| To a certain extent, bacteria cell morphogenesis is due to cell growth, cell division and cell cycle regulation. Cytoplasm synthesis and chromosome replication represent cell growth. Cell division includes cell wall and cell membrane reconstruction and septation. Cell cycle regulation involves specific gene expression, protein localization and protein phosphorylation. So far, cell division genes have been widely studied in rod-shaped bacteria, such as Bacillus subtilis and Escherichia coli. To our best knowledge, there are limited researches focused on the genetic foundation of environmental bacteria because of their richness diversity. A bacterium(signated as GY32) which was isolated from polybrominated diphenyl ether contaminated river sediment was identified. The bioremediation function of the strain was determined by deca-brominated diphenyl ether(BDE209) adsorption and transformation. The special filament-to-rod cell cycle model of strain GY32 was constructed. Genome sequencing, comparative genomic analysis and transcriptomic analysis were used to understand the molecular basis of the cell morphogenesis of the strain. And, the main results of this study as follows:Strain GY32 revealed adsorption and transformation ability of decabromodiphenyl ether(BDE209). The adsorption of BDE209 by live and heat-killed cells was 18.43 and 13.05 μg L-1, respectively. For one month biotransformation experiments, 31.7% and 56.9% of 0.6 μmol L-1(initial concentration) BDE209 was disappeared under anaerobic and facultative anaerobic conditions, and it was insignificantly transformed under aerobic condition.The physiological characteristics, biochemical characteristics and molecular feature of strain GY32 revealed it is a novel species of the genus Lysinbacillus. By comparing with its relatives, strain GY32 showed differences in cell morphology, carbon resource utilization, nitrate reduction and oxidase. The phylogenetic distance from its closest relative measured by DNA-DNA relatedness and DNA(G+C) mol % and its phenotypic properties demonstrated that strain GY32 represents a novel species of the genus Lysinibacillus, for which the name Lysinibacillus varians sp. nov. was proposed. The proposed new species is not only a supplement of Lysinibacillus but also important for subsequent researches, such as biological function and genetic basis of phenotype.Time-lapse microscopy was used to monitor spore germination, single cell elongation and division, cell growth and spore formation. A conceptual model for the lifecycle of strain GY32 was proposed. After a spore was pre-incubated at 30 ?С for 2 h, the lifecycle from a spore germination to next-generation spore-forming could be divided into seven major steps:(i) a spore expands and germinates in the first 4.5 h;(ii) the bud emerges from the spore and becomes thicker and longer in the next 2.0 h and then the rod-shaped bud(< 10 μm)releases from the cortex and crust of the spore;(iii) the rod cell elongates to form a filament(~ 466.1 μm) in the next 1.5 h;(iv) the filamentous cell asymmetrically divided into shorter filaments. The parental cell and its progeny reproduces with a high growth rate and motile rod cells are observed after a further 3.0 h;(v) in another 5 h, filamentous cells and rod cells co-exist in the medium – some filaments which could not divide immediately undergo autolysis;(vi) rod cells(5.0 ~ 10.0 μm) become dominant in the following 12 h; and(vii) new endospores subsequently form after a further 5 h. The cell cycle of strain GY32 distict from other known rod and coccoid bacteria and the proposed model in the present study can make a contribution to reveal the mechanism of bacteria cell morphogenesis.The completion of the full genome sequence revealed the genes involved in cell morphogenesis of Lysinibacillus varians GY32. The circle chromosome contains multiple clusters of transcriptional regulator, two-component system and sigma factors, providing the organism with the ability to regulate a filament-to-rod cell cycle progression. Genes in cell division showed high similarity with orthologs in other genomes and mobile genetic elements brought in new cell wall synthesis genes. All relative genes above are foundation of its unique cell morphology and broaden our understanding of the genetic foundation of bacteria cell cycle.Comparative genomic analysis of L. varians GY32 and common rod bacteria, and comparative transcriptomic analysis of filamentous and rod cells of GY32, provides the transcription level of the cell morphogenesis related genes. There were 1300 CDS(28.6% of all identified CDS in the genome) without orthologs in other sequenced Lysinibacillus sp. genomes. They were annonated with function of transcription, signal transmission, cell wall/cell membrane/envelope forming, carbonhydrate transport and metabolism, and amino acid transport and metabolism. During filament-to-rod transition,(i) the genes fts L, div IC and ded D, which involved in division site selection were up-regulated;(ii) sep F, which anchor the Z ring to cell membrane was up-regulated;(iii) genes encoding proteins that play a role in chromosome replication and segregation were significantly increased in abundance, such as par A/soj and par B; and(iv) significantly increased abundance of cwl K, pbp2 B, maf B-like, fts E and fts X may resulted in rapid septum formation. Since the scaffold gene of cell divisome, fts Z, showed no transcription difference in filaments and rods, and chromosome could segregate in filaments, Fts Z polymer could not anchor to cell membrane was considered to be the key reason of filamentous cell.In conclusion, this study identified and proposed a novel Lysinibacillus species with special filament-to-rod cell cycle. With the annotated genome sequence, comparative genomic analysis and transcriptomic analysis, a description of the genetic foundation involved in the special cell morphogenesis of L. varians GY32 was within reach. After spore germination, divisome could not anchor to cell membrane and absent the energy for constriction, cell stretch into filament. During filament-to-rod transition, sep F up-regulated and facilitate Z ring assembly and anchoring, filaments vigorously divided into rods. The further exploration by proteome, linked to green fluorescent protein tracking and site-directed mutagenesis studies, will help us to elucidate the mechanism of the special cell cycle regulation. In addition, the the BDE209 adsorption and transformation function suggested the application prospect of strain GY32. |
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