Involvement of luxS in Biofilm Formation by Capnocytophaga ochracea

Illuminating the oral microbiome and its host interactions: tools and approaches for molecular microbiology studies

Advancements in DNA sequencing technologies within the last decade have stimulated an unprecedented interest in the human microbiome, largely due the broad diversity of human diseases found to correlate with microbiome dysbiosis. As a direct consequence of these studies, a vast number of understudied and uncharacterized microbes have been identified as potential drivers of mucosal health and disease. The looming challenge in the field is to transition these observations into defined molecular mechanistic studies of symbiosis and dysbiosis. In order to meet this challenge, many of these newly identified microbes will need to be adapted for use in experimental models. Consequently, this review presents a comprehensive overview of the molecular microbiology tools and techniques that have played crucial roles in genetic studies of the bacteria found within the human oral microbiota. Here, we will use specific examples from the oral microbiome literature to illustrate the biology supporting these techniques, why they are needed in the field, and how such technologies have been implemented. It is hoped that this information can serve as a useful reference guide to help catalyze molecular microbiology studies of the many new understudied and uncharacterized species identified at different mucosal sites in the body.

Characterization of CoCas9 nuclease from Capnocytophaga ochracea

Cas9 nucleases are widely used for genome editing and engineering. Cas9 enzymes encoded by CRISPR-Cas defence systems of various prokaryotic organisms possess different properties such as target site preferences, size, and DNA cleavage efficiency. Here, we biochemically characterized CoCas9 from Capnocytophaga ochracea, a bacterium that inhabits the oral cavity of humans and contributes to plaque formation on teeth. CoCas9 recognizes a novel 5'-NRRWC-3' PAM and efficiently cleaves DNA in vitro. Functional characterization of CoCas9 opens ways for genetic engineering of C. ochracea using its endogenous CRISPR-Cas system. The novel PAM requirement makes CoCas9 potentially useful in genome editing applications.

OxyR inactivation reduces the growth rate and oxidative stress defense in Capnocytophaga ochracea

OBJECTIVE

The human oral cavity harbors several bacteria. Among them, Capnocytophaga ochracea, a facultative anaerobe, is responsible for the early phase of dental plaque formation. In this phase, the tooth surface or tissue is exposed to various oxidative stresses. For colonization in the dental plaque phase, a response by hydrogen peroxide (H₂O₂)-sensing transcriptional regulators, such as OxyR, may be necessary. However, to date, no study has elucidated the role of OxyR protein in C. ochracea.

METHODS

Insertional mutagenesis was used to create an oxyR mutant, and gene expression was evaluated by reverse transcription-polymerase chain reaction and quantitative real-time reverse transcription-polymerase chain reaction. Bacterial growth curves were generated by turbidity measurement, and the sensitivity of the oxyR mutant to H₂O₂ was assessed using the disc diffusion assay. Finally, a two-compartment system was used to assess biofilm formation.

RESULTS

The oxyR mutant grew slower than the wild-type under anaerobic conditions. The agar diffusion assay revealed that the oxyR mutant had increased sensitivity to H₂O₂. The transcript levels of oxidative stress defense genes, sod, ahpC, and trx, were lower in the oxyR mutant than in the wild-type strain. The turbidity of C. ochracea, simultaneously co-cultured with Streptococcus gordonii, was lower than that observed under conditions of homotypic growth. Moreover, the percentage decrease in growth of the oxyR mutant was significantly higher than that of the wild-type.

CONCLUSIONS

These results show that OxyR in C. ochracea regulates adequate in vitro growth and escapes oxidative stress.

Catheter-related bloodstream infection due to biofilm-producing Capnocytophaga sputigena

•

Capnocytophaga sputigena is a rare pathogen with diverse clinical presentations.

•

We report a case of catheter-related C. sputigena bloodstream infection.

•

C. sputigena clinical isolates can form biofilms in vitro.

•

Biofilm development by Capnocytophaga species may potentiate disease pathogenesis.

Capnocytophaga sputigena is a facultatively-anaerobic bacterium that is part of the human oropharyngeal microflora. Although C. sputigena bacteremia is uncommon, systemic infections have been reported in both immunocompetent and immunocompromised patients. We report a case of catheter-related bloodstream infection by C. sputigena and highlight its enhanced biofilm-forming capacity in vitro.

Role of Hyalin-like Protein in Gliding and Biofilm Formation by Capnocytophaga Ochracea

Capnocytophaga ochracea possesses a type-IX secretion system that exports proteins which have a gliding motility-associated C-terminal (CTD) domain. This system is found in several species of the Bacteroidetes phylum. Hyalin, a large protein encoded by Coch_0033 in C. ochracea ATCC 27872, has a CTD domain and is posited to be involved in quorum sensing according to the database of the Kyoto Encyclopedia of Genes and Genomes. This suggests that it plays a role in biofilm formation via interbacterial communication. The aim of this study was to investigate the potential role of the hyalin-like protein coded by the Coch_0033 gene in gliding and biofilm formation of C. ochracea. A hyalin-like protein-deficient mutant strain of C. ochracea, designated mutant WR-1, was constructed through insertion of the ermF-ermAM cassette into the target gene. The spreading feature at the edge of the colony was lost in the mutant strain. Crystal violet and confocal laser scanning microscopy revealed no difference between the quantity of biofilm organized by the mutant and that organized by the wild-type strain. These data suggest that the hyalin-like protein encoded by the Coch_0033 gene is indeed involved in C. ochracea gliding activity.

The impact of Paenibacillus polymyxa HY96-2 luxS on biofilm formation and control of tomato bacterial wilt

The focus of this study was to investigate the effects of luxS, a key regulatory gene of the autoinducer-2 (AI-2) quorum sensing (QS) system, on the biofilm formation and biocontrol efficacy against Ralstonia solanacearum by Paenibacillus polymyxa HY96-2. luxS mutants were constructed and assayed for biofilm formation of the wild-type (WT) strain and luxS mutants of P. polymyxa HY96-2 in vitro and in vivo. The results showed that luxS positively regulated the biofilm formation of HY96-2. Greenhouse experiments of tomato bacterial wilt found that from the early stage to late stage postinoculation, the biocontrol efficacy of the luxS deletion strain was the lowest with 50.70 ± 1.39% in the late stage. However, the luxS overexpression strain had the highest biocontrol efficacy with 75.66 ± 1.94% in the late stage. The complementation of luxS could restore the biocontrol efficacy of the luxS deletion strain with 69.84 ± 1.09% in the late stage, which was higher than that of the WT strain with 65.94 ± 2.73%. Therefore, we deduced that luxS could promote the biofilm formation of P. polymyxa HY96-2 and further promoted its biocontrol efficacy against R. solanacearum.

Members of the Oral Microbiota Are Associated with IL-8 Release by Gingival Epithelial Cells in Healthy Individuals

The triggers for the onset of oral diseases are still poorly understood. The aim of this study was to characterize the oral bacterial community in healthy humans and its association with nutrition, oral hygiene habits, and the release of the inflammatory marker IL-8 from gingival epithelial cells (GECs) with and without stimulation by bacterial endotoxins to identify possible indicator operational taxonomic units (OTUs) associated with inflammatory marker status. GECs from 21 healthy participants (13 females, 8 males) were incubated with or without addition of bacterial lipopolysaccharides (LPSs), and the oral microbiota was profiled using 16S rRNA gene-targeted sequencing. The basal IL-8 release after 6 h was between 9.9 and 98.2 pg/ml, and bacterial communities were characteristic for healthy oral microbiota. The composition of the oral microbiota was associated with basal IL-8 levels, the intake of meat, tea, white wine, sweets and the use of chewing gum, as well as flossing habits, allergies, gender and body mass index. Additionally, eight OTUs were associated with high basal levels of IL-8 and GEC response to LPS, with high basal levels of IL-8, and 1 with low basal levels of IL8. The identification of indicator bacteria in healthy subjects with high levels of IL-8 release is of importance as they may be promising early warning indicators for the possible onset of oral diseases.