For analysis by GC-MS, 0.5 ml of culture supernatant was acidified
with 50 ml 1 M HCl and extracted with 1 ml of chloroform/methanol
(1 : 1) (Mayer & Shanklin, 2007) using heptanoic acid as an extraction
control where indicated. The organic phase (1 ml) was injected onto an
Agilent 6890 Series gas chromatograph equipped with an Agilent HP-
5MS column and an Agilent single quadrupole 5973 mass spectrometer
using electron ionization. The method used a splitless injection
with a 50 ml min21 flow rate and helium as the carrier gas, and a mean
velocity of 36 cm s21
. Oven temperature and run times were identical
to GC flame-ionization detector analysis described above.