in all the four studied localities, while Nostoc was registered in three of them. Nostoc and Microcoleus were submitted to a deep phylogenetic evaluation that resulted in the proposition of six new genera and 12 new species. The NGS analysis allowed an ecological investigation, relating the distribution of the registered cyanobacteria with environmental factors. It made possible the comparison among Caatinga and another biome suitable to the development of biocrusts, called Pampa. The registered cyanobacterial composition in Caatinga was evidence that the dominant cyanobacteria were able to activate chemical pathways that allow their survival under high temperatures and high levels of irradiance. This group is common to biocrusts in a late stage of development and presents a positive relation with essential chemical compounds to the soil, e.g. phosphorus and nitrogen. This record highlights the importance of these communities inpromoting a nutritional rich soil system able to harbor bigger organisms. The last componentof this thesis brings results of a project developed in collaboration with an internationalresearch group in Australia. This study applied novel techniques harnessing cyanobacteriafrom biological soil crusts for promoting the conservation and restoration of native plants.
Biological soil crusts (BSCs or biocrusts) consist of a community of elements that are interwoven and composed of poikilohydric organisms such as cyanobacteria, green algae, bacteria, lichens, mosses and microarthropods. These communities, which inhabit the top few centimeters of the soil, are responsible for important ecological functions. Biocrusts cover large parts of the soil surface in a broad range of habitats from a variety of climatic regions around the globe, mainly in arid and semiarid areas. Cyanobacteria are extremely important components of these communities, being considered their pioneers and responsible for structuring the soil biocrust and preparing it for the colonization by other organisms. Even though cyanobacteria from BSCs have been relatively well studied, a large part of their diversity is still unknown, especially in South America. Studies in Brazil are nearly restricted to the Cerrado region and data found so far highlights the need of further research in the country to improve knowledge from other biomes. Therefore, this study focused on the Caatinga biome, an extreme environment considered one of the hottest regions among the semiarid regions in the globe, being favorable to the presence of BSCs are broadly present. Sampling was carried out in the three cities: Cabaceiras, Barra de Santa Rosa and Pocinhos (Paraiba state) in four different localities, where biocrusts were sampled along 200 m transects following standard protocols. At each locality, a total of 10 samples were sampled, with an extra amount of soil collected for physical and chemical analysis, e.g. total nitrogen, total phosphate, organic matter, pH, organic carbon and soil texture. Temperature, air relative humidity and irradiance were measured in the field. Each soil sample was divided into three subsamples; the first one was used for the analyses of cyanobacteria populations, which were cultured and morphologically examined. A second subsample was inoculated in BG11 medium to promote the development of populations not observed before. The unicyanobacterial cultures had their DNA material extracted, amplified, and sequenced. The last subsample of each soil sample was used for metagenomic analyses, with extraction, amplification and sequencing through next-generation sequence technologies (NGS). We studied 26 populations, nine of which were observed directly after sampling, and 17 were cultivated and analyzed through morphological and molecular methods. Scytonema and Microcoleus were found in all the four studied localities, while Nostoc was registered in three of them. Nostoc and Microcoleus were submitted to a deep phylogenetic evaluation that resulted in the proposition of six new genera and 12 new species. The NGS analysis allowed an ecological investigation, relating the distribution of the registered cyanobacteria with environmental factors. It made possible the comparison among Caatinga and another biome suitable to the development of biocrusts, called Pampa. The registered cyanobacterial composition in Caatinga was evidence that the dominant cyanobacteria were able to activate chemical pathways that allow their survival under high temperatures and high levels of irradiance. This group is common to biocrusts in a late stage of development and presents a positive relation with essential chemical compounds to the soil, e.g. phosphorus and nitrogen. This record highlights the importance of these communities inpromoting a nutritional rich soil system able to harbor bigger organisms. The last componentof this thesis brings results of a project developed in collaboration with an internationalresearch group in Australia. This study applied novel techniques harnessing cyanobacteriafrom biological soil crusts for promoting the conservation and restoration of native plants.
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Palavras-chave
Crostas biológicas, Ambientes restritivos, Diversidade em crostas, Bactérias fotossintetizantes., Biological soil crusts, Extreme environments, Biocrust diversity, Photosynthetic bacteria