Plants and microorganisms exhibit complex interactions Bioprospecting in such areas could be interesting for with the environment and produce small molecules, natural industrial applications, because organisms growing and products useful for their survival. As a consequence of their producing bioactive substances under these conditions may biological role, these metabolites might exhibit a broad be able to achieve better yields. range of biological activities. In fact, natural products have Furthermore, biosurfactants have many advantages played a fundamental role in useful bioactive substances for when compared to synthetic surfactants. They may be more industrial applications (Pupo et al. 2006). Isolation of such stable at the extreme conditions of oil reservoirs, less toxic, microorganisms can lead novel bioactive natural products biodegradable, and show better efficiency for oil recovery. research for oil, pharmaceutical, and agrochemical Another advantage of biosurfactants is that they can be industries (Strobel 2006). modified by biotransformation to generate new products for The semi-arid region of the state of Bahia, especially the specific requirements (Deleu & Paquot 2004). However, Chapada Diamantina, presents one of the most diverse studies associated with its production in different culture ecosystems of the biosphere (Torres et al. 2003). The media and physicochemical conditions are necessary to biodiversity of Chapada Diamantina presents achieve the best competitive advantages (Mulligan 2005). microorganisms with biotechnological features applicable Biosurfactant production depends primarily on microbial to oil industries due to the extreme conditions of its strain, carbon and nitrogen sources, pH, temperature, environment, such as highly saline, nutrient-poor and oxygen, and metal ion concentrations. Addition of water- extremely acidic soils, in addition to its higher immiscible substrates to media as long as nitrogen and iron environmental temperatures (Gusmão & Maia 2006). limitations in the media results in an overproduction of some biosurfactants. The most promising applications are cleaning of oil-contaminated tankers, oil spill management, recovery of crude oil from sludge, enhanced oil recovery, and bioremediation of sites contaminated with Sitientibus série Ciências Biológicas 12(1): 157–163. 2012. Biosurfactant production from Pseudomonas strains isolated in rhizospheric soils from semi-arid area of Bahia, Brazil 1* 1 1 Sidnei Cerqueira dos Santos ,∙Lidiane Karla Xisto Oliveira , Suikinai Nobre Santos , Narah Pinheiro 2 3 5 4 Cabral Santos , Cristina M. Quintella , Paulo Fernando de Almeida , Luzimar Gonzaga Fernandez , Juan 2 1,5 Carlos Rossi-Alva & Milton Ricardo de Abreu Roque 1 Programa de Pós-graduação em Biotecnologia, Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Bahia, Brazil. 2 Laboratório de Estudos em Meio Ambiente, Superintendência de Pesquisa e Pós-graduação, Universidade Católica do Salvador, Bahia, Brazil. 3 4 Laboratório de Cinética e Dinâmica Molecular, Departamento de Química; Laboratório de Bioquímica, Biotecnologia e 5 Bioenergia, Instituto de Ciências da Saúde, Departamento de Biofunção; e Laboratório de Ecologia e Biotecnologia de Microrganismos, Instituto de Ciências da Saúde, Departamento de Biointeração. Universidade Federal da Bahia, Bahia, Brazil. Abstract – The aim of this study was to select biosurfactant-producing bacterial strains from soils of plants in the semi-arid region of the state of Bahia, Brazil. The mineral salt medium (MSM) was used as base medium, changes being made in the glucose concentration, temperature, and pH during the optimization process. Two biosurfactant-producing bacterial strains were isolated from the soil of Actinocephalus sp. and belonged to the genus Pseudomonas. The emulsification indexes of these strains rose until 58%. They reduced surface and interfacial tensions of culture medium and crude oil to less than 33 mN/m and 3 mN/m, respectively. This study represented an unprecedented discovery of surfactant activity of the bacterial strains isolated from rhizospheric soils of plants from Northeast Brazilian semi-arid region. Additional key words: bacterial, plants. Resumo (Produção de biossurfactante por linhagens de Pseudomonas isoladas do solo rizosférico no Semiárido da Bahia, Brasil) – O objetivo deste estudo foi selecionar linhagens bacterianas produtoras de biossurfactante do solo rizosférico de plantas na região semiárida do estado da Bahia, Brasil. O meio salino mineral (MSM) foi usado como meio base, sendo realizadas mudanças na concentração de glicose, temperatura e pH durante o processo de otimização. Duas linhagens produtoras de biossurfactante foram isoladas do solo rizosférico de Actinocephalus sp. e pertencem ao gênero Pseudomonas. Os índices de emulsificação destas linhagens aumentaram até 58%. Elas reduziram as tensões superficial e interfacial do meio de cultura e do óleo cru para menos de 33 mN/m e 3 mN/m, respectivamente. Este estudo representou uma descoberta inédita da atividade surfactante de linhagens bacterianas isoladas de solo rizosférico de plantas da região semiárida no Nordeste Brasileiro. Palavras-chave adicionais: bactérias, plantas. * Author for correspondence: sidneibio@yahoo.com.br Communicating editor: Siddhartha Georges Valadares Almeida de Oliveira Costa Submitted in: 21 Feb. 2011; online publication: 12 June 2012