Colony morphology and transcriptome profiling of Pseudomonas putida KT2440 and its mutants deficient in alginate or all EPS synthesis under controlled matric potentials

Pseudomonas putida is a versatile bacterial species adapted to soil and its fluctuations. Like many other species living in soil, P. putida often faces water limitation. Alginate, an exopolysaccharide (EPS) produced by P. putida, is known to create hydrated environments and alleviate the effect of water limitation. In
addition to alginate, P. putida is capable of producing cellulose (bcs), putida
exopolysaccharide a (pea), and putida exopolysaccharide b (peb). However,
unlike alginate, not much is known about their roles under water limitation.
Hence, in this study we examined the role of different EPS components under
mild water limitation. To create environmentally realistic water limited conditions
as observed in soil, we used the Pressurized Porous Surface Model. Our
main hypothesis was that under water limitation and in the absence of alginate
other exopolysaccharides would be more active to maintain homeostasis. To
test our hypothesis, we investigated colony morphologies and whole genome
transcriptomes of P. putida KT2440 wild type and its mutants deficient in
synthesis of either alginate or all known EPS. Overall our results support that
alginate is an important exopolysaccharide under water limitation and in the
absence of alginate other tolerance mechanisms are activated.