Cyanobacterial akinete induction and its application as biofertilizer for rice cultivation Sasidhorn Innok & Somporn Chunleuchanon & Nantakorn Boonkerd & Neung Teaumroong Received: 25 July 2008 / Revised and accepted: 19 January 2009 / Published online: 4 March 2009 # Springer Science + Business Media B.V. 2009 Abstract Nostoc sp. VICCR1-1 was induced in order to form akinetes on the basis of nutrient modification. Phosphorus and iron were found to be the critical for akinete differentiation, especially when both elements were omitted. The number of akinete cells increased up to 20% when compared with culturing in BG11 0 medium (without N source). In addition, CaCl 2 played a role in heterocyst differentiation, and was able to induce heterocyst ranging between 30% and 46%. In order to prepare akinetes as inoculum, the dried form of akinetes was prepared by mixing it with montmorillonite clay. The inoculum with the amount of 2.8×10 6 cells m -2 was applied to rice (Oryza sativa) fields. After harvesting, the grain yields from chemical N fertilizer, vegetative cells, and akinete inoculum treatments were not significantly different. To monitor the persistence of Nostoc sp. VICCR1-1 after harvesting, the most probable number-denaturing gradient gel electropho- resis technique using 16S rRNA gene was employed. The results indicated that the remaining population is at 2.5× 10 5 and 1.62×10 6 cells m -2 in treatments supplied with vegetative cells and akinete inocula, respectively. Akinete induction might be one of the appropriate approaches for producing cyanobacterial inoculum. Keywords Nostoc sp. . Akinete induction . Akinete inoculum . Montmorillonite clay . Rice cultivation . MPN-DGGE Introduction The term “algalization” is applied to the use of a defined mixture of cyanobacterial species to inoculate soil, and research on algalization is going on in all major rice- producing countries. The averages of the results from all these studies have shown an increase in grain yield of 15– 20% in field experiments. Most commonly, a Nostoc was generally dominant among the N 2 -fixing cyanobacteria present in the inocula produced (Roger et al. 1987). Since many heterocystous cyanobacteria can undergo one or several of a variety of cellular differentiation processes that most commonly take place as adaptive responses to environmental changes, the differentiation of akinetes has evident connections to the differentiation of heterocysts because some common specific structural components have been identified in the wall of both cell types that are synthesized during the differentiation pro- cesses (Wolk et al. 1994). In some strains, the pattern of heterocyst distribution determines akinete differentiation in the absence of combined nitrogen (Sutherland et al. 1979). There is an attempt to improve the technology by developing new economically feasible protocols for the production of quality inoculum, so that these organisms can be practically exploited on a large scale. The basic changes the technology has undergone include: (a) indoor produc- tion of algal biomass under controlled conditions, (b) a suitable and cheap growth medium for faster growth of the organisms, and (c) mixing the cells with a suitable carrier material. For example, Nohr (1990) produced immobilized J Appl Phycol (2009) 21:737–744 DOI 10.1007/s10811-009-9409-x S. Innok : N. Boonkerd : N. Teaumroong (*) School of Biotechnology, Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand e-mail: neung@ccs.sut.ac.th S. Chunleuchanon Department of Soil Sciences and Conservation, Faculty of Agriculture, Chiang Mai University, Chiang Mai 50002, Thailand