Table 2.

Capacity of Antarctic strains to produce MVs, form biofilms and secrete eATP. To determine MV concentration and eATP, strains were grown on TSB for 48 h at 15 °C and 180 rpm. For biofilm formation, strains were grown on 96-well plates at 15 °C without shaking for 6 days

Strain	MVa (mg/ml LPS)	Biofilmb	eATPc
Shewanella vesiculosa M7T	2.573	++	++
Shewanella frigidimarina NF12	1.098	+	–
Shewanella livingstonensis NF22T	3.421	+	–
Psychrobacter fozii NF23T	0.014	+	+++
Psychrobacter glacincola NF1	0.001	+	+
Psychrobacter immobilis NF18	0.001	+++	++
Psychrobacter luti NF11T	0.073	+++	+
Pseudomonas sp. ID1	0.065	+++	–
Pseudoalteromonas M2	–	+	++
Pseudoalteromonas M4–1	2.051	+	–
Pseudomonas aeruginosa PAO1	ND	++	ND

^aMVs were collected from 1 L cultures and quantified by LPS concentration using the Purpald Assay protocol

^bBiofilm formation was determined by the crystal violet method. To interpret the results, an OD threshold at which biofilm is formed was established. A strain is biofilm-forming if OD levels exceed the OD of the negative control plus three times its standard deviation (SD) [OD threshold = OD negative control + 3 × SD]. Strains can be divided into 4 categories: the strain is not biofilm-forming (−) if the OD is less than or equal to the OD threshold; a weak biofilm producer (+) if the OD is greater than and less than twice the OD threshold; moderately biofilm-forming (++) if the OD is greater than twice and less than four times the OD threshold; and a strong biofilm producer (+++) if the OD is greater than four times the OD threshold

^ceATP from cultures (OD = 2.2) was determined from 0.22 μm-filtered supernatant broths and bioluminescence was measured by a BacTiter-Glo Microbial Cell Viability Assay (Promega). For a simpler interpretation, “−”was assigned to bacteria that exported less than 1 nM to the supernatant; “+” between 1 nM and 10 nM; “++” between 10 nM and 100 nM; and “+++” for more than 100 nM