Exopolysaccharides Play a Role in the Swarming of the Benthic Bacterium Pseudoalteromonas sp. SM9913.

Most marine bacteria secrete exopolysaccharide (EPS), which is important for bacterial survival in the marine environment. However, it is still unclear whether the self-secreted EPS is involved in marine bacterial motility. Here we studied the role of EPS in the lateral flagella-driven swarming motility of benthic bacterium Pseudoalteromonas sp. SM9913 (SM9913) by a comparison of wild SM9913 and ΔepsT, an EPS synthesis defective mutant. Reduction of EPS production in ΔepsT did not affect the growth rate or the swimming motility, but significantly decreased the swarming motility on a swarming plate, suggesting that the EPS may play a role in SM9913 swarming. However, the expression and assembly of lateral flagella in ΔepsT were not affected. Instead, ΔepsT had a different swarming behavior from wild SM9913. The swarming of ΔepsT did not have an obvious rapid swarming period, and its rate became much lower than that of wild SM9913 after 35 h incubation. An addition of surfactin or SM9913 EPS on the surface of the swarming plate could rescue the swarming level. These results indicate that the self-secreted EPS is required for the swarming of SM9913. This study widens our understanding of the function of the EPS of benthic bacteria.

Physiological and genetic analyses reveal a mechanistic insight into the multifaceted lifestyles of Pseudoalteromonas sp. SM9913 adapted to the deep-sea sediment.

Although bacteriobenthos play a major role in the degradation of particulate organic matter in marine sediment, knowledge of the sediment-adapted lifestyles of bacteriobenthos is still scarce. Here, the particle-associated, swimming and swarming lifestyles of the benthonic bacterium Pseudoalteromonas sp. SM9913 (SM9913) were illustrated. SM9913 had a clay particle-associated lifestyle, and its exopolysaccharide played an important role in this lifestyle. SM9913 also had swimming and swarming motilities, indicating that it may have swimming and swarming lifestyles in the sediment. The lateral flagella were responsible for the swarming motility, and the polar flagella were responsible for the swimming motility. Iron limitation was an indispensable inductive signal of the swarming motility. An analysis of the motilities of SM9913 and its mutants in clay demonstrated that SM9913 moved in clay by both swimming and swarming motilities. Genomic analysis suggests that having two flagella systems is most likely a common adaptation of some bacteriobenthos to the sediment environment. Our results reveal the lifestyles of benthonic SM9913, providing a better understanding of the environmental adaptation of benthonic bacteria.

Development of a genetic system for the deep-sea psychrophilic bacterium Pseudoalteromonas sp. SM9913.

BACKGROUND: Pseudoalteromonas species are a group of marine gammaproteobacteria frequently found in deep-sea sediments, which may play important roles in deep-sea sediment ecosystem. Although genome sequence analysis of Pseudoalteromonas has revealed some specific features associated with adaptation to the extreme deep-sea environment, it is still difficult to study how Pseudoalteromonas adapt to the deep-sea environment due to the lack of a genetic manipulation system. The aim of this study is to develop a genetic system in the deep-sea sedimentary bacterium Pseudoalteromonas sp. SM9913, making it possible to perform gene mutation by homologous recombination. RESULTS: The sensitivity of Pseudoalteromonas sp. SM9913 to antibiotic was investigated and the erythromycin resistance gene was chosen as the selective marker. A shuttle vector pOriT-4Em was constructed and transferred into Pseudoalteromonas sp. SM9913 through intergeneric conjugation with an efficiency of 1.8 × 10-3, which is high enough to perform the gene knockout assay. A suicide vector pMT was constructed using pOriT-4Em as the bone vector and sacB gene as the counterselective marker. The epsT gene encoding the UDP-glucose lipid carrier transferase was selected as the target gene for inactivation by in-frame deletion. The epsT was in-frame deleted using a two-step integration-segregation strategy after transferring the suicide vector pMT into Pseudoalteromonas sp. SM9913. The ΔepsT mutant showed approximately 73% decrease in the yield of exopolysaccharides, indicating that epsT is an important gene involved in the EPS production of SM9913. CONCLUSIONS: A conjugal transfer system was constructed in Pseudoalteromonas sp. SM9913 with a wide temperature range for selection and a high transfer efficiency, which will lay the foundation of genetic manipulation in this strain. The epsT gene of SM9913 was successfully deleted with no selective marker left in the chromosome of the host, which thus make it possible to knock out other genes in the same host. The construction of a gene knockout system for Pseudoalteromonas sp. SM9913 will contribute to the understanding of the molecular mechanism of how Pseudoalteromonas adapt to the deep-sea environment.

Glaciecola arctica sp. nov., isolated from Arctic marine sediment.

A Gram-negative, motile, psychrotolerant, oxidase- and catalase-positive bacterium, designated BSs20135(T), was isolated from Arctic marine sediment. Cells were straight or slightly curved rods and formed circular, convex and yellowish-brown colonies. Buds and prosthecae could be produced. The strain grew at 4-28 °C (optimum 25 °C) and with 1-5 % (w/v) NaCl (optimum 2 %) and hydrolysed aesculin and DNA, but did not reduce nitrate to nitrite. Phylogenetic analysis of 16S rRNA gene sequences indicated that strain BSs20135(T) belonged to the genus Glaciecola and shared 93.6-97.7 % sequence similarity with the type strains of known species of the genus Glaciecola. The major cellular fatty acids of strain BSs20135(T) were summed feature 3 (comprising C(16 : 1)ω7c and/or iso-C(15 : 0) 2-OH), C(16 : 0), C(17 : 1)ω8c and C(18 : 1)ω7c. The genomic DNA G+C content was 40.3 mol%. Based on 16S rRNA gene sequence analysis, DNA-DNA hybridization data and phenotypic and chemotaxonomic characterization, strain BSs20135(T) represents a novel species, for which the name Glaciecola arctica sp. nov. is proposed. The type strain is BSs20135(T) ( = CCTCC AB 209161(T)  = KACC 14537(T)).