CONICET | Buscador de Institutos y Recursos Humanos

P. extremaustralis is a versatile Antarctic bacterium able to grow under aerobic and microaerobicconditions and is related to several non-pathogenic Pseudomonads. An interesting characteristic of P.extremaustralis is its capability to accumulate polyhydroxyalkanoates (PHAs) as polyhydroxybutyrate(PHB) and medium chain length PHA under unbalanced nutritional conditions. PHAs accumulationwas shown to be related with P. extremaustralis high resistance to environmental stress, having alsobiotechnological interest by its properties similar to petroleum derived plastics. Due that changes inthe medium pH could be considered as a stress factor the aim of this work was to analyze the effect ofdifferent pH in P. extremaustralis growth and how pH affects PHAs accumulation.To study the effect of pH in P. extremaustralis growth, overnight precultures performed in LBmedium supplemented with 0.25% sodium octanoate, to favor PHA accumulation, were used toinoculate fresh culture medium in which pH was adjusted to different values (5.5, 6, 7, 8, 9, 9.5 and10). Initial OD600nm was 0.05 (about 1x10 7 CFU/ml). Cultures were incubated at 30°C and 200 rpmfor 24h. After incubation time, growth was measured by both OD and viable (CFU/ml) counts.Qualitative PHA accumulation was analyzed by Nile blue staining and microscopy observation.Quantitative PHA content was determined by gas chromatography. Experiments were performed using3 independent cultures.Our results showed strong differences in the growth of the cells at different pH. Marked loss ofviability at pH 5.5 was observed. The initial bacterial number decreased immediately 3 orders ofmagnitude (from about 10 7 CFU/ml to 10 3 CFU/ml) and no viable cells were detected after 24hincubation. On the other hand, P. extremaustralis was able to grow when pH ranging between 6 to 9,showing a high increase in viable cell number and PHA content. For cultures grown at alkaline pHbetween 9 to 10, a decrease in viability of around two orders of magnitude in comparison with initialcounts was observed and an increasing cell size associated to a greater PHAs synthesis was observed.Results showed that both acidic and alkaline pH affected growth of P. extremaustralis, howeveralkaline suboptimal growth conditions resulted in higher PHA accumulation.These results suggest that PHA conferred to P. extremaustralis an adaptive advantage, enabling it tosurvive under suboptimal conditions for growth. In addition, information regarding conditions leadingto higher PHA accumulation can be useful to improve the design of strategies for bioplasticsproduction