BACKGROUND: The facile use of microorganisms as green templates for shape-control of Au nanostructures can not only utilize their characteristic nanoscale dimensions and versatility, but also bridge the gap between bulk materials and Au nanostructures for technical applications. RESULTS: Using Escherichia coli cells (ECCs), closely packed, hierarchically branched, chemically difficult-to-synthesize and stable Au nanowires (AuNWs) were fabricated through a seedless microorganism-mediated, hexadecyltrimethylammonium bromides (CTAB)-directed method. The ECCs played dual roles in the biosorption of Au ions and acted as preferential nucleation sites for Au nanocrystals in the formation of the AuNWs. In addition, proper CTAB concentration and just a little excessive ascorbic acid were essential to the formation of the AuNWs. The preferential nucleation sites that were simultaneously mediated by adjacent cells favored branched growth. Random growth of the same nanowire with multiple branched points gave rise to hierarchically branched AuNWs. Interestingly, the AuNW/ECC nanocomposites exhibited a noticeable absorbance at around 1900 nm in the near-infrared (NIR) region. CONCLUSION: This study verifies the general strategy by combining a microorganism and CTAB for the fabrication of functional AuNW/microorganism nanocomposites. (C) 2013 Society of Chemical Industry