Streak plating

This is a suitable method for small species (<10 mm) or algae that grow well on a substrate.

1. Equipment

  • Petri dish — sterile, disposable, 90 mm diameter
  • Media — e.g. f2
  • Agar — Bacto-Agar, Difco, Cat. No. 0140—01
  • Wire loops — nichcrome or platinum
  • Bunsen burner or small flame
  • Parafilm

2. Method

  • Prepare petri dishes containing growth medium solidified with 1-1.5% agar medium. The agar should be 1/22/3 the depth of the dish.
  • Place 1—2 drops of mixed phytoplankton sample near the periphery of the agar. Flame sterilize a wire loop. Using aseptic technique use the sterile loop to make parallel streaks of the suspension on the agar. Note that there are 16 streaks (4 sets of 4) to be made and the whole surface of the agar plate is used (see fig below).
  • Cover and seal plate with parafilm. Invert and incubate under low light at constant temperature.
  • Select colonies that are free of other organisms for further isolation. Remove a sample using a sterilized wire loop and place in a drop of sterile culture medium on a glass slide. Check microscopically that the desired species has been isolated and is unialgal.
  • Repeat the streaking procedure with the algal cells from a single colony and again allow colonies to develop. This second streaking reduces the possibility of bacterial contamination and of colonies containing more than one algal species.
  • Transfer selected colonies to liquid or agar medium.

Fig Streak plating with wire loop