The cold adaptability of microorganisms with different carbon source under 5 degrees C was studied in activated sludge for treating synthetical wastewater. Phospholipid fatty acid (PLFA) analysis indicated contents of unsaturated fatty acids in cell membrane at 5 degrees C were 13.66% and 24.96% higher for glucose and sodium acetate source than that at 25 degrees C. PLFA biomarkers showed more Gram-negative bacteria enriched than Gram-positive bacteria in low-temperature activated sludge. The Shannon-Wiener diversity analysis demonstrated glucose fed reactor in low temperature had lower PLFA diversity index (1.21-1.30) than that at 25 degrees C and sodium acetate source was reverse (1.08-0.69). The 16S rRNA analysis manifested certain microbes were considerably suitable for existence under cold environment, most of which belong to Gram-negative bacteria. (C) 2012 Elsevier Ltd. All rights reserved.