Acinetobacter nosocomialis utilizes a unique type VI secretion system to promote its survival in niches with prey bacteria.

Pathogenic bacteria of the Acinetobacter genus pose a severe threat to human health worldwide due to their strong adaptability, tolerance, and antibiotic resistance. Most isolates of these bacteria harbor a type VI secretion system (T6SS) that allows them to outcompete co-residing microorganisms, but whether this system is involved in acquiring nutrients from preys remains less studied. In this study, we found that Ab25, a clinical isolate of Acinetobacter nosocomialis, utilizes a T6SS to kill taxonomically diverse microorganisms, including bacteria and fungi. The T6SS of Ab25 is constitutively expressed, and among the three predicted effectors, T6e1, a member of the RHS effector family, contributes the most for its antimicrobial activity. T6e1 undergoes self-cleavage, and a short carboxyl fragment with nuclease activity is sufficient to kill target cells via T6SS injection. Interestingly, strain Ab25 encodes an orphan VgrG protein, which when overexpressed blocks the firing of its T6SS. In niches such as dry plastic surfaces, the T6SS promotes prey microorganism-dependent survival of Ab25. These results reveal that A. nosocomialis employs T6SSs that are highly diverse in their regulation and effector composition to gain a competitive advantage in environments with scarce nutrient supply and competing microbes.IMPORTANCEThe type VI secretion system (T6SS) plays an important role in bacterial adaptation to environmental challenges. Members of the Acinetobacter genus, particularly A. baumannii and A. nosocomialis, are notorious for their multidrug resistance and their ability to survive in harsh environments. In contrast to A. baumannii, whose T6SS has been well-studied, few research works have focused on A. nosocomialis. In this study, we found that an A. nosocomialis strain utilizes a contitutively active T6SS to kill diverse microorganisms, including bacteria and fungi. Although T6SS structural proteins of A. nosocomialis are similar to those of A. baumannii, the effector repertoire differs greatly. Interestingly, the T6SS of the A. nosocomialis strain codes for an ophan VgrG protein, which blocks the firing of the system when overexpressed, suggesting the existence of a new regulatory mechanism for the T6SS. Importantly, although the T6SS does not provide an advantage when the bacterium is grown in nutrient-rich medium, it allows A. nosocomialis to survive better in dry surfaces that contain co-existing bacteria. Our results suggest that killing of co-residing microorganisms may increase the effectiveness of strategies designed to reduce the fitness of Acinetobacter bacteria by targeting their T6SS.

Osmolyte-producing microbial biostimulants regulate the growth of Arachis hypogaea L. under drought stress.

Globally, drought stress poses a significant threat to crop productivity. Improving the drought tolerance of crops with microbial biostimulants is a sustainable strategy to meet a growing population's demands. This research aimed to elucidate microbial biostimulants' (Plant Growth Promoting Rhizobacteria) role in alleviating drought stress in oil-seed crops. In total, 15 bacterial isolates were selected for drought tolerance and screened for plant growth-promoting (PGP) attributes like phosphate solubilization and production of indole-3-acetic acid, siderophore, hydrogen cyanide, ammonia, and exopolysaccharide. This research describes two PGPR strains: Acinetobacter calcoaceticus AC06 and Bacillus amyloliquefaciens BA01. The present study demonstrated that these strains (AC06 and BA01) produced abundant osmolytes under osmotic stress, including proline (2.21 and 1.75 µg ml- 1), salicylic acid (18.59 and 14.21 µg ml- 1), trehalose (28.35 and 22.74 µg mg- 1 FW) and glycine betaine (11.35 and 7.74 mg g- 1) respectively. AC06 and BA01 strains were further evaluated for their multifunctional performance by inoculating in Arachis hypogaea L. (Groundnut) under mild and severe drought regimes (60 and 40% Field Capacity). Inoculation with microbial biostimulants displayed distinct osmotic-adjustment abilities of the groundnut, such as growth parameters, plant biomass, photosynthetic pigments, relative water content, proline, and soluble sugar in respective to control during drought. On the other hand, plant sensitivity indexes such as electrolyte leakage and malondialdehyde (MDA) contents were decreased as well as cooperatively conferred plant drought tolerance by induced alterations in stress indicators such as catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD). Thus, Acinetobacter sp. AC06 and Bacillus sp. BA01 can be considered as osmolyte producing microbial biostimulants to simultaneously induce osmotic tolerance and metabolic changes in groundnuts under drought stress.

Unveiling stress-adapted endophytic bacteria: Characterizing plant growth-promoting traits and assessing cross-inoculation effects on Populus deltoides under abiotic stress.

In the face of the formidable environmental challenges precipitated by the ongoing climate change, Plant Growth-Promoting Bacteria (PGPB) are gaining widespread acknowledgement for their potential as biofertilizers, biocontrol agents, and microbial inoculants. However, a knowledge gap pertains to the ability of PGPB to improve stress tolerance in forestry species via cross-inoculation. To address this gap, the current investigation centres on PGPBs, namely, Acinetobacter johnsonii, Cronobacter muytjensii, and Priestia endophytica, selected from the phyllosphere of robust and healthy plants thriving in the face of stress-inducing conditions. These strains were selected based on their demonstrated adaptability to saline, arid, and nitrogen-deficient environments. The utilization of PGPB treatment resulted in an improvement of stomatal conductance (gs) and transpiration rate (E) in poplar plants exposed to both salt and drought stress. It also induced an increase in essential biochemical components such as proline (PRO), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). These reactions were accompanied by a decrease in leaf malonaldehyde (MDA) content and electrolyte leakage (EL). Furthermore, the PGPB treatment demonstrated a notable enhancement in nutrient absorption, particularly nitrogen and carbon, achieved through the solubilization of nutrients. The estimation of canopy temperature via thermal imaging proved to be an efficient method for distinguishing stress reactions in poplar than conventional temperature recording techniques. In summation, the utilization of PGPB especially Cronobacter muytjensii in this study, yielded profound improvements in the stress tolerance of poplar plants, manifesting in reduced membrane lipid peroxidation, enhanced photosynthesis, and bolstered antioxidant capacity within the leaves.

Coculture of Acinetobacter johnsonii and Shewanella putrefaciens Contributes to the ABC Transporter that Impacts Cold Adaption in the Aquatic Food Storage Environment.

Acinetobacter johnsonii and Shewanella putrefaciens were identified as specific spoilage organisms in aquatic food. The interactions among specific spoilage organisms under cold stress have a significant impact on the assembly of microbial communities, which play crucial roles in the spoilage and cold adaptation processes. The limited understanding of A. johnsonii and S. putrefaciens interactions in the cold adaptation mechanism hinders the elucidation of their roles in protein and metabolism levels. 4D quantitative proteomic analysis showed that the coculture of A. johnsonii and S. putrefaciens responds to low temperatures through ABC transporter proteins, resulting in phospholipid transport and inner membrane components. SapA and FtsX proteins were significantly upregulated, while LolC, LolD, LolE, PotD, PotA, PotB, and PotC proteins were significantly downregulated. Metabolome assays revealed that metabolites of glutathione and spermidine/putrescin were significantly upregulated, while metabolites of arginine/lysine/ornithine were significantly downregulated and involved in the ABC transporter metabolism. The results of ultramicroscopic analyses showed that the coculture of A. johnsonii and S. putrefaciens surface combined with the presence of the leakage of intracellular contents, suggesting that the bacteria were severely damaged and wrinkled to absorb metabolic nutrients and adapt to cold temperatures.

Acinetobacter quorum sensing contributes to inflammation-induced inhibition of orthopaedic implant osseointegration.

Implant infection impairs osseointegration of orthopaedic implants by inducing inflammation. Acinetobacter spp. are increasingly prevalent multi-drug resistant bacteria that can cause osteomyelitis. Acinetobacter spp. can also cause inflammation and thereby inhibit osseointegration in mice. The purpose of the present study was to investigate the role of quorum sensing in this context. Therefore, wild-type bacteria were compared with an isogenic abaI mutant defective in quorum sensing in a murine osseointegration model. The abaI quorum- sensing mutant affected significantly less osseointegration and interleukin (IL) 1ß levels, without detectably altering other pro-inflammatory cytokines. Wild-type bacteria had fewer effects on IL1 receptor (IL1R)-/- mice. These results indicated that quorum sensing in Acinetobacter spp. contributed to IL1ß induction and the resultant inhibition of osseointegration in mice. Moreover, targeting the Gram-negative acyl-homoserine lactone quorum sensing may be particularly effective for patients with Acinetobacter spp. infections.

Identification and characterization of the WYL BrxR protein and its gene as separable regulatory elements of a BREX phage restriction system.

Bacteriophage exclusion ('BREX') phage restriction systems are found in a wide range of bacteria. Various BREX systems encode unique combinations of proteins that usually include a site-specific methyltransferase; none appear to contain a nuclease. Here we describe the identification and characterization of a Type I BREX system from Acinetobacter and the effect of deleting each BREX ORF on growth, methylation, and restriction. We identified a previously uncharacterized gene in the BREX operon that is dispensable for methylation but involved in restriction. Biochemical and crystallographic analyses of this factor, which we term BrxR ('BREX Regulator'), demonstrate that it forms a homodimer and specifically binds a DNA target site upstream of its transcription start site. Deletion of the BrxR gene causes cell toxicity, reduces restriction, and significantly increases the expression of BrxC. In contrast, the introduction of a premature stop codon into the BrxR gene, or a point mutation blocking its DNA binding ability, has little effect on restriction, implying that the BrxR coding sequence and BrxR protein play independent functional roles. We speculate that elements within the BrxR coding sequence are involved in cis regulation of anti-phage activity, while the BrxR protein itself plays an additional regulatory role, perhaps during horizontal transfer.

Clinical Isolates of Acinetobacter spp. Are Highly Serum Resistant Despite Efficient Recognition by the Complement System.

Gram-negative bacteria from the genus Acinetobacter are responsible for life-threating hospital-related infections such as pneumonia, septicemia, and meningitis, especially in immunocompromised patients. Worryingly, Acinetobacter have become multi- and extensively drug resistant (MDR/XDR) over the last few decades. The complement system is the first line of defense against microbes, thus it is highly important to increase our understanding of evasion mechanisms used by Acinetobacter spp. Here, we studied clinical isolates of Acinetobacter spp. (n=50), aiming to characterize their recognition by the complement system. Most isolates tested survived 1 h incubation in 30% serum, and only 8 isolates had a lower survival rate, yet none of those isolates were fully killed. Intriguingly, four isolates survived in human whole blood containing all cell component. Their survival was, however, significantly reduced. Flow cytometry analyses revealed that most of the isolates were detected by human IgG and IgM. Interestingly, we could not detect any significant concentration of deposited C1q, despite observing C4b deposition that was abolished in C1q-deficient serum, indicating transient binding of C1q to bacteria. Moreover, several isolates were recognized by MBL, with C4b deposition abolished in MBL-deficient serum. C3b was deposited on most isolates, but this was not, however, seen with respect to C5b and formation of the membrane attack complex (MAC), indicating that many isolates could avoid complement-mediated lysis. India ink staining showed that isolates were capsulated, and capsule thickness varied significantly between isolates. Studies performed on a wild-type strain and capsule mutant strains, demonstrated that the production of a capsular polysaccharide is one mechanism that mediates resistance to complement-mediated bactericidal activity by preventing MAC deposition and lysis. Our data showed that most clinical Acinetobacter spp. isolates are highly serum resistant despite being efficiently recognized by the complement system.

Altered gut microbiota correlated with systemic inflammation in children with Kawasaki disease.

Kawasaki disease (KD) is a multi-systemic vasculitis of unknown etiology that occurs mainly in children, and the disturbance of gut microbiota is generally believed to cause a hyperimmune reaction triggering KD. The aim of the study was to investigate the alterations in the fecal microbiota and assess its relationship with systemic inflammation. Totally 30 KD children were enrolled and followed up for 6 months, with another group of 30 age- and sex-matched healthy children as controls. Phylotype profiles of fecal microbial communities were analyzed using 16S rRNA gene sequencing. Serum inflammatory markers were detected by flow cytometer. We showed that KD children exhibited a significant reduction in fecal microbial diversity in the acute phase compared with the healthy controls. Enterococcus, Acinetobacter, Helicobacter, Lactococcus, Staphylococcus and Butyricimonas in acute KD children were significantly higher than the healthy children. Levels of systemic inflammation biomarkers, including IL-2, IL-4, IL-6, IL-10, TNF-α, and INF-γ, were significantly elevated in the acute KD children. Altered microbiota genera Enterococcus and Helicobacter abundances were shown to be correlated positively with IL-6, which were never previously reported in KD. This study suggested that gut microbiota alteration is closely associated with systemic inflammation, which provides a new perspective on the etiology and pathogenesis of KD.

Characterization of Acinetobacter chengduensis sp. nov., isolated from hospital sewage and capable of acquisition of carbapenem resistance genes.

Two strains of the genus Acinetobacter, WCHAc060005T and WCHAc060007, were isolated from hospital sewage in China. The two strains showed different patterns of resistance to clinically important antibiotics and their taxonomic positions were investigated. Cells are Gram-negative, obligate aerobic, non-motile, catalase-positive and oxidase-negative coccobacilli. A preliminary analysis based on the 16S rRNA gene sequences indicated that the two strains had the highest similarity to Acinetobacter cumulans WCHAc060092T (99.02%). Whole-genome sequencing of the two strains and genus-wide phylogeny reconstruction based on a set of 107 Acinetobacter core genes indicated that they formed a separate and internally cohesive clade within the genus. The average nucleotide identity based on BLAST and in silico DNA-DNA hybridization values between the two new genomes were 99.77% and 98.7% respectively, whereas those between the two genomes and the known Acinetobacter species were <88.93% and <34.0%, respectively. A total of 7 different genes were found in the two genome sequences which encode resistance to five classes of antimicrobial agents, including clinically important carbapenems, oxyimino-cephalosporins, and quinolones. In addition, the combination of their ability to assimilate gentisate, but not l-glutamate and d,l-lactate could distinguish the two strains from all known Acinetobacter species. Based on these combined data, we concluded that the two strains represent a novel species of the genus Acinetobacter, for which the name Acinetobacter chengduensis sp. nov. is proposed. The type strain is WCHAc060005T (CCTCC AB 2019139=GDMCC 1.1622=JCM 33509).

Protective Role of Bacterial Alkanesulfonate Monooxygenase under Oxidative Stress.

Bacterial alkane metabolism is associated with a number of cellular stresses, including membrane stress and oxidative stress, and the limited uptake of charged ions such as sulfate. In the present study, the genes ssuD and tauD in Acinetobacter oleivorans DR1 cells, which encode an alkanesulfonate monooxygenase and a taurine dioxygenase, respectively, were found to be responsible for hexadecanesulfonate (C16SO3H) and taurine metabolism, and Cbl was experimentally identified as a potential regulator of ssuD and tauD expression. The expression of ssuD and tauD occurred under sulfate-limited conditions generated during n-hexadecane degradation. Interestingly, expression analysis and knockout experiments suggested that both genes are required to protect cells against oxidative stress, including that generated by n-hexadecane degradation and H2O2 exposure. Measurable levels of intracellular hexadecanesulfonate were also produced during n-hexadecane degradation. Phylogenetic analysis suggested that ssuD and tauD are mainly present in soil-dwelling aerobes within the Betaproteobacteria and Gammaproteobacteria classes, which suggests that they function as controllers of the sulfur cycle and play a protective role against oxidative stress in sulfur-limited conditions.IMPORTANCEssuD and tauD, which play a role in the degradation of organosulfonate, were expressed during n-hexadecane metabolism and oxidative stress conditions in A. oleivorans DR1. Our study confirmed that hexadecanesulfonate was accidentally generated during bacterial n-hexadecane degradation in sulfate-limited conditions. Removal of this by-product by SsuD and TauD must be necessary for bacterial survival under oxidative stress generated during n-hexadecane degradation.

Regulation of the AcrAB efflux system by the quorum-sensing regulator AnoR in Acinetobacter nosocomialis.

Multidrug efflux pumps play an important role in antimicrobial resistance and pathogenicity in bacteria. Here, we report the functional characterization of the RND (resistance-nodulation- division) efflux pump, AcrAB, in Acinetobacter nosocomialis. An in silico analysis revealed that homologues of the AcrAB efflux pump, comprising AcrA and AcrB, are widely distributed among different bacterial species. Deletion of acrA and/or acrB genes led to decreased biofilm/pellicle formation and reduced antimicrobial resistance in A. nosocomialis. RNA sequencing and mRNA expression analyses showed that expression of acrA/B was downregulated in a quorum sensing (QS) regulator (anoR)-deletion mutant, indicating transcriptional activation of the acrAB operon by AnoR in A. nosocomialis. Bioassays showed that secretion of N-acyl homoserine lactones (AHLs) was unaffected in acrA and acrB deletion mutants; however, AHL secretion was limited in a deletion mutant of acrR, encoding the acrAB regulator, AcrR. An in silico analysis indicated the presence of AcrR-binding motifs in promoter regions of anoI (encoding AHL synthase) and anoR. Specific binding of AcrR was confirmed by electrophoretic mobility shift assays, which revealed that AcrR binds to positions -214 and -217 bp upstream of the translational start sites of anoI and anoR, respectively, demonstrating transcriptional regulation of these QS genes by AcrR. The current study further addresses the possibility that AcrAB is controlled by the osmotic stress regulator, OmpR, in A. nosocomialis. Our data demonstrate that the AcrAB efflux pump plays a crucial role in biofilm/pellicle formation and antimicrobial resistance in A. nosocomialis, and is under the transcriptional control of a number of regulators. In addition, the study emphasizes the interrelationship of QS and AcrAB efflux systems in A. nosocomialis.

Histidine Utilization Is a Critical Determinant of Acinetobacter Pathogenesis.

Acinetobacter baumannii is a nosocomial pathogen capable of causing a range of diseases, including respiratory and urinary tract infections and bacteremia. Treatment options are limited due to the increasing rates of antibiotic resistance, underscoring the importance of identifying new targets for antimicrobial development. During infection, A. baumannii must acquire nutrients for replication and survival. These nutrients include carbon- and nitrogen-rich molecules that are needed for bacterial growth. One possible nutrient source within the host is amino acids, which can be utilized for protein synthesis or energy generation. Of these, the amino acid histidine is among the most energetically expensive for bacteria to synthesize; therefore, scavenging histidine from the environment is likely advantageous. We previously identified the A. baumannii histidine utilization (Hut) system as being linked to nutrient zinc homeostasis, but whether the Hut system is important for histidine-dependent energy generation or vertebrate colonization is unknown. Here, we demonstrate that the Hut system is conserved among pathogenic Acinetobacter and regulated by the transcriptional repressor HutC. In addition, the Hut system is required for energy generation using histidine as a carbon and nitrogen source. Histidine was also detected extracellularly in the murine lung, demonstrating that it is bioavailable during infection. Finally, the ammonia-releasing enzyme HutH is required for acquiring nitrogen from histidine in vitro, and strains inactivated for hutH are severely attenuated in a murine model of pneumonia. These results suggest that bioavailable histidine in the lung promotes Acinetobacter pathogenesis and that histidine serves as a crucial nitrogen source during infection.

Acinetobacter pullorum sp. nov., Isolated from Chicken Meat.

A bacterial strain, designated B301T and isolated from raw chicken meat obtained from a local market in Korea, was characterized and identified using a polyphasic taxonomic approach. Cells were gram-negative, non-motile, obligate-aerobic coccobacilli that were catalase-positive and oxidase-negative. The optimum growth conditions were 30°C, pH 7.0, and 0% NaCl in tryptic soy broth. Colonies were round, convex, smooth, and cream-colored on tryptic soy agar. Strain B301T has a genome size of 3,102,684 bp, with 2,840 protein-coding genes and 102 RNA genes. The 16S rRNA gene analysis revealed that strain B301T belongs to the genus Acinetobacter and shares highest sequence similarity (97.12%) with A. celticus ANC 4603T and A. sichuanensis WCHAc060041T. The average nucleotide identity and digital DNA-DNA hybridization values for closely related species were below the cutoff values for species delineation (95-96% and 70%, respectively). The DNA G+C content of strain B301T was 37.0%. The major respiratory quinone was Q-9, and the cellular fatty acids were primarily summed feature 3 (C16:1 ω6c/C16:1 ω7c), C16:0, and C18:1 ω9c. The major polar lipids were phosphatidylethanolamine, diphosphatidyl-glycerol, phosphatidylglycerol, and phosphatidyl-serine. The antimicrobial resistance profile of strain B301T revealed the absence of antibiotic-resistance genes. Susceptibility to a wide range of antimicrobials, including imipenem, minocycline, ampicillin, and tetracycline, was also observed. The results of the phenotypic, chemotaxonomic, and phylogenetic analyses indicate that strain B301T represents a novel species of the genus Acinetobacter, for which the name Acinetobacter pullorum sp. nov. is proposed. The type strain is B301T (=KACC 21653T = JCM 33942T).

Flower-like patterns in multi-species bacterial colonies.

Diverse interactions among species within bacterial colonies lead to intricate spatiotemporal dynamics, which can affect their growth and survival. Here, we describe the emergence of complex structures in a colony grown from mixtures of motile and non-motile bacterial species on a soft agar surface. Time-lapse imaging shows that non-motile bacteria 'hitchhike' on the motile bacteria as the latter migrate outward. The non-motile bacteria accumulate at the boundary of the colony and trigger an instability that leaves behind striking flower-like patterns. The mechanism of the front instability governing this pattern formation is elucidated by a mathematical model for the frictional motion of the colony interface, with friction depending on the local concentration of the non-motile species. A more elaborate two-dimensional phase-field model that explicitly accounts for the interplay between growth, mechanical stress from the motile species, and friction provided by the non-motile species, fully reproduces the observed flower-like patterns.

Communities of bacteria and other microbes live in every ecosystem on Earth, including in soil, in hydrothermal vents, on the surface of plants and in the human gut. They often attach to solid surfaces and form dense colonies called biofilms. Most biofilms found in nature are comprised of many different species of bacteria. How the bacteria interact shapes the internal structures of these communities. Many previous studies have focused on the molecules that bacteria use to relate to each other, for example, some bacteria exchange nutrients or release toxins that are harmful to their neighbors. However, it is less clear how direct physical contacts between bacteria affect the whole community. Escherichia coli is a rod-shaped bacterium that is a good swimmer, but has a hard time moving on solid surfaces. Therefore, when a droplet of liquid containing these bacteria is placed in a Petri dish containing a jelly-like substance called agar, the droplet barely expands over a 24-hour period. On the other hand, a droplet containing another rod-shaped bacterium known as Acinetobacter baylyi expands rapidly on agar because these bacteria are able to crawl using microscopic "legs" called pili. Here, Xiong et al. set out to investigate how a colony containing both E. coli and A. baylyi developed on a solid surface. The experiments showed that when a droplet of liquid containing both species was placed on agar, both species grew and spread rapidly, as if the E. coli hitchhiked on the highly motile A. baylyi cells. Furthermore, the growing colony developed a complex flower-like shape. Xiong et al. developed mathematical models that took into account how quickly each species generally grows, their ability to move, the friction between cells and the agar, and other physical properties. The models predicted that the E. coli cells that accumulate at the expanding boundary of the colony make the boundary unstable, leading to the flower-like patterns. Further analysis suggested that similar patterns may form in other situations when motile and non-motile species of bacteria are together. These findings may help us understand the origins of the complex structures observed in many naturally occurring communities of bacteria.

OxyR-controlled surface polysaccharide production and biofilm formation in Acinetobacter oleivorans DR1.

The genomes of several Acinetobacter species possess three distinct polysaccharide-producing operons [two poly-N-acetyl glucosamine (PNAG) and one K-locus]. Using a microfluidic device, an increased amount of polysaccharides and enhanced biofilm formation were observed following continuous exposure to H2O2 and removal of the H2O2-sensing key regulator, OxyR, in Acinetobacter oleivorans DR1 cells. Gene expression analysis revealed that genes located in PNAG1, but not those in PNAG2, were induced and that genes in the K-locus were expressed in the presence of H2O2. Interestingly, the expression of the K-locus gene was enhanced in the PNAG1 mutant and vice versa. The absence of either OxyR or PNAG1 resulted in enhanced biofilm formation, higher surface hydrophobicity, and increased motility, implying that K-locus-driven polysaccharide production in both the oxyR and PNAG1 deletion mutants may be related to these phenotypes. Both the oxyR and K-locus deletion mutants were more sensitive to H2O2 compared with the wildtype and PNAG1 mutant strains. Purified OxyR binds to the promoter regions of both polysaccharide operons with a higher affinity toward the K-locus promoter. Although oxidized OxyR could bind to both promoter regions, the addition of dithiothreitol further enhanced the binding efficiency of OxyR, suggesting that OxyR might function as a repressor for controlling these polysaccharide operons.

High fat diet induces microbiota-dependent silencing of enteroendocrine cells.

Enteroendocrine cells (EECs) are specialized sensory cells in the intestinal epithelium that sense and transduce nutrient information. Consumption of dietary fat contributes to metabolic disorders, but EEC adaptations to high fat feeding were unknown. Here, we established a new experimental system to directly investigate EEC activity in vivo using a zebrafish reporter of EEC calcium signaling. Our results reveal that high fat feeding alters EEC morphology and converts them into a nutrient insensitive state that is coupled to endoplasmic reticulum (ER) stress. We called this novel adaptation 'EEC silencing'. Gnotobiotic studies revealed that germ-free zebrafish are resistant to high fat diet induced EEC silencing. High fat feeding altered gut microbiota composition including enrichment of Acinetobacter bacteria, and we identified an Acinetobacter strain sufficient to induce EEC silencing. These results establish a new mechanism by which dietary fat and gut microbiota modulate EEC nutrient sensing and signaling.

PilT and PilU are homohexameric ATPases that coordinate to retract type IVa pili.

Bacterial type IV pili are critical for diverse biological processes including horizontal gene transfer, surface sensing, biofilm formation, adherence, motility, and virulence. These dynamic appendages extend and retract from the cell surface. In many type IVa pilus systems, extension occurs through the action of an extension ATPase, often called PilB, while optimal retraction requires the action of a retraction ATPase, PilT. Many type IVa systems also encode a homolog of PilT called PilU. However, the function of this protein has remained unclear because pilU mutants exhibit inconsistent phenotypes among type IV pilus systems and because it is relatively understudied compared to PilT. Here, we study the type IVa competence pilus of Vibrio cholerae as a model system to define the role of PilU. We show that the ATPase activity of PilU is critical for pilus retraction in PilT Walker A and/or Walker B mutants. PilU does not, however, contribute to pilus retraction in ΔpilT strains. Thus, these data suggest that PilU is a bona fide retraction ATPase that supports pilus retraction in a PilT-dependent manner. We also found that a ΔpilU mutant exhibited a reduction in the force of retraction suggesting that PilU is important for generating maximal retraction forces. Additional in vitro and in vivo data show that PilT and PilU act as independent homo-hexamers that may form a complex to facilitate pilus retraction. Finally, we demonstrate that the role of PilU as a PilT-dependent retraction ATPase is conserved in Acinetobacter baylyi, suggesting that the role of PilU described here may be broadly applicable to other type IVa pilus systems.

Sequential electrochemical oxidation and bio-treatment of the azo dye congo red and textile effluent.

Textile effluent is often difficult to manage as it contains a high concentration of toxic and recalcitrant synthetic dyes. In this study, congo Red and textile effluent were treated by electrochemical oxidation using RuO2-IrO2 coated titanium electrode as an anode followed by biodecolorization using Pseudomonas stutzeri MN1 and Acinetobacter baumannii MN3. Effluent pre-treatment is often necessary to minimize the inhibitory effects of textile dyes on dye degrading bacterial during bio-treatment. The pre-treatment of Congo Red by electrochemical oxidation for 10 min resulted in a decolorization rate of 98% at a pH, NaCl concentration, and current density of 7, 2 g L-1, and 20 mA cm-2. Subsequent bio-treatment of the pretreated Congo Red enhanced the biodegradation to 93%. The COD removal efficiency in real textile effluent following electrochemical pretreatment and biological treatment using bacterial consortium were 3.8% and 93%, respectively. Therefore, integrating electrochemical oxidation and microbial consortia offers an effective and environmentally friendly approach for treating complex industrial effluents.

Use of silicon nanoparticle surface coating in infection control: Experience in a tropical healthcare setting.

BACKGROUND: A nano-scale surface coating containing silicon nanoparticles (Bacterlon®) creates a hydrophobic surface which prevents the growth of bacteria. Study objective was to evaluate the performance of this silicon nano-coating in Sri Lankan healthcare setting. METHODS: This prospective study was conducted from September 2015 to December 2015 in an Intensive Care Unit and a medical ward in Base Hospital Homagama and a bacteriology laboratory in Medical Research Institute, Colombo, Sri Lanka. Silicon nanoparticle coating was applied to 19 high touch surfaces from those three sites. During the follow-up period, these test sites and non-coated control sites were used for routine work and were cleaned routinely as per institute protocol. Swabbing was done for coated and non-coated sites once a week for 12 weeks at unannounced times. Surfaces were categorized in to low (≤10 CFU/cm2) and high (>10-99 CFU/cm2) contamination by Aerobic Bacterial Count (ABC) in non-coated sites at any given time. RESULTS: In low and high contaminated surfaces, an improvement in the mean percentage bioburden reduction from 36.18% to 50.16% was observed from 4th week to 12th week with silicon nanoparticles and a significant reduction (p < 0.05) was seen in ABC in each of the coated surface compared with their non-coated counterpart by the 12th week. The frequency of isolation of Acinetobacter spp. on coated surfaces had a significant reduction (p < 0.01). CONCLUSION: Silicon nanoparticle coating demonstrates a significant reduction of the bacterial bioburden in low and high contaminated surfaces for 12 weeks in a tropical healthcare setting.

Specimen Collection, Processing, Culture, and Biochemical Identification of Acinetobacter spp.

Specimen collection and processing is an important aspect of clinical microbiology laboratory. The reports are dependent on the quality of the specimen and the time between the collection and processing. Appropriate methodology needs to be followed for the collection, amount, type, labeling, transportation, and processing of the specimens especially for organism like Acinetobacter species. Various biochemical tests are used for identification of various organisms. Such identification depends on the ability of organisms to produce certain enzymes or to utilize certain compound to be identified by biochemical tests.