Adaptation of Pseudomonas helmanticensis to fat hydrolysates and SDS: fatty acid response and aggregate formation

An essential part of designing any biotechnological process is examination of the physiological state of producer cells in different phases of cultivation. The main marker of a bacterial cell's state is its fatty acid (FA) profile, reflecting membrane lipid composition. Consideration of FA composition enables assessment of bacterial responses to cultivation conditions and helps biotechnologists understand the most significant factors impacting cellular metabolism. In this work, soil SDS-degrading Pseudomonas helmanticensis was studied at the fatty acid profile level, including analysis of rearrangement between planktonic and aggregated forms. The set of substrates included fat hydrolysates, SDS, and their mixtures with glucose. Such media are useful in bioplastic production since they can help incrementally lower overall costs. Conventional gas chromatography-mass spectrometry was used for FA analysis. Acridine orange-stained aggregates were observed by epifluorescence microscopy. The bacterium was shown to change fatty acid composition in the presence of hydrolyzed fats or SDS. These changes seem to be driven by the depletion of metabolizable substrates in the culture medium. Cell aggregation has also been found to be a defense strategy, particularly with anionic surfactant (SDS) exposure. It was shown that simple fluidity indices (such as saturated/unsaturated FA ratios) do not always sufficiently characterize a cell's physiological state, and morphological examination is essential in cases where complex carbon sources are used.