In response to environmental changes, Anabaena cylindrica differentiate three cell types: vegetative cells for photosynthesis, heterocysts for nitrogen fixation, and akinetes for stress survival. Cell-surface polysaccharides play important roles in cyanobacterial ecophysiology. In this study, specific cell-surface sugars were discovered in heterocysts, akinetes and vegetative cells of A. cylindrica using 20 fluorescein-labeled lectins. Both N-acetylglucosamine-binding lectins WGA and succinylated WGA bound specifically to the vegetative cells. Akinetes bound to three mannose-binding lectins (LCA, PSA, and ConA), and one of the galactose-binding lectins (GSL-I). Heterocyst also bound to ConA. However, the heterocysts in all4388 mutant of Anabaena sp. PCC 7120, in which the putative polysaccharide export protein gene all4388 was disrupted, exhibited diminished binding to ConA. Identification of distinct cell-surface sugar helped us to understand the role of polysaccharide for each cell type. Fluorescence-activated cell sorting may be applicable in isolating each cell type for comparative "omics" studies among the three cell types.

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The fern Dicranopteris dichotoma is an important pioneer species of the understory in Masson pine (Pinus massoniana) forests growing on acidic soils in the subtropical and tropical China. To improve our understanding of the role of D. dichotoma in nitrogen (N) uptake of these forests, a short-term 15N experiment was conducted at mountain ridge (MR, with low N level) and mountain foot (MF, with high N level). We injected 15N tracers as 15NH4, 15NO3 or 15N-glycine into the soil surrounding each plant at both MR and MF sites. Three hours after tracer injection, the fern D. dichotoma took up 15NH4 + significantly faster at MF than at MR, but it showed significantly slower uptake of 15NO3 − at MF than at MR. Consequently, 15NO3 − made greater contribution to the total N uptake (50% to the total N uptake) at MR than at MF, but 15N-glycine only contributed around 11% at both sites. Twenty-four hours after tracer injection, D. dichotoma preferred 15NH4 + (63%) at MR, whereas it preferred 15NO3 − (47%) at MF. We concluded that the D. dichotoma responds distinctly in its uptake pattern for three available N species over temporal and spatial scales, but mainly relies on inorganic N species in the subtropical forest. This suggests that the fern employs different strategies to acquire available N which depends on N levels and time.

1Some vegetative cells of Anabaena cylindrica are programed to differentiate semi-regularly spaced, 2 single heterocysts along filaments. Since heterocysts are terminally differentiated non-dividing 3 cells, with the sole known function for solar-powered N2-fixation, is it necessary for a heterocyst 4 to retain the entire genome (7.1 Mbp) from its progenitor vegetative cell? By sequencing the 5 heterocyst genome, we discovered and confirmed that at least six DNA elements (0.12 Mbp) are 6 deleted during heterocyst development. The six-element deletions led to the restoration of five 7 genes (nifH1, nifD, hupL, primase P4 and a hypothetical protein gene) that were interrupted in 8 vegetative cells. The deleted elements contained 172 genes present in the genome of vegetative 9 cells. By sequence alignments of intact nif genes (nifH, nifD and hupL) from N2-fixing 10 cyanobacteria (multicellular and unicellular) as well as other N2-fixing bacteria (non-11 cyanobacteria), we found that interrupted nif genes all contain the conserved core sequences that 12 may be required for phage DNA insertion. Here, we discuss the nif genes interruption which 13 uniquely occurs in heterocyst-forming cyanobacteria. To our best knowledge, this is first time to 14 sequence the genome of heterocyst, a specially differentiated oxic N2-fixing cell. This research 15 demonstrated that (1) different genomes may occur in distinct cell types in a multicellular 16 bacterium; and (2) genome editing is coupled to cellular differentiation and/or cellular function in 17 a heterocyst-forming cyanobacterium. 18 19 Keywords 20 cyanobacteria, heterocysts, oxic nitrogen fixation, genome editing, phage DNA insertion, 21 multicellular bacterium 22 Bioinformatics analysis. Reads trimming, assembly and mapping were carried out using CLC 132 Genomics Workbench 10.1.1 (Qiagen). Trimming was carried out using a Q of 20 as the cutoff, 133 eliminating any read with any ambiguous nucleotide and removing the 5 and 15 terminal 134 nucleotides in the 3' and 5' ends respectively. Assembly of the trimmed reads was accomplished 135 by setting an arbitrary minimum contig length of 3,000 bp and using the automated function to 136 select a word size of 23 and a bubble size of 50; finally, reads were mapped (mismatch cost: 2, 137 insertion cost: 3, deletion cost: 3, minimum length fraction: 0.5 and minimum similarity fraction: