CHANGE IN VOLUME AND MORPHOLOGY IN CULTURES OF OLEISPIRA ANTARCTICA AS A FUNCTION OF TEMPERATURE AND SUBSTRATES USED

Bacterial population under nutritional and physic stress react in order to adequate cell metabolism and physiology to stressful conditions. One of the most frequently observed behaviours in the stress-starvation response of gram-negative bacteria is the size reduction and cell morphology conversion from rod to resistant shape-form. In such framework, we report here on morphology (cell volume and cell shape) variations in psychrophilic strain Oleispira antarctica RB 8T under different growth temperature and different hydrocarbons mixtures sources. Six different hydrocarbons mixtures (car commercial diesel, commercial crude oil engine; 2 different bilge waters, military jet fuel and crude oil) were used as single carbon source and two different cultivation temperatures (4° and 15°C) were tested for 22 days. During incubation period, sub-aliquots of each bacterial culture were processed to estimate total bacterial abundance (DAPI count), variation of cell volume and morphological diversity (determination from digital photomicrographs using an image analysis program). Total bacterial abundance by DAPI staining showed an increase at both temperatures and in almost all substrates used in the first 18 days of experiment; after, values of bacterial abundance by DAPI counts showed a decrement of almost all cultures at both incubation temperatures. Overall, the mean cell volume decreased with increasing of temperature. Three morphological types of bacteria were identified: spiral bacteria (spirillae and curved rods), cocci and rods. The morphological analysis revealed that the spiral bacteria forms changed significantly in coccoid and rods shapes, in relation with the added substrates, except for the bilge waters, where spiral bacteria were mostly the dominant shape. The study of morphological and physiological variation of hydrocarbonoclastic bacteria is a fundamental topic for the study of their potential use in the mitigation of oil spills phenomenon in cold environment.