Extracellular polysaccharide synthesis in a bloom-forming strain of Microcystis aeruginosa: implications for colonization and buoyancy

Abstract

Microcystis, the dominant species among cyanobacterial blooms, normally forms colonies under natural conditions but exists as single cells or paired cells in axenic laboratory cultures after long-term cultivation. Here, a bloom-forming Microcystis aeruginosa strain CHAOHU 1326 was studied because it presents a colonial morphology and grows on the water surface during axenic laboratory culturing. We first examined the morphological features of strain CHAOHU 1326 and three other unicellular M. aeruginosa strains FACHB-925, FACHB-940, and FACHB-975 cultured under the same conditions by scanning and transmission electron microscopy. Then, we compared the extracellular polysaccharide (EPS)-producing ability of colonial strain CHAOHU 1326 to that of the three unicellular M. aeruginosa strains, and found that strain CHAOHU 1326 produced a higher amount of EPS than the other strains during growth. Moreover, based on genome sequencing, multiple gene clusters implicated in EPS biosynthesis and a cluster of 12 genes predicted to be involved in gas vesicle synthesis in strain CHAOHU 1326 were detected. These predicted genes were all functional and expressed in M. aeruginosa CHAOHU 1326 as determined by reverse transcription PCR. These findings provide a physiological and genetic basis to better understand colony formation and buoyancy control during M. aeruginosa blooming.

Comparative genomics analysis of c-di-GMP metabolism and regulation in Microcystis aeruginosa

“…As shown in Table 1, except for strains NIES 2481 [39] and NIES 2549 [40], no plasmid sequence was discovered in other strains. Among them, genome sequences of the strains CHAOHU 1326 and NaRes975 were recently released by our laboratory [41,42], and their general information are shown in Table S1. The average size of the genomes was 4.97 ± 0.40 Mb, and the average G + C content was 42.66 ± 0.26%.…”

“…The genome features of these selected strains were listed in Table 1. The sequencing and sequence assembly of M. aeruginosa strain NaRes975 and CHAOHU 1326 genomes were performed as previously described [41].…”

Comparative genomics analysis of c-di-GMP metabolism and regulation in Microcystis aeruginosa

“…As shown in Table 1, except for strains NIES 2481 [39] and NIES 2549 [40], no plasmid sequences were discovered in other strains. Among them, genome sequences of the strains CHAOHU 1326 and NaRes975 were recently released by our laboratory [41][42], and their general information are shown in Table S1. The average size of the genomes was 4.97 0.40 Mb, and the average G+C content was 42.66 0.26%.…”

Comparative genomics analysis of c-di-GMP metabolism and regulation in Microcystis aeruginosa

“…The majority of the M. aeruginosa strains were isolated in different locations, but no correlation was found between their geographic distribution or bloom-forming ability and phylogenetic relationships (Table 1). Among them, strains CHAOHU 1326 [44], DIANCHI905, NaRes975, and TAIHU98 [45] are bloom-forming strains isolated from China. Strains NIES843 [46] and PCC7806SL are representatives of toxic (microcystin-producing) bloom-forming strains; in contrast, NIES98 [47], NIES44 [48], NIES2549 [38], and NIES87 [49] are non-microcystin-producing strains.…”

“…Draft genomes that consisted of more than 1,000 contigs were omitted to obtain consistent genome quality. The sequencing and sequence assembly of M. aeruginosa strain NaRes975 and CHAOHU 1326 genomes were performed as previously described [44].…”