PAH-degrading microorganisms capable to withstand the environmental stress conditions of Patagonia Central

MADUEÑO L.; ALVAREZ H. M.; MORELLI I. S.

Villa Carlos Paz

Congreso; VI Congreso Argentino de Microbiología General; 2009

Sociedad Argentina de Microbiologia General

Despite its long-term use in bioremediation, bioaugmentation of contaminated sites with microbial cells continues to be a source of controversy within environmental microbiology. Until now the strain selection has been based in a single criterion: degradation ability, with little or no consideration given to other essential features that are required to be functionally active or persistent in target habitats. In our Patagonia several environmental stresses, such as inorganic nutrients, water, pH and temperature, might limit the degradative activity of not adapted bacterial inoculum. The aim of this work was to study the resistance to different stress conditions of four autochthonous isolates (1A, 22A, 22B, and 36), belong to Sphingomonadaceae family, capable to degrade polycyclic aromatic hydrocarbons (PAH); and compared their stress response with that a PAH-degrading strain, Sphingomonas paucimobilis 20006FA, isolated from La Plata soil and phylogenetically closely related with the Patagonia strains. It was observed that, in batch culture, all the strains were capable to grow using phenanthrene as sole carbon and energy source, reaching a degradation of around 90% of phenanthrene supplied after 3 days of incubation. A different behavior was observed in case of fluorene, however none of the strain was capable of growing, the strain 1A and 36 showed a percentage of degradation significantly higher than the another strains. A microscope chemotaxis assay demonstrated chemotaxis positive response towards fluorene and phenanthrene. For C-starvation resistance testing, 5 ml of LMM (liquid mineral medium) was inoculated with 1x107 cfu/ml, in absence of FCE, and incubated at 28°C during 100 days. Periodically number of cfu/ml was determinated by counting on R2A medium. Whereas the S. paucimobilis 20006FA demonstrated to be the most sensitive strain to C-starvation, showing a reduction in the cfu/ml of two orders of magnitude at the end of the incubation time, the strains 22A and 22B maintained a relatively stable number of cfu/ml during the whole experiment. The strain 1A and 36 showed midway behavior. To measure the survival of the strains under water stress, drops of a cells suspension (DO600nm 4) were spotted onto Petri plates; the plates were incubated during 14 days at 28 °C and allowed to dry at a relative humidity of 17-18%. The survival rate was calculated as CFUafter drying/CFUbefore drying × 100. Clear differences were found between the strains. The strains 22A and 22B showed a highest survival rate, 72,6±1,29% and 82,2±2,31% respectively, whereas the strains 1A, 36, and S. paucimobilis 20006FA exhibited a survival rate below to of 60%. The results suggest the presence of mechanisms of adaptation to the typical environmental local conditions in the strains 22A and 22B, and they might be the most suitable strains for use as bacterial inoculum in PAH-contaminated soils of Central Patagonia.