This study presents the complete nucleotide sequence of Anabaena sp. ATCC 33047 (Anabaena CA), a filamentous, nitrogen-fixing marine cyanobacterium, which under salt stress conditions accumulates sucrose internally. The elucidation of the genome will contribute to the understanding of cyanobacterial diversity.

The objective of this paper is to describe the use of membranes for energy efficient biomass harvesting and dewatering. The dewatering of Nannochloropsis sp. was evaluated with polymeric hollow fiber and tubular inorganic membranes to demonstrate the capabilities of a membrane-based system to achieve microalgal biomass of >150 g/L (dry wt.) and ∼99% volume reduction through dewatering. The particle free filtrate containing the growth media is suitable for recycle and reuse. For cost-effective processing, hollow fiber membranes can be utilized to recover 90-95% media for recycle. Tubular membranes can provide additional media and water recovery to achieve target final concentrations. Based on the operating conditions used in this study and taking into scale-up considerations, an integrated hollow fiber-tubular membrane system can process microalgal biomass with at least 80% lower energy requirement compared to traditional processes. Backpulsing was found to be an effective flux maintenance strategy to minimize flux decline at high biomass concentration. An effective chemical cleaning protocol was developed for regeneration of fouled membranes.

Biodegradation is increasingly being considered as a less expensive alternative to physical and chemical means of decomposing organic pollutants. Pathways of biodegradation have been characterized for a number of heterotrophic microorganisms, mostly soil isolates, some of which have been used for remediation of water. Because cyanobacteria are photoautotrophic and some can fix atmospheric nitrogen, their use for bioremediation of surface waters would circumvent the need to supply biodegradative heterotrophs with organic nutrients. This paper demonstrates that two filamentous cyanobacteria have a natural ability to degrade a highly chlorinated aliphatic pesticide, lindane (␥-hexachlorocyclohexane); presents quantitative evidence that this ability can be enhanced by genetic engineering; and provides qualitative evidence that those two strains can be genetically engineered to degrade another chlorinated pollutant, 4-chlorobenzoate.

Nitrate is essential for lindane dechlorination by the cyanobacteria Anabaena sp. strain PCC7120 and Nostoc ellipsosporum, as it is for dechlorination of other organic compounds by heterotrophic microorganisms. Based on analyses of mutants and effects of environmental factors, we conclude that lindane dechlorination by Anabaena sp. requires a functional nir operon that encodes the enzymes for nitrate utilization.Cyanobacteria are photoautotrophic microorganisms common to a variety of environments including polluted ones. Earlier, we reported that two filamentous nitrogen-fixing cyanobacteria, Anabaena sp. strain PCC7120 and Nostoc ellipsosporum transformed lindane (14) first to ␥-pentachlorocyclohexene and then to a mixture of chlorobenzenes (Fig. 1). This process was cometabolic and depended on the presence of nitrate (14).Nitrate-dependent dehalogenation of organic compounds by different heterotrophic bacteria has been described in the past (1, 9, 21), but no mechanism for this process or link to genetic systems has been proposed. For some microorganisms dehalogenation was coupled with denitrification (9). In both cyanobacteria and anaerobic denitrifying microorganisms, nitrate uptake and reduction are initial processes of nitrate utilization, and the genes for these processes are organized in similar operons (4,17,19,24,26). At the level of nitrite reduction, metabolic pathways diverge and lead to the assimilatory chain for cyanobacteria (8), algae (3), fungi (12), and plants (27) and the dissimilatory chain for heterotrophic anaerobic microorganisms (28). In Anabaena sp. strain PCC7120, genes organized in an operon as 5Ј-nirA-nrtABCD-narB-3Ј encode nitrite reductase, nitrate transport proteins, and nitrate reductase (2, 7), similar to other cyanobacteria (17, 23).We report that Anabaena sp. nirA, nrtC, nrtD, or narB mutants cannot dechlorinate lindane in the presence of nitrate. Dechlorination is also inhibited in the dark and in the presence of ammonium, both of which are environmental inhibitors of the function(s) encoded by the nir operon. Fifteen strains of wild-type cyanobacteria screened by us degraded lindane.Effect of mutations in the nir operon on lindane dechlorination by an Anabaena sp. We analyzed lindane degradation by Anabaena sp. transpositional mutants TLN10 (insertion in the nirA gene), TLN12 (insertion in the nrtC gene), TLN21 (insertion at the 3Ј end of the nrtD gene), and DR796 (site-directed interposition in the narB gene), which have been described in detail by Cai and Wolk (2). Growth of the cultures at 28°C was monitored by measuring chlorophyll content. Experimental procedures were as described by Kuritz and Wolk (14). Addition of lindane to the cultures to a final concentration of 0.5 mg/liter allowed us to monitor the kinetics of the disappearance of lindane associated with the cells. To measure concentrations of cell-associated lindane, 2 ml of each culture was sampled, washed twice with 2 ml of sterile water, resuspended in 1 ml of sterile water, subjected to sonication in an ice...

The clones generated in a sequencing project represent a resource for subsequent analysis of the organism whose genome has been sequenced. We describe an interrelated group of cloning vectors that either integrate into the genome or replicate, and that enhance the utility, for developmental and other studies, of the clones used to determine the genomic sequence of the cyanobacterium, Anabaena sp. strain PCC 7120. One integrating vector is a mobilizable BAC vector that was used both to generate bridging clones and to complement transposon mutations. Upon addition of a cassette that permits mobilization and selection, pUC-based sequencing clones can also integrate into the genome and thereupon complement transposon mutations. The replicating vectors are based on cyanobacterial plasmid pDU1, whose sequence we report, and on broad-host-range plasmid RSF1010. The RSF1010- and pDU1-based vectors provide the opportunity to express different genes from either cell-type-specific or -generalist promoters, simultaneously from different plasmids in the same cyanobacterial cells. We show that pDU1 ORF4 and its upstream region play an essential role in the replication and copy number of pDU1, and that ORFs alr2887 and alr3546 (hetF A) of Anabaena sp. are required specifically for fixation of dinitrogen under oxic conditions.