Stakelama marina sp. nov., isolated from seawater of the Tangyin hydrothermal field in the Okinawa Trough.

A Gram-stain-negative, strictly aerobic, rod-shaped and non-flagellated marine bacterium, designated strain LXI357T, was isolated from deep-sea water sampled at the Tangyin hydrothermal field in the Okinawa Trough. The growth temperature range was 20-45 °C (optimum, 28 °C). Strain LXI357T was also able to grow at pH 5.0-7.5 (optimum, pH 6.0-7.0) and in the presence of 0.5-11 % (optimum, 7%, w/v) NaCl. Strain LXI357T was oxidase-negative and catalase-positive. The predominant fatty acids were C18 : 1 ω7c and C16 : 0. The major polar lipids of strain LXI357T contained phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, phospholipid, sphingoglycolipid, diphosphatidylglycero and an unidentified aminolipid. Based on the results of 16S rRNA gene sequence analysis, strain LXI357T belonged to the genus Stakelama and was most closely related to Stakelama flava CBK3Z-3T (96.28%, 16S rRNA gene sequence similarity), followed by Stakelama algicida Yeonmyeong 1-13T (95.67%), Stakelama pacifica JLT832T (95.46%) and Sphingosinicella vermicomposti YC7378T (95.43%). Genome relatedness between strain LXI357T and Stakelama flava CBK3Z-3T was computed using average nucleotide identity, digital DNA-DNA hybridization and average amino acid identity, with values of 76.02, 20.9 and 71.1 %, respectively. The genomic DNA G+C content of strain LXI357T is 64.1 mol%. In addition, strain LXI357T has multiple genes related to sulphur metabolism, including genes encoding for the Sox system. The morphological, physiological, chemotaxonomic and phylogenetic analyses clearly distinguished strain LXI357T from its closest phylogenetic neighbours. According to the results of polyphasic analyses, strain LXI357T is considered to represent a novel species of the genus Stakelama, for which the name Stakelama marina sp. nov. is proposed. The type strain is LXI357T (=MCCC 1K06076T=KCTC 82726T).

4F-Indole Enhances the Susceptibility of Pseudomonas aeruginosa to Aminoglycoside Antibiotics.

Infections caused by multidrug-resistant bacteria are becoming increasingly serious. The aminoglycoside antibiotics have been widely used to treat severe Gram-negative bacterial infections. Here, we reported that a class of small molecules, namely, halogenated indoles, can resensitize Pseudomonas aeruginosa PAO1 to aminoglycoside antibiotics such as gentamicin, kanamycin, tobramycin, amikacin, neomycin, ribosomalin sulfate, and cisomicin. We selected 4F-indole as a representative of halogenated indoles to investigate its mechanism and found that the two-component system (TCS) PmrA/PmrB inhibited the expression of multidrug efflux pump MexXY-OprM, allowing kanamycin to act intracellularly. Moreover, 4F-indole inhibited the biosynthesis of several virulence factors, such as pyocyanin, type III secretion system (T3SS), and type VI secretion system (T6SS) exported effectors, and reduced the swimming and twitching motility by suppressing the expression of flagella and type IV pili. This study suggests that the combination of 4F-indole and kanamycin can be more effective against P. aeruginosa PAO1 and affect its multiple physiological activities, providing a novel insight into the reactivation of aminoglycoside antibiotics. IMPORTANCE Infections caused by Pseudomonas aeruginosa have become a major public health crisis. Its resistance to existing antibiotics causes clinical infections that are hard to cure. In this study, we found that halogenated indoles in combination with aminoglycoside antibiotics could be more effective than antibiotics alone against P. aeruginosa PAO1 and preliminarily revealed the mechanism of the 4F-indole-induced regulatory effect. Moreover, the regulatory effect of 4F-indole on different physiological behaviors of P. aeruginosa PAO1 was analyzed by combined transcriptomics and metabolomics. We explain that 4F-indole has potential as a novel antibiotic adjuvant, thus slowing down the further development of bacterial resistance.

Biofilm formation and inhibition mediated by bacterial quorum sensing.

As a complex microbial aggregate, biofilm is a group behavior of bacterial ability to adapt to the environment. Bacteria produce biofilm substrates that enhance their tolerance to stress and cause microbial infections. Biofilm infection is usually closely related to virulence, pathogenicity, and even life-threatening to immunocompromised patients. Therefore, studying bacterial biofilm generation and regulatory mechanisms has become one of the most important fields. It is well known that biofilm formation involves group behavior and relies on complex regulation of quorum sensing (QS). A series of small molecule compounds such as indole, AI-2 (autoinducer-2), AHL (N-acyl-homoserine lactone), AIP (auto-inducing peptide), and DSF (diffusible signal factor) are widely available intraspecific or interspecific signaling molecules, with regulatory functions on a wide range of physiological activities of bacteria, including biofilm formation. Given that various bacteria employ QS mechanisms to regulate biofilm formation, inhibition of QS becomes a promising potential strategy for the treatment of bacterial infections. Here, we describe how bacterial intraspecific and interspecific signaling molecules regulate the mechanism of biofilm formation and dispersion. This may contribute to anti-biofilm active molecules and provide ideas or directions for studies on controlling bacterial infections by inhibiting biofilm formation through QS. KEY POINTS: • The formation and hazard of biofilm have been discussed. • The effects of quorum sensing on biofilm formation have been highlighted. • The inhibition of biofilm through quorum sensing has been discussed and highlighted.

Developing a new treatment for superficial fungal infection using antifungal Collagen-HSAF dressing.

Fungal pathogens are common causes of superficial clinical infection. Their increasing drug resistance gradually makes existing antifungal drugs ineffective. Heat stable antifungal factor (HSAF) is a novel antifungal natural product with a unique structure. However, the application of HSAF has been hampered by very low yield in the current microbial producers and from extremely poor solubility in water and common solvents. In this study, we developed an effective mode of treatment applying HSAF to superficial fungal infections. The marine-derived Lysobacter enzymogenes YC36 contains the HSAF biosynthetic gene cluster, which we activated by the interspecific signaling molecule indole. An efficient extraction strategy was used to significantly improve the purity to 95.3%. Scanning electron microscopy images revealed that the Type I collagen-based HSAF (Col-HSAF) has a transparent appearance and good physical properties, and the in vitro sustained-release effect of HSAF was maintained for more than 2 weeks. The effective therapeutic concentration of Col-HSAF against superficial fungal infection was explored, and Col-HSAF showed good biocompatibility, lower clinical scores, mild histological changes, and antifungal capabilities in animals with Aspergillus fumigatus keratitis and cutaneous candidiasis. In conclusion, Col-HSAF is an antifungal reagent with significant clinical value in the treatment of superficial fungal infections.

Novel indole-mediated potassium ion import system confers a survival advantage to the Xanthomonadaceae family.

Interspecific and intraspecific communication systems of microorganisms are involved in the regulation of various stress responses in microbial communities. Although the significance of signaling molecules in the ubiquitous family Xanthomonadaceae has been reported, the role bacterial communications play and their internal mechanisms are largely unknown. Here, we use Lysobacter enzymogenes, a member of Xanthomonadaceae, to identify a novel potassium ion import system, LeKdpXFABC. This import system participates in the indole-mediated interspecies signaling pathway and matters in environmental adaptation. Compared with the previously reported kdpFABC of Escherichia coli, LekdpXFABC contains a novel indispensable gene LekdpX and is directly regulated by the indole-related two-component system QseC/B. QseC autophosphorylation is involved in this process. The operon LekdpXFABC widely exists in Xanthomonadaceae. Moreover, indole promotes antimicrobial product production at the early exponential phase. Further analyses show that indole enhances potassium ion adsorption on the cell surface by upregulating the production of O-antigenic polysaccharides. Finally, we confirm that LeKdpXFABC mediation by indole is subject to the intraspecific signaling molecules DSFs, of which the biosynthesis genes always exist together with LekdpXFABC. Therefore, as a new idea, the signal collaborative strategy of indole and DSFs might ensure the persistent fitness advantage of Xanthomonadaceae in variable environments.