Occurrence and diversity of Ralstonia solanacearum populations in Brazil / Ocorrência e diversidade de populações de Ralstonia solanacearum no Brasil

Ralstonia solanacearum is a gram-negative soil-borne bacterium capable of infection of hundreds of vegetable species over more than 50 botanical families, causing bacterial wilt, except for bananas, when the disease is called Moko. It deserves special attention, from all other plant pathogenic bacteria, for its high phenotypic and genotypic plasticity, a characteristic that makes disease control extremely difficult. In this context, frequent and necessary surveys are conduct in the attempt of characterizing the prevailing strains of R. solanacearum in each region where the disease has been reported. However, knowledge about occurrence and diversity of R. solanacearum in Brazil is fragmented and in some cases, based on inconclusive studies with few strains, little representative of a given region. The need to obtain a greater picture guided this review. The occurrence of this bacterium in Brazilian States and the possible causes for its dissemination are presented, with emphasis on studies of genetic variability of populations of R. solanacearum in the country. The compiled results report a wide distribution of the bacterium in Brazil and great variability of its populations among locations. Partly due to the difficulty of detecting small titer of bacteria in samples, paucity of information about the origin of inoculum in certain regions is observed, as well as the need for detecting the presence of the pathogen in asymptomatic plants, potato tubers with latent infections, soil, and water, which are the major causes of bacterial dissemination into areas without any disease history.

Ralstonia solanacearum é uma bactéria gram-negativa habitante do solo capaz de infectar centenas de espécies vegetais distribuídas em mais de 50 famílias botânicas, onde causa a murcha-bacteriana, exceto na bananeira, na qual recebe o nome de Moko. Destaca-se entre outras bactérias fitopatogênicas pela sua alta plasticidade fenotípica e genotípica, característica que contribui sobremaneira para dificultar o controle da doença. Nesse contexto, levantamentos frequentes e necessários são conduzidos na tentativa de caracterizar isolados de R. solanacearum prevalentes em cada região onde a doença tem sido relatada. No Brasil, o conhecimento sobre a ocorrência e a variabilidade de R. solanacearum está fragmentado e, em alguns casos, baseado em estudos inconclusivos pelo uso de amostras de isolados pouco representativas de uma região. A necessidade de agrupar essas informações norteou a presente revisão de literatura. A ocorrência da bactéria nos Estados brasileiros e as possíveis causas de sua disseminação são apresentadas, com ênfase nos estudos da variabilidade genética das populações de R. solanacearum no país de acordo com o atual esquema de classificação da bactéria. Os resultados de pesquisa compilados da literatura reportam ampla distribuição da bactéria no Brasil e grande variabilidade de suas populações entre locais. Em parte devido à dificuldade de detectar pequenos números de células bacterianas em amostras, nota-se escassez de informações sobre a origem do inóculo em determinadas regiões, bem como a necessidade de detectar a presença do patógeno em plantas assintomáticas, em tubérculos de batata com infecções latentes, no solo e na água, que são as principais causas da disseminação da bactéria para áreas sem histórico da doença.

Molecular identification of methanogenic archaea from Surti buffaloes (bubalus bubalis), reveals more hydrogenotrophic methanogens phylotypes

Methane emissions from ruminant livestock are considered to be one of the more potent forms of greenhouses gases contributing to global warming. Many strategies to reduce emissions are targeting the methanogens that inhabit the rumen, but such an approach can only be successful if it targets all the major groups of ruminant methanogens. Therefore, a thorough knowledge of the diversity of these microbes in breeds of buffaloes, as well as in response to geographical location and different diets, is required. Therefore, molecular diversity of rumen methanogens in Surti buffaloes was investigated using 16S rRNA gene libraries prepared from pooled rumen contents from three Surti buffaloes. A total of 171 clones were identified revealing 23 different sequences (phylotypes). Of these 23 sequences, twelve sequences (12 OTUs, 83 clones) and 10 sequences (10 OTUs, 83 clones) were similar to methanogens belonging to the orders Methanomicrobiales and Methanobacteriales, and the remaining 1 phylotype (5 clones) were similar to Methanosarcina barkeri. These unique sequences clustered within a distinct and strongly supported phylogenetic group. Further studies and effective strategies can be made to inhibit the growth of Methanomicrobiales and Methanobacteriales phylotypes to reduce the methane emission from rumen and thus help in preventing global warming.