BIOFILMS ON SUBMERGED RIVER RED GUM (EUCALYPTUS-CAMALDULENSIS DEHNH MYRTACEAE) WOOD IN BILLABONGS - AN ANALYSIS OF BACTERIAL ASSEMBLAGES USING PHOSPHOLIPID PROFILES

Biofilms were allowed to develop on wooden slides of the River Red Gum (Eucalyptus camaldulensis Dehnh., Myrtaceae) submerged in two billabo ngs of south-eastern Australia. The slides were placed in the photic z one and the aphotic zone, and the biofilms sampled after eight week's growth over the summer of 1989-1990 and winter of 1990. Bacterial numb ers, estimated with epifluorescence microscopy, ranged from 4-78 x 10( 6) cells cm-2. Bacteria were more abundant in the photic zone than the aphotic zone, and more abundant in summer than winter. Fewer than 0.5 % of the bacteria could be cultivated on nutrient agar plates. Concent rations of phospholipids ranged from 8-79 ng cm-2, which corresponded to bacterial abundances of 2-17 x 10(6) cells cm-2. Fifty five phospho lipid fatty acids (PLFA) were identified, of which 16:0 (13-29% of tot al PFLA) was the most common. Other abundant PFLA included 16:1omega7c (6-28%), 18:2omega6 (3-16%), 18:3omega3 (4-12%), 18:1omega9c (3-5%), 18:1omega7c (5-11%) and 18:0 (2-8%). Minor PLFA included 14:0, i and a 15:0, 15:0, 16:1omega5c, 16:1omega13c, 18:3omega6, 18:4omega3, 20:4om ega6 and 20:5omega3. The PLFA profiles of the biofilms were quite diff erent from those of the sediments and plankton. There was a clear dist inction between the PLFA profiles of summer and winter biofilms, but l ess evidence for unequivocal site or light-regime effects.