The regulator CdsS/CdsR two-component system modulates expression of genes involved in chitin degradation of Pseudoalteromonas piscicida strain O-7

A pathway for chitin oxidation in marine bacteria

Oxidative degradation of chitin, initiated by lytic polysaccharide monooxygenases (LPMOs), contributes to microbial bioconversion of crystalline chitin, the second most abundant biopolymer in nature. However, our knowledge of oxidative chitin utilization pathways, beyond LPMOs, is very limited. Here, we describe a complete pathway for oxidative chitin degradation and its regulation in a marine bacterium, Pseudoalteromonas prydzensis. The pathway starts with LPMO-mediated extracellular breakdown of chitin into C1-oxidized chitooligosaccharides, which carry a terminal 2-(acetylamino)-2-deoxy-D-gluconic acid (GlcNAc1A). Transmembrane transport of oxidized chitooligosaccharides is followed by their hydrolysis in the periplasm, releasing GlcNAc1A, which is catabolized in the cytoplasm. This pathway differs from the known hydrolytic chitin utilization pathway in enzymes, transporters and regulators. In particular, GlcNAc1A is converted to 2-keto-3-deoxygluconate 6-phosphate, acetate and NH₃ via a series of reactions resembling the degradation of D-amino acids rather than other monosaccharides. Furthermore, genomic and metagenomic analyses suggest that the chitin oxidative utilization pathway may be prevalent in marine Gammaproteobacteria.

Microbial Surface Colonization and Biofilm Development in Marine Environments

Biotic and abiotic surfaces in marine waters are rapidly colonized by microorganisms. Surface colonization and subsequent biofilm formation and development provide numerous advantages to these organisms and support critical ecological and biogeochemical functions in the changing marine environment. Microbial surface association also contributes to deleterious effects such as biofouling, biocorrosion, and the persistence and transmission of harmful or pathogenic microorganisms and their genetic determinants. The processes and mechanisms of colonization as well as key players among the surface-associated microbiota have been studied for several decades. Accumulating evidence indicates that specific cell-surface, cell-cell, and interpopulation interactions shape the composition, structure, spatiotemporal dynamics, and functions of surface-associated microbial communities. Several key microbial processes and mechanisms, including (i) surface, population, and community sensing and signaling, (ii) intraspecies and interspecies communication and interaction, and (iii) the regulatory balance between cooperation and competition, have been identified as critical for the microbial surface association lifestyle. In this review, recent progress in the study of marine microbial surface colonization and biofilm development is synthesized and discussed. Major gaps in our knowledge remain. We pose questions for targeted investigation of surface-specific community-level microbial features, answers to which would advance our understanding of surface-associated microbial community ecology and the biogeochemical functions of these communities at levels from molecular mechanistic details through systems biological integration.

Chitinolytic microorganisms and their possible application in environmental protection

This paper provides a review of the latest research findings on the applications of microbial chitinases to biological control. Microorganisms producing these enzymes can inhibit the growth of many fungal diseases that pose a serious threat to global crop production. Currently, efforts are being made to discover producers of chitinolytic enzymes. The potential exists that natural biofungicides will replace chemical fungicides or will be used to supplement currently used fungicides, which would reduce the negative impact of chemicals on the environment and support the sustainable development of agriculture and forestry.

The Bacillus subtilis mannose regulator, ManR, a DNA-binding protein regulated by HPr and its cognate PTS transporter ManP

The transcriptional activator ManR of the Bacillus subtilis mannose utilization operon is composed of an N-terminal DNA-binding domain, two phosphotransferase system (PTS) regulation domains (PRDs), an EIIB(Bgl) - and an EIIA(Fru) -like domain. Site-specific mutagenesis of ManR revealed the role of conserved amino acids representing potential phosphorylation sites. This was investigated by β-galactosidase activity tests and by mobility shift assays after incubation with the PTS components HPr and EI. In analogy to other PRD-containing regulators we propose stimulation of ManR activity by phosphorylation. Mutations in PRD1 lowered ManR activity, whereas mutations in PRD2 abolished ManR activity completely. The Cys415Ala (EIIB(Bgl)) and the His570Ala mutations (EIIA(Fru)) provoked constitutive activities to different degrees, whereas the latter had the greater influence. Addition of EIIBA(Man) reduced the binding capability significantly in a wild-type and a Cys415Ala background, but had no effect on a His570Ala mutant. The different expression levels originating from the two promoters PmanR and PmanP could be ascribed to different 5'-untranslated mRNA regions. Sequences of 44 bp were identified and confirmed as the ManR binding sites by DNase I footprinting. The binding properties of ManR, in particular the equilibrium dissociation constant KD and the dissociation rate kdiss, were determined for both promoter regions.

[Regulation of chitinase genes expression in bacteria]

Chitinases, which can hydrolyze chitin, occur in a wide range of microorganisms including viruses, bacteria, and fungi. The derivatives of chitin are potentially useful in several areas such as food processing, medicines, and biological control in agriculture. Some bacteria can uptake and utilize chitin as carbon source by secreting chitinase. The chitin is degraded into chito-oligosaccharides [(GlcNAc)n] or N-acetylglucosamine (GlcNAc) by chitinases, and then the chitin derivatives are transferred into cells by specific transport systems of bacteria. The intracellular chitin derivatives activate or suppress the transcription of a series of chi genes and affect the amount of chitinase. The expression of chitinase genes are strictly regulated by various regulatory factors and responsive cis-acting elements. The present review will focus on the transport system and the regulation of chitinase genes expression in bacteria.

The importance of chitin in the marine environment

Chitin is the most abundant renewable polymer in the oceans and is an important source of carbon and nitrogen for marine organisms. The process of chitin degradation is a key step in the cycling of nutrients in the oceans and chitinolytic bacteria play a significant role in this process. These bacteria are autochthonous to both marine and freshwater ecosystems and produce chitinases that degrade chitin, an insoluble polysaccharide, to a biologically useful form. In this brief review, a description of the structure of chitin and diversity of chitinolytic bacteria in the oceans is provided, in the context of the significance of chitin degradation for marine life.

Analysis of the Pseudoalteromonas tunicata genome reveals properties of a surface-associated life style in the marine environment

BACKGROUND

Colonisation of sessile eukaryotic host surfaces (e.g. invertebrates and seaweeds) by bacteria is common in the marine environment and is expected to create significant inter-species competition and other interactions. The bacterium Pseudoalteromonas tunicata is a successful competitor on marine surfaces owing primarily to its ability to produce a number of inhibitory molecules. As such P. tunicata has become a model organism for the studies into processes of surface colonisation and eukaryotic host-bacteria interactions.

METHODOLOGY/PRINCIPAL FINDINGS

To gain a broader understanding into the adaptation to a surface-associated life-style, we have sequenced and analysed the genome of P. tunicata and compared it to the genomes of closely related strains. We found that the P. tunicata genome contains several genes and gene clusters that are involved in the production of inhibitory compounds against surface competitors and secondary colonisers. Features of P. tunicata's oxidative stress response, iron scavenging and nutrient acquisition show that the organism is well adapted to high-density communities on surfaces. Variation of the P. tunicata genome is suggested by several landmarks of genetic rearrangements and mobile genetic elements (e.g. transposons, CRISPRs, phage). Surface attachment is likely to be mediated by curli, novel pili, a number of extracellular polymers and potentially other unexpected cell surface proteins. The P. tunicata genome also shows a utilisation pattern of extracellular polymers that would avoid a degradation of its recognised hosts, while potentially causing detrimental effects on other host types. In addition, the prevalence of recognised virulence genes suggests that P. tunicata has the potential for pathogenic interactions.

CONCLUSIONS/SIGNIFICANCE

The genome analysis has revealed several physiological features that would provide P. tunciata with competitive advantage against other members of the surface-associated community. We have also identified properties that could mediate interactions with surfaces other than its currently recognised hosts. This together with the detection of known virulence genes leads to the hypothesis that P. tunicata maintains a carefully regulated balance between beneficial and detrimental interactions with a range of host surfaces.