http://informahealthcare.com/bty ISSN: 0738-8551 (print), 1549-7801 (electronic) Crit Rev Biotechnol, Early Online: 1–12 ! 2014 Informa Healthcare USA, Inc. DOI: 10.3109/07388551.2014.961402 REVIEW ARTICLE Effects of bacterial communities on biofuel-producing microalgae: stimulation, inhibition and harvesting Hui Wang 1,2,3 , Russell T. Hill 2 , Tianling Zheng 3 , Xiaoke Hu 1 , and Bin Wang 1 1 Key Laboratory of Coastal Biology and Bioresource Utilization, Yantai Institute of Costal Zone Research, Chinese Academy of Sciences, Yantai, China, 2 Institute of Marine and Environmental Technology, University of Maryland Center for Environmental Science, Baltimore, MD, USA and 3 State Key Laboratory of Marine Environmental Sciences and Key Laboratory of the Ministry of Education for Coast and Wetland Ecosystem, School of Life Sciences, Xiamen University, Xiamen, China Abstract Despite the great interest in microalgae as a potential source of biofuel to substitute for fossil fuels, little information is available on the effects of bacterial symbionts in mass algal cultivation systems. The bacterial communities associated with microalgae are a crucial factor in the process of microalgal biomass and lipid production and may stimulate or inhibit growth of biofuel-producing microalgae. In addition, we discuss here the potential use of bacteria to harvest biofuel-producing microalgae. We propose that aggregation of microalgae by bacteria to achieve 4 90% reductions in volume followed by centrifugation could be an economic approach for harvesting of biofuel-producing microalgae. Our aims in this review are to promote understanding of the effects of bacterial communities on microalgae and draw attention to the importance of this topic in the microalgal biofuel field. Keywords Aggregation, algicidal, diversity, large-scale, lipid, nutrient, phycosphere, symbionts History Received 10 February 2014 Revised 17 July 2014 Accepted 23 July 2014 Published online 26 September 2014 Introduction Considering the shrinking reserves and high price of oil and especially the environmental impact of carbon dioxide emissions, traditional fossil fuels will not be a viable transportation choice for fuels in the near future. Biofuels, derived from photosynthetic organisms, that can fix solar energy must be considered as potential alternatives to fossil fuels and have the important advantages of being renewable and environmentally benign. First and second generation biofuels are already in worldwide commercial use. These biofuels are derived from vascular plants, mainly food crops that have also been chosen as energy sources. For example, bioethanol fermented from sugarcane and other sugar- producing crops has been widely used in Brazil and, to a lesser extent, in the USA (Chiaramonti, 2007), while biodiesel made from vegetable oils, as well as animal fats, is widely used in Europe (Ko ¨rbitz, 1999). Considerable disadvantages have been acknowledged for these energy sources, such as competing for arable land, increasing food prices and enhancing demand for fresh water and nitrate fertilizers. It is estimated that even if all arable lands were used to grow current oil-producing crops, less than half of the energy demand today would be met (Schenk et al., 2008). However, third generation biofuels from microalgae are considered as one of the most attractive feedstocks for high energy transportation fuels (Angermayr et al., 2009; Beer et al., 2009; Li et al., 2008a). Microalgae are prokaryotic or eukaryotic photosynthetic microorganisms that can grow rapidly and live in harsh conditions due to their unicellular or simple multicellular structure (Mata et al., 2010). Since they are rich in fatty acids, microalgae have drawn attention for their possible application for third generation biofuel production. Here, we focus on one of the neglected critical factors to be considered if successful commercial microalgal production of biofuels is to be achieved, namely, the bacterial communities associated with biofuel-producing microalgae. We synthesize recent research advances on the effects of bacterial commu- nities on microalgae, in particular the stimulation or inhib- ition of microalgal growth. Also, we emphasize a potential way to harvest biofuel-producing microalgae by the use of bacterial aggregation of the microalgae. Biofuels from microalgae Biofuels from microalgae have many advantages over biodiesel from oleaginous vascular plants and bioethanol, and seem to be the only realistic substitute for petroleum- based fuels because of several inherent advantages (Chisti, 2008). First, microalgae convert solar energy into biofuels as do other biofuel-producing plants, but the biomass and oil productivity of microalgae greatly exceeds that of vascular plants under suitable culture conditions (Chen et al., 2011; Chisti, 2010). Average biodiesel production yields from microalgae can be 10–20 times higher than the yield obtained Address for correspondence: Hui Wang, Yantai Institute of Costal Zone Research, Chinese Academy of Sciences, Yantai 264003, China. Tel: +86-535-2109150. E-mail: hwang@yic.ac.cn Critical Reviews in Biotechnology Downloaded from informahealthcare.com by Yantai Institute of Coastal Research for Sustainable Development CAS on 10/07/14 For personal use only.