Physiological and Biochemical Characterization of Isolated Bacteria from a Coccolithophore Chrysotila dentata (Prymnesiophyceae) Culture

Coccolithophores are involved in oceanic carbon and nitrogen cycles, and they also have an impact on global climate change. Chrysotila dentata have a complex and close relationship with phycosphere bacteria. In this study, culturable phycosphere bacteria (free-living bacteria and attached bacteria) are isolated from C. dentata by a gradient dilution method and identified based on the 16S rRNA gene sequencing analysis. The phylogenetic tree (neighbor-joining tree, N-J tree) was constructed using the bacterial sequences and closest related sequences from GenBank. Colony characteristics, Gram nature, and physiological and biochemical characteristics were obtained based on a series of tests, such as the sugar utilization (glucose, arabinose, xylose, maltose, and mannitol) test, Voges–Proskauer reaction, urease tests, gelatin liquefaction, Gram test, starch hydrolysis, among others. In this study, seven strains (CF1, CF2, CF3, CF5, CF6, and CF7) of free-living bacteria (CF) and five strains (CA1, CA2, CA3, CA4, and CA5) of attached bacteria (CA) are isolated and identified. We found that the culturable phycosphere bacteria of C. dentata were mainly α-proteobacteria and γ-proteobacteria, with a small part of the CFB (Cytophaga-Flexibacter-Bacteroides) group bacteria and firmicutes. In this study, most α-proteobacteria can utilize malonate and positive in the urease test, meanwhile they can grow in a 7% NaCl medium. Differently to α-proteobacteria, γ-proteobacteria are more reactive, and can utilize maltose, glucose, arabinose, malonate, aesculin, and starch hydrolysis. Meanwhile, γ-proteobacteria can growth in a 7% NaCl and pH 5.7 medium, and some bacteria of this strain were positive in nitrate reduction. Firmicutes are similar to γ-proteobacteria: they are similar in reactivity, as they can utilize maltose, glucose, arabinose, malonate, aesculin, and starch hydrolysis, and can growth in a 7% NaCl and pH 5.7 medium. The difference is that some of firmicutes were positive in gelatin liquefaction and can utilize mannitol. The CFB group of bacteria were only positive in malonate, aesculin, and starch hydrolysis. The above results provide basic experimental data for further studies on the relationship between the coccolithophores and culturable phycosphere bacteria.

Use of Stress Signals of Their Attached Bacteria to Monitor Sympagic Algae Preservation in Canadian Arctic Sediments

Based on the strong aggregation of sympagic (ice-associated) algae and the high mortality or inactivity of bacteria attached to them, it was previously hypothesized that sympagic algae should be significant contributors to the export of carbon to Arctic sediments. In the present work, the lipid content of 30 sediment samples collected in the Canadian Arctic was investigated to test this hypothesis. The detection of high proportions of trans vaccenic fatty acid (resulting from cis-trans isomerase (CTI) activity of bacteria under hypersaline conditions) and 10S-hydroxyhexadec-8(trans)-enoic acid (resulting from 10S-DOX bacterial detoxification activity in the presence of deleterious free palmitoleic acid) confirmed: (i) the strong contribution of sympagic material to some Arctic sediments, and (ii) the impaired physiological status of its associated bacterial communities. Unlike terrestrial material, sympagic algae that had escaped zooplanktonic grazing appeared relatively preserved from biotic degradation in Arctic sediments. The expected reduction in sea ice cover resulting from global warming should cause a shift in the relative contributions of ice-associated vs. pelagic algae to the seafloor, and thus to a strong modification of the carbon cycle.

Diel Protein Regulation of Marine Picoplanktonic Communities Assessed by Metaproteomics

The diel cycle is of enormous biological importance in that it imposes temporal structure on ecosystem productivity. In the world’s oceans, microorganisms form complex communities that carry out about half of photosynthesis and the bulk of life-sustaining nutrient cycling. How the functioning of microbial communities is impacted by day and night periods in surface seawater remains to be elucidated. In this study, we compared the day and night metaproteomes of the free-living and the particle-attached bacterial fractions from picoplanktonic communities sampled from the northwest Mediterranean Sea surface. Our results showed similar taxonomic distribution of free-living and particle-attached bacterial populations, with Alphaproteobacteria, Gammaproteobacteria and Cyanobacteria being the most active members. Comparison of the day and night metaproteomes revealed that free-living and particle-attached bacteria were more active during the day and the night, respectively. Interestingly, protein diel variations were observed in the photoautotroph Synechococcales and in (photo)-heterotrophic bacteria such as Flavobacteriales, Pelagibacterales and Rhodobacterales. Moreover, our data demonstrated that diel cycle impacts light-dependent processes such as photosynthesis and UV-stress response in Synechococcales and Rhodobacterales, respectively, while the protein regulation from the ubiquitous Pelagibacterales remained stable over time. This study unravels, for the first time, the diel variation in the protein expression of major free-living and particle-attached microbial players at the sea surface, totaling an analysis of eight metaproteomes.

Effect of N-Acetylcysteine in Combination with Antibiotics on the Biofilms of Three Cystic Fibrosis Pathogens of Emerging Importance

Cystic fibrosis (CF) is a genetic disorder causing dysfunctional ion transport resulting in accumulation of viscous mucus that fosters chronic bacterial biofilm-associated infection in the airways. Achromobacter xylosoxidans and Stenotrophomonas maltophilia are increasingly prevalent CF pathogens and while Burkholderia cencocepacia is slowly decreasing; all are complicated by multidrug resistance that is enhanced by biofilm formation. This study investigates potential synergy between the antibiotics ciprofloxacin (0.5–128 µg/mL), colistin (0.5–128 µg/mL) and tobramycin (0.5–128 µg/mL) when combined with the neutral pH form of N-Acetylcysteine (NACneutral) (0.5–16.3 mg/mL) against 11 cystic fibrosis strains of Burkholderia, Stenotrophomonas and Achromobacter sp. in planktonic and biofilm cultures. We screened for potential synergism using checkerboard assays from which fraction inhibitory concentration indices (FICI) were calculated. Synergistic (FICI ≤ 0.5) and additive (0.5 > FICI ≥ 1) combinations were tested on irreversibly attached bacteria and 48 h mature biofilms via time-course and colony forming units (CFU/mL) assays. This study suggests that planktonic FICI analysis does not necessarily translate to reduction in bacterial loads in a biofilm model. Future directions include refining synergy testing and determining further mechanisms of action of NAC to understand how it may interact with antibiotics to better predict synergy.

Effects of Pre-Treatment Using Plasma on the Antibacterial Activity of Mushroom Surfaces

Although non-thermal atmospheric pressure plasma is an efficient tool for preventing post-harvest microbial contamination, many studies have focused on the post-treatment of infected or contaminated foods. In this study, we examined the antimicrobial quality of mushrooms pre-treated with a non-thermal atmospheric pressure plasma jet (NTAPPJ) or plasma-treated water (PTW). The CFU (Colony Forming Unit) number of Escherichia coli inoculated on surfaces of mushrooms pre-treated with NTAPPJ or PTW was significantly reduced (about 60–75% for NTAPPJ and about 35–85% for PTW), and the reduction rate was proportional to the treatment time. Bacterial attachment and viability of the attached bacteria were decreased on NTAPPJ-treated mushroom surfaces. This may be caused by the increased hydrophilicity and oxidizing capacity observed on NTAPPJ-treated mushroom surfaces. In PTW-treated mushrooms, bacterial attachment was not significantly changed, but death and lipid peroxidation of the attached bacteria were significantly increased. Analysis of mushroom quality showed that loss of water content was greater in mushrooms treated with NTAPPJ compared to that in those with no treatment (control) and PTW treatment during storage. Our results suggest that pre-treatment with NTAPPJ or PTW can improve the antibacterial quality of mushroom surfaces by decreasing bacterial attachment (for NTAPPJ) and increasing bacterial lipid peroxidation (for both NTAPPJ and PTW).

Assessment of a Weak Mode of Bacterial Adhesion by Applying an Electric Field

Microbial attachment to surfaces is ubiquitous in nature. Most species of bacteria attach and adhere to surfaces via special appendages such as pili and fimbriae, the roles of which have been extensively studied. Here, we report an experiment on pilus-less mutants of Caulobacter crescentus weakly attached to polyethylene surface. We find that some individual cells transiently but repeatedly adhere to the surface in a stick-slip fashion in the presence of an electric field parallel to the surface. These bacteria move significantly slower than the unattached ones in the same field of view undergoing electrophoretic motion. We refer this behavior of repeated and transient attachment as “quasi-attachment”. The speed of the quasi-attached bacteria exhibits large variation, frequently dropping close to zero for short intervals of time. We propose a polymeric tethering model to account for the experimental findings. This study sheds light on bacteria–surface interaction, which is significant in broader contexts such as infection and environmental control.

Dynamics of Free-Living and Attached Bacterial Assemblages in Skeletonema sp. Diatom Cultures at Elevated Temperatures

In the context of global warming, changes in phytoplankton-associated bacterial communities have the potential to change biogeochemical cycling and food webs in marine ecosystems. Skeletonema is a cosmopolitan diatom genus in coastal waters worldwide. Here, we grew a Skeletonema strain with its native bacterial assemblage at different temperatures and examined cell concentrations of Skeletonema sp. and free-living bacteria, dissolved organic carbon (DOC) concentrations of cultures, and the community structure of both free-living and attached bacteria at different culture stages. The results showed that elevated temperature increased the specific growth rates of both Skeletonema and free-living bacteria. Different growth stages had a more pronounced effect on community structure compared with temperatures and different physical states of bacteria. The effects of temperature on the structure of the free-living bacterial community were more pronounced compared with diatom-attached bacteria. Carbon metabolism genes and those for some specific amino acid pathways were found to be positively correlated with elevated temperature, which may have profound implications on the oceanic carbon cycle and the marine microbial loop. Network analysis revealed evidence of enhanced cooperation with an increase in positive interactions among different bacteria at elevated temperature. This may help the whole community to overcome the stress of elevated temperature. We speculate that different bacterial species may build more integrated networks with a modified functional profile of the whole community to cope with elevated temperature. This study contributes to an improved understanding of the response of diatom-associated bacterial communities to elevated temperature.

Bacterial community composition of the sea grape Caulerpa lentillifera: a comparison between healthy and diseased states

The bacterial communities of the sea grape Caulerpa lentillifera were studied during a disease outbreak in Vietnam. The Rhodobacteraceae and Rhodovulum dominated the composition of healthy C. lentillifera. Clear differences between healthy and diseased cases were observed at order, genus and Operational Taxonomic Unit (OTU) level. Bacterial diversity was lower in healthy C. lentillifera, probably because of antimicrobial compounds from the macroalgae and/or from Clostridium, Cutibacterium or Micrococcus bacteria. The likely beneficial role of Bradyrhizobium, Paracoccus and Brevundimonas strains on nutrient cycling and phytohormone production was discussed. The white coloration of diseased C. lentillifera may not only be associated with pathogens but also with an oxidative response. Aquibacter, Winogradskyella and other OTUs of the family Flavobacteriaceae were hypothesized as detrimental bacteria, this family comprises some well-known seaweed pathogens. Moreover, Thalassobius OTU 2935 and 1635 may represent detrimental Rhodobacteraceae. Phycisphaera together with other Planctomycetes and Woeseia were probably saprophytes of C. lentillifera. This study offers pioneering insights on the co-occurrence of C. lentillifera-attached bacteria, potential detrimental or beneficial microbes, and a baseline for understanding the C. lentillifera holobiont. Further metagenomic and biotechnological approaches are needed to confirm functions of some microbes on this macroalgae to enhance food security in the tropics.

Strategies for Interfering With Bacterial Early Stage Biofilms

Biofilm-related bacteria show high resistance to antimicrobial treatments, posing a remarkable challenge to human health. Given bacterial dormancy and high expression of efflux pumps, persistent infections caused by mature biofilms are not easy to treat, thereby driving researchers toward the discovery of many anti-biofilm molecules that can intervene in early stage biofilms formation to inhibit further development and maturity. Compared with mature biofilms, early stage biofilms have fragile structures, vigorous metabolisms, and early attached bacteria are higher susceptibility to antimicrobials. Thus, removing biofilms at the early stage has evident advantages. Many reviews on anti-biofilm compounds that prevent biofilms formation have already been done, but most of them are based on compound classifications to introduce anti-biofilm effects. This review discusses the inhibitory effects of anti-biofilm compounds on early stage biofilms formation from the perspective of the mechanisms of action, including hindering reversible adhesion, reducing extracellular polymeric substances production, interfering in the quorum sensing, and modifying cyclic di-GMP. This information can be exploited further to help researchers in designing new molecules with anti-biofilm activity.