Aggregation experiments were performed as described by
Golowczyc et al. (2009) with modifications. The washed microbial
pellets were suspended in different saline solutions previously
adjusting to specified pH values of 4.2 and 6.2 using 1 M NaOH or HCl
solutions. In all experiments, the final concentrations of the microbial
suspensions were adjusted to OD600 ¼ 1.00 0.02 as measured by
a spectrophotometer (Genesys 10S, Thermo Spectronic, Rochester,
NY). For the auto-aggregation assay, one milliliter microbial
suspension was added to a cuvette and the optical density at 600 nm
was measured statically at regular intervals. The percentage autoaggregation
was expressed as follows (Equation (1)):
% Auto-aggregation ¼ ðODi ODtÞ=ODi 100 (1)
Where ODi is initial optical density of microbial suspension, and
ODt is the optical density after time t.
For the co-aggregation experiments, one half milliliter bacterial
suspension and yeast suspension were mixed in a cuvette and the
optical density at 600 nm was measured statically at regular
intervals. The percent co-aggregation was expressed as follows
(Equation (2)):
% Co-aggregation ¼ ½ðOD1 þ OD2Þ 2ODt=ðOD1 þ OD2Þ 100
(2)
OD1: optical density of strain 1, OD2: optical density of strain 2,
ODt: optical density of strain 1 and strain 2 after t time.