Effect of yeast extract on microbiologically influenced corrosion of X70 pipeline steel by Desulfovibrio bizertensis SY-1.

Microbiologically influenced corrosion (MIC) is a complicated process that happens ubiquitously and quietly in many fields. As a useful nutritional ingredient in microbial culture media, yeast extract (YE) is a routinely added in the MIC field. However, how the YE participated in MIC is not fully clarified. In the present work, the effect of YE on the growth of sulfate reducing prokaryotes (SRP) Desulfovibrio bizertensis SY-1 and corrosion behavior of X70 pipeline steel were studied. It was found that the weight loss of steel coupons in sterile media was doubled when YE was removed from culture media. However, in the SRP assays without YE the number of planktonic cells decreased, but the attachment of bacteria on steel surfaces was enhanced significantly. Besides, the corrosion rate of steel in SRP assays increased fourfold after removing YE from culture media. MIC was not determined for assays with planktonic SRP but only for biofilm assays. The results confirm the effect of YE on D. bizertensis SY-1 growth and also the inhibitory role of YE on MIC.

Human access and deterministic processes play a major role in structuring planktonic and sedimentary bacterial and eukaryotic communities in lakes.

Lakes provide habitat for a diverse array of species and offer a wide range of ecosystem services for humanity. However, they are highly vulnerable as they are not only impacted by adverse actions directly affecting them, but also those on the surrounding environment. Improving knowledge on the processes responsible for community assembly in different biotic components will aid in the protection and restoration of lakes. Studies to date suggested a combination of deterministic (where biotic/abiotic factors act on fitness differences amongst taxa) and stochastic (where dispersal plays a larger factor in community assembly) processes are responsible for structuring biotic communities, but there is no consensus on the relative roles these processes play, and data is lacking for lakes. In the present study, we sampled different biotic components in 34 lakes located on the South Island of New Zealand. To obtain a holistic view of assembly processes in lakes we used metabarcoding to investigate bacteria in the sediment and surface waters, and eukaryotes in the sediment and two different size fractions of the water column. Physicochemical parameters were collected in parallel. Results showed that deterministic processes dominated the assembly of lake communities although the relative importance of variable and homogeneous selection differed among the biotic components. Variable selection was more important in the sediment (SSbact and SSeuks) and for the bacterioplankton (Pbact) while the assembly of the eukaryotic plankton (SPeuks, LPeuks) was driven more by homogeneous selection. The ease of human access to the lakes had a significant effect on lake communities. In particular, clade III of SAR11 and Daphnia pulex were only present in lakes with public access. This study provides insights into the distribution patterns of different biotic components and highlights the value in understanding the drivers of different biological communities within lakes.

Composition and functionality of bacterioplankton communities in marine coastal zones adjacent to finfish aquaculture.

Finfish aquaculture is a fast-growing primary industry and is increasingly common in coastal ecosystems. Bacterioplankton is ubiquitous in marine environment and respond rapidly to environmental changes. Changes in bacterioplankton community are not well understood in semi-enclosed stratified embayments. This study aims to examine aquaculture effects in the composition and functional profiles of the bacterioplankton community using amplicon sequencing along a distance gradient from two finfish leases in a marine embayment. Results revealed natural stratification in bacterioplankton associated to NOx, conductivity, salinity, temperature and PO4. Among the differentially abundant bacteria in leases, we found members associated with nutrient enrichment and aquaculture activities. Abundant predicted functions near leases were assigned to organic matter degradation, fermentation, and antibiotic resistance. This study provides a first effort to describe changes in the bacterioplankton community composition and function due to finfish aquaculture in a semi-enclosed and highly stratified embayment with a significant freshwater input.

Comparison of bacterial communities on the surface of concrete breakwater structures and ambient bacterioplankton.

Breakwater structures made of concrete are used widely around the world, and the bacteria living on these surfaces can cause the concrete to deteriorate. In this study, we collected bacterial biofilms from concrete breakwater structures located along the coast of an island, a mainland coast, and a freshwater riverbank as well as planktonic water samples from each site, and we analysed their bacterial community structures using Illumina sequencing. At the phylum level, Proteobacteria and Actinobacteria dominated planktonic samples, whereas Cyanobacteria, Proteobacteria and Bacteroidetes dominated the biofilm samples. High Cyanobacteria abundance was found in all biofilm samples. Bacterial communities significantly varied between planktonic and biofilm samples and between biofilm samples from seawater and freshwater. Only a small number of bacterial operational taxonomic units were shared by planktonic and biofilm samples from each sampling site. The permanganate index in ambient water had a more significant impact on biofilm bacterial communities than on planktonic samples. Additionally, ammonia nitrogen and total nitrogen contents were positively correlated and salinity was negatively correlated with bacterial beta diversity in biofilm samples.

Damming river shapes distinct patterns and processes of planktonic bacterial and microeukaryotic communities.

Planktonic bacterial and microeukaryotic communities play important roles in biogeochemical cycles, but their biogeographic patterns and community assembly processes in large damming rivers still remain unclear. In this study, 16S rRNA and 18S rRNA coding genes were used for sample sequencing analysis of planktonic bacterial and microeukaryotic communities in the upper Yangtze River. The upper Yangtze River was divided into dam-affected zones and river zones based on the influence of dams. The results showed that there were significant differences in the bacterial and microeukaryotic communities between the two zones and that dams significantly reduced the α-diversity of the bacterial communities. Co-occurrence network analysis indicated that networks in the river zone were denser than those in the dam-affected zone. The relationships among species in bacterial networks were more complex than those in microeukaryotic networks. Dispersal limitation and ecological drift were the main processes influencing planktonic bacterial and microeukaryotic communities in the dam-affected zone respectively, whereas the role of deterministic processes increased in the river zone. Anthropogenic activities and hydraulic conditions affected suspended sediment and controlled microbial diversity in the river zone. These results suggest that dams impact planktonic bacteria more strongly than planktonic microeukaryotes, indicating that the distribution patterns and processes of the bacterial and microeukaryotic communities in large rivers are significantly different.

Patchy Distributions and Distinct Niche Partitioning of Mycoplankton Populations across a Nearshore to Open Ocean Gradient.

Evidence increasingly suggests planktonic fungi (or mycoplankton) play an important role in marine food webs and biogeochemical cycles. In order to better understand their ecological role and how oceanographic gradients from the coastal to open ocean shape the mycoplankton community, molecular approaches were used to study fungal dynamics along a repeatedly sampled, five-station transect beginning at the mouth of an estuary and continuing 87 km across the continental shelf to the oligotrophic waters at the boundary of the Sargasso Sea. Similar to patterns in chlorophyll a, fungal 18S rRNA gene abundance showed a sharp decrease from nearshore to offshore stations. While Shannon's diversity was not statistically different across the transect, nonmetric multidimensional scaling (NMDS) ordination revealed that fungal communities at the nearshore station were significantly different from those at other stations. Even though spatial gradients were consistently strong, the shelf mycoplankton were more similar to those of the offshore communities when temperature was high (>20°C) and while they shifted toward the nearshore communities when temperature was low (<19°C), suggesting a role for additional seasonal factors (such as temperature) in shaping mycoplankton distributions. However, overall phylotype distributions were patchy with few taxa observed at all stations and the majority observed at a single station with the nearshore station exhibiting the largest number of exclusive phylotypes. Overall, our findings revealed the patchy spatial distributions and distinct niche partitioning of mycoplankton populations across a nearshore to open ocean gradient, which improved our understanding of fungal ecology in coastal waters. IMPORTANCE Fungi are an important, but understudied, group of heterotrophic microbes in marine environments. Traditionally, fungi in the coastal ocean were largely assumed to be derived from terrestrial inputs. Yet here we find many fungal taxa are endemic to the open ocean environment but are rare or absent in nearshore waters, suggesting they are not washed into the ocean from the land. As observed for the bacterioplankton, coastal oceanographic gradients can function as habitat barriers to partition fungal communities. Compared to the bacterioplankton, however, the mycoplankton exhibit a much patchier distribution pattern, suggesting differential drivers and the potential for spatially/temporally limited habitats or strong density-dependent selection. Therefore, our results show that mycoplankton in the coastal ocean may play a significant but complementary role to that of the bacterioplankton.

Pipeline for Analyzing Activity of Metabolic Pathways in Planktonic Communities Using Metatranscriptomic Data.

In this article, we present our novel pipeline for analysis of metabolic activity using a microbial community's metatranscriptome sequence data set for validation. Our method is based on expectation-maximization (EM) algorithm and provides enzyme expression and pathway activity levels. Further expanding our analysis, we consider individual enzymatic activity and compute enzyme participation coefficients to approximate the metabolic pathway activity more accurately. We apply our EM pathways pipeline to a metatranscriptomic data set of a plankton community from surface waters of the Northern Gulf of Mexico. The data set consists of RNA-seq data and respective environmental parameters, which were sampled at two depths, six times a day over multiple 24-hour cycles. Furthermore, we discuss microbial dependence on day-night cycle within our findings based on a three-way correlation of the enzyme expression during antipodal times-midnight and noon. We show that the enzyme participation levels strongly affect the metabolic activity estimates: that is, marginal and multiple linear regression of enzymatic and metabolic pathway activity correlated significantly with the recorded environmental parameters. Our analysis statistically validates that EM-based methods produce meaningful results, as our method confirms statistically significant dependence of metabolic pathway activity on the environmental parameters, such as salinity, temperature, brightness, and a few others.

Evaluation of the differences between biofilm and planktonic Brucella abortus via metabolomics and proteomics.

This study analyzed the difference between biofilm and planktonic Brucella abortus using metabolomics and proteomics. Brucella abortus was cultured in different media to induce Brucella abortus biofilm formation and planktonic cells, followed by metabolomics and proteomics analyses for these two samples. Significant differential metabolites were identified, followed by KEGG pathway analysis. Differentially expressed proteins were identified, followed by subcellular localization, GO annotation, and KEGG pathway enrichment. Additionally, a correlation analysis of metabolomics and proteomics was performed. Metabolomics analysis showed 7682 positive and 4433 negative metabolites, including 188 positive and 117 negative significant differential metabolites. These differential metabolites were enriched in fatty acid/unsaturated fatty acid biosynthesis and linoleic acid metabolism. Proteomics analysis revealed 1759 proteins, including 486 differentially expressed proteins, which were enriched in various metabolic and degradation-related pathways. Subcellular localization showed that 74.3% of the differential proteins were cytoplasmic proteins. Correlation analysis showed that 1-palmitoyl-2-oleoyl-phosphatidylglycerol had the most significant correlations with proteins, followed by cytosine. Both metabolites correlated with the protein Q57EI7 (RbsB-1, ribose ABC transporter). One common pathway, fatty acid biosynthesis, was identified by both proteomics and metabolomics analyses that involved the metabolites, oleic acid, and protein Q57DK3 (biotin carboxylase). There were metabolomic and proteomic differences between Brucella abortus biofilm and planktonic cells, and these results provide novel insights into the biofilm-forming process of Brucella abortus.

Physiological studies of the Pediococcus pentosaceus biofilm.

Pediococcus pentosaceus, a bacterium recently used in human and animal probiotics, was used in combination with supports made from polylactic acid composite soybean meal was used to study biofilm formation, and it was found that dense biofilms developed by Day 1. Proteomic comparison between planktonic and biofilm cultures of P. pentosaceus showed distinct expression patterns of intracellular and extracellular proteins. Type I glyceraldehyde-3-phosphate dehydrogenase was upregulated in biofilm cultures and mediated cell adhesion and encouraged biofilm production. GMP synthase, which regulates GMP synthesis and acts as an intracellular signal molecule to control cell mechanisms and has been exploited in the development of new therapeutic agents, was also upregulated in the biofilm mode of growth. The present work serves as a basis for future studies examining the complex network of systems that regulate lactic acid bacterial (LAB) biofilm formation and can serve as a framework for studies of production of therapeutic agents from LAB.

Planktonic and sediment bacterial communities in an integrated mariculture system.

An integrated multi-trophic aquaculture (IMTA) system, with one fish cage model surrounded by an island and shellfish rafts, was used in the current study. Planktonic and sediment bacterial communities in the IMTA system were monitored over four seasons in 2019. In both plankton and sediment samples, the most dominant phyla were Proteobacteria and Bacteroidota. Sediment bacterial samples were more similar and had higher levels of biodiversity than planktonic bacterial samples. Obvious seasonal variations were found in plankton samples, but not in sediment samples. No obvious inter-site variations in planktonic and sediment bacteria (fish cages, shellfish rafts and control sites) were found and the results suggested that no obvious impact of feeding operations in fish culture cage model on bacterial communities in the IMTA system was observed in this study. Based on the sequence data, some faecal indicator bacteria and potentially pathogenic bacterial species were detected. According to the results, the bacterial water quality in the IMTA system was acceptable. PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) analysis revealed that the primary difference in potential functional roles of planktonic and sediment bacteria was amino acid transport and metabolism, which was active in different seasons.

Artificial consortium demonstrates emergent properties of enhanced cellulosic-sugar degradation and biofuel synthesis.

Planktonic cultures, of a rationally designed consortium, demonstrated emergent properties that exceeded the sums of monoculture properties, including a >200% increase in cellobiose catabolism, a >100% increase in glycerol catabolism, a >800% increase in ethanol production, and a >120% increase in biomass productivity. The consortium was designed to have a primary and secondary-resource specialist that used crossfeeding with a positive feedback mechanism, division of labor, and nutrient and energy transfer via necromass catabolism. The primary resource specialist was Clostridium phytofermentans (a.k.a. Lachnoclostridium phytofermentans), a cellulolytic, obligate anaerobe. The secondary-resource specialist was Escherichia coli, a versatile, facultative anaerobe, which can ferment glycerol and byproducts of cellobiose catabolism. The consortium also demonstrated emergent properties of enhanced biomass accumulation when grown as biofilms, which created high cell density communities with gradients of species along the vertical axis. Consortium biofilms were robust to oxic perturbations with E. coli consuming O2, creating an anoxic environment for C. phytofermentans. Anoxic/oxic cycling further enhanced biomass productivity of the biofilm consortium, increasing biomass accumulation ~250% over the sum of the monoculture biofilms. Consortium emergent properties were credited to several synergistic mechanisms. E. coli consumed inhibitory byproducts from cellobiose catabolism, driving higher C. phytofermentans growth and higher cellulolytic enzyme production, which in turn provided more substrate for E. coli. E. coli necromass enhanced C. phytofermentans growth while C. phytofermentans necromass aided E. coli growth via the release of peptides and amino acids, respectively. In aggregate, temporal cycling of necromass constituents increased flux of cellulose-derived resources through the consortium. The study establishes a consortia-based, bioprocessing strategy built on naturally occurring interactions for improved conversion of cellulose-derived sugars into bioproducts.

Biofilm dynamics: linking in situ biofilm biomass and metabolic activity measurements in real-time under continuous flow conditions.

The tools used to study biofilms generally involve either destructive, end-point analyses or periodic measurements. The advent of the internet of things (IoT) era allows circumvention of these limitations. Here we introduce and detail the development of the BioSpec; a modular, nondestructive, real-time monitoring system, which accurately and reliably track changes in biofilm biomass over time. The performance of the system was validated using a commercial spectrophotometer and produced comparable results for variations in planktonic and sessile biomass. BioSpec was combined with the previously developed carbon dioxide evolution measurement system (CEMS) to allow simultaneous measurement of biofilm biomass and metabolic activity and revealed a differential response of these interrelated parameters to changing environmental conditions. The application of this system can facilitate a greater understanding of biofilm mass-function relationships and aid in the development of biofilm control strategies.

Sequencing effort dictates gene discovery in marine microbial metagenomes.

Massive metagenomic sequencing combined with gene prediction methods were previously used to compile the gene catalogue of the ocean and host-associated microbes. Global expeditions conducted over the past 15 years have sampled the ocean to build a catalogue of genes from pelagic microbes. Here we undertook a large sequencing effort of a perturbed Red Sea plankton community to uncover that the rate of gene discovery increases continuously with sequencing effort, with no indication that the retrieved 2.83 million non-redundant (complete) genes predicted from the experiment represented a nearly complete inventory of the genes present in the sampled community (i.e., no evidence of saturation). The underlying reason is the Pareto-like distribution of the abundance of genes in the plankton community, resulting in a very long tail of millions of genes present at remarkably low abundances, which can only be retrieved through massive sequencing. Microbial metagenomic projects retrieve a variable number of unique genes per Tera base-pair (Tbp), with a median value of 14.7 million unique genes per Tbp sequenced across projects. The increase in the rate of gene discovery in microbial metagenomes with sequencing effort implies that there is ample room for new gene discovery in further ocean and holobiont sequencing studies.

Increased Antibacterial and Antibiofilm Properties of Silver Nanoparticles Using Silver Fluoride as Precursor.

Silver nanoparticles were produced with AgF as the starting Ag(I) salt, with pectin as the reductant and protecting agent. While the obtained nanoparticles (pAgNP-F) have the same dimensional and physicochemical properties as those already described by us and obtained from AgNO3 and pectin (pAgNP-N), the silver nanoparticles from AgF display an increased antibacterial activity against E. coli PHL628 and Staphylococcus epidermidis RP62A (S. epidermidis RP62A), both as planktonic strains and as their biofilms with respect to pAgNP-N. In particular, a comparison of the antimicrobial and antibiofilm action of pAgNP-F has been carried out with pAgNP-N, pAgNP-N and added NaF, pure AgNO3, pure AgF, AgNO3 and added NaF and pure NaNO3 and NaF salts. By also measuring the concentration of the Ag+ cation released by pAgNP-F and pAgNP-N, we were able to unravel the separate contributions of each potential antibacterial agent, observing an evident synergy between p-AgNP and the F- anion: the F- anion increases the antibacterial power of the p-AgNP solutions even when F- is just 10 µM, a concentration at which F- alone (i.e., as its Na+ salt) is completely ineffective.

Photodynamic inactivation mediated by 5-aminolevulinic acid of bacteria in planktonic and biofilm forms.

Bacterial photodynamic inactivation (PDI) employing endogenous production of porphyrins from 5-aminolevulinic acid (ALA) - named ALA-PDI-, is a new promising tool to achieve bacteria control in non-spread infections. The technique combines the action of the porphyrins acting as photosensitisers with light, to produce reactive oxygen species to target the pathogen. To date, some clinical applications of ALA-PDI have been reported although variable responses ranging from total eradication to absence of photokilling were found. ALA-PDI conducted at suboptimal conditions may lead to misleading results and the complexity of haem synthesis in bacteria hinders the optimization of the treatment. The present work aimed to gain insight on the variables affecting ALA-PDI in Gram-positives and Gram-negatives bacteria growing on planktonic and biofilm cultures and to correlate the degree of the response with the amount and type of porphyrin synthesised. Staphylococcus epidermidis and Escherichia coli clinical isolates and Pseudomonas aeruginosa ATCC27853 and Staphylococcus aureus ATCC25923 strains were utilised, and the optimal conditions of concentration and time exposure of ALA, and light dose were set. In both Gram-positive species analysed, a peak of porphyrin synthesis was observed at 1-2 mM ALA in biofilm and planktonic cultures, which fairly correlated with the decrease in the number of CFU after PDI (5 to 7 logs) and porphyrin content was in the same order of magnitude. In addition, ALA-PDI was similarly effective for planktonic and biofilm S. aureus cultures, and more effective in S. epidermidis planktonic cultures at low light doses. Beyond a certain light dose, it was not possible to achieve further photosensitization. Similarly, a plateau of cell death was attained at a certain ALA incubation time. Accumulation of hydrophilic porphyrins at longer incubation periods was observed. The proportion of porphyrins changed as a function of ALA concentration and incubation time in the Gram-positive bacteria, though we did not find a clear correlation between the porphyrin type and PDI response. As a salient feature was the presence of isococroporphyrin isoforms in both Gram-positive and Gram-negative bacteria. Gram-negative bacteria were quite refractory to the treatment: P. aeruginosa was slightly inactivated (4-logs reduction) at 40 mM ALA, whereas E. coli was not inactivated at all. These species accumulated high ALA quantities and the amount of porphyrins did not correlate with the degree of photoinactivation. Our microscopy studies show that porphyrins are not located in the envelopes of Gram-negative bacteria, reinforcing the hypothesis that endogenous porphyrins fail to attack these structures.

Darunavir inhibits Cryptococcus neoformans/Cryptococcus gattii species complex growth and increases the susceptibility of biofilms to antifungal drugs.

Introduction. Cryptococcus species are pathogens commonly associated with cases of meningoencephalitis in individuals who are immunosuppressed due to AIDS.Aim. The aim was to evaluate the effects of the antiretroviral darunavir alone or associated with fluconazole, 5-flucytosine and amphotericin B against planktonic cells and biofilms of Cryptococcus species.Methodology. Susceptibility testing of darunavir and the common antifungals against 12 members of the Cryptococcus neoformans/Cryptococcus gattii species complex was evaluated by broth microdilution. The interaction between darunavir and antifungals against planktonic cells was tested by a checkerboard assay. The effects of darunavir against biofilm metabolic activity and biomass were evaluated by the XTT reduction assay and crystal violet staining, respectively.Results. Darunavir combined with amphotericin B showed a synergistic interaction against planktonic cells. No antagonistic interaction was observed between darunavir and the antifungals used. All Cryptococcus species strains were strong biofilm producers. Darunavir alone reduced biofilm metabolic activity and biomass when added during and after biofilm formation (P<0.05). The combination of darunavir with antifungals caused a significant reduction in biofilm metabolic activity and biomass when compared to darunavir alone (P<0.05).Conclusion. Darunavir presents antifungal activity against planktonic cells of Cryptococcus species and synergism with amphotericin B. In addition, darunavir led to reduced biofilm formation and showed activity against mature biofilms of Cryptococcus species. Activity of the antifungals against mature biofilms was enhanced in the presence of darunavir.

Prolonged inhibitory effects against planktonic growth, adherence, and biofilm formation of pathogens causing ventilator-associated pneumonia using a novel polyamide/silver nanoparticle composite-coated endotracheal tube.

Microbial cells can rapidly form biofilm on endotracheal tubes (ETT) causing ventilator-associated pneumonia, a serious complication in patients receiving mechanical ventilation. A novel polyamide with a good balance of hydrophilic/hydrophobic moieties was used for the embedment of green-reduction silver nanoparticles (AgNPs) for the composite-coated ETT. The films were conformal with a thickness of ∼ 17 ± 3 µm accommodating high loading of 60 ± 35 nm spherical-shaped AgNPs. The coated ETT resulted in a significant difference in reducing both planktonic growth and microbial adhesion of single and mixed-species cultures, compared with uncoated ETT (p < 0.05). A time-kill assay demonstrated rapid bactericidal effects of the coating on bacterial growth and cell adhesion to ETT surface. Biofilm formation by Pseudomonas aeruginosa and Staphylococcus aureus, commonly encountered pathogens, was inhibited by > 96% after incubation for 72 h. Polyamide/AgNP composite-coated ETT provided a broad-spectrum activity against both Gram-positive and Gram-negative bacteria as well as Candida albicans and prolonged antimicrobial activity.

Genetic and virulence characterisation of Vibrio parahaemolyticus isolated from Indian coast.

BACKGROUND: V. parahaemolyticus is autochthonous to the marine environment and causes seafood-borne gastroenteritis in humans. Generally, V. parahaemolyticus recovered from the environment and/or seafood is thought to be non-pathogenic and the relationship between environmental isolates and acute diarrhoeal disease is poorly understood. In this study, we explored the virulence potential of environmental V. parahaemolyticus isolated from water, plankton and assorted seafood samples collected from the Indian coast. RESULTS: Twenty-two V. parahaemolyticus isolates from seafood harboured virulence associated genes encoding the thermostable-direct haemolysin (TDH), TDH-related haemolysin (TRH), and Type 3 secretion systems (T3SS) and 95.5% of the toxigenic isolates had pandemic strain attributes (toxRS/new+). Nine serovars, with pandemic strain traits were newly identified and an O4:K36 tdh-trh+V. parahaemolyticus bearing pandemic marker gene was recognised for the first time. Results obtained by reverse transcription PCR showed trh, T3SS1 and T3SS2ß to be functional in the seafood isolates. Moreover, the environmental strains were cytotoxic and could invade Caco-2 cells upon infection as well as induce changes to the tight junction protein, ZO-1 and the actin cytoskeleton. CONCLUSION: Our study provides evidence that environmental isolates of V. parahaemolyticus are potentially invasive and capable of eliciting pathogenic characteristics typical of clinical strains and present a potential health risk. We also demonstrate that virulence of this pathogen is highly complex and hence draws attention for the need to investigate more reliable virulence markers in order to distinguish the environmental and clinical isolates, which will be crucial for the pathogenomics and control of this pathogen.

Metatranscriptomic identification of polyamine-transforming bacterioplankton in the Gulf of Mexico.

The importance of short-chained aliphatic polyamines (PAs) to bacterioplankton-mediated carbon and nitrogen cycles has been repeatedly proposed. However, bacterial taxa and genes involved in the transformations of different PA compounds and their potential spatial variations remain unclear. This study collected surface bacterioplankton from nearshore, offshore, and open ocean stations in the Gulf of Mexico and examined how metatranscriptomes responded to additions of three single PA model compounds (i.e. putrescine, spermidine, or spermine). Our data showed an overrepresentation of genes affiliated with γ-glutamylation and spermidine cleavage pathways in metatranscriptomes received PA amendments and the expression level of each pathway varied among different PA compounds and sampling locations. PA-transforming taxa were affiliated with Actinobacteria, Bacteroidetes, Cyanobacteria, Planctomycetes, and Proteobacteria and their relative importance was also compound and location specific. These findings suggest that PAs are transformed via multiple pathways and by a diversity of marine bacterioplankton in the Gulf of Mexico. The relative importance of different PA transforming pathways and composition of functional microbial communities may be regulated by nutrient status of local environments.

In vitro activity of the antimicrobial peptide AP7121 against the human methicillin-resistant biofilm producers Staphylococcus aureus and Staphylococcus epidermidis.

In vitro activity against methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis biofilm producers from blood cultures of patients with prosthetic hip infections was evaluated. The Minimum Inhibitory Concentration (MIC) for AP7121 was determined and the bactericidal activity of AP7121 (MICx1, MICx4) against planktonic cells was studied at 4, 8 and 24 h. The biofilms formed were incubated with AP7121 (MICx1, MICx4) for 1 and 24 h. The anti-adhesion effect of an AP7121-treated inert surface over the highest MIC isolate was studied with scanning electron microscopy (SEM). The bactericidal activity of AP7121 against all the planktonic staphylococcal cells was observed at 4 h at both peptide concentrations. Dose-dependent anti-biofilm activity was detected. AP7121 (MICx4) showed bactericidal activity at 24 h in all isolates. SEM confirmed prevention of biofilm formation. This research showed the in vitro anti-biofilm activity of AP7121 against MRSA and S. epidermidis and the prevention of biofilm formation by them on an abiotic surface.