Unexpected differential metabolic responses of Campylobacter jejuni to the abundant presence of glutamate and fucose

Introduction: Campylobacter jejuni is the leading cause of foodborne bacterial enteritis in humans, and yet little is known in regard to how genetic diversity and metabolic capabilities among isolates affect their metabolic phenotype and pathogenicity. Objectives: For instance, the C. jejuni 11168 strain can utilize both l-fucose and l-glutamate as a carbon source, which provides the strain with a competitive advantage in some environments and in this study we set out to assess the metabolic response of C. jejuni 11168 to the presence of l-fucose and l-glutamate in the growth medium. Methods: To achieve this, untargeted hydrophilic liquid chromatography coupled to mass spectrometry was used to obtain metabolite profiles of supernatant extracts obtained at three different time points up to 24 h. Results: This study identified both the depletion and the production and subsequent release of a multitude of expected and unexpected metabolites during the growth of C. jejuni 11168 under three different conditions. A large set of standards allowed identification of a number of metabolites. Further mass spectrometry fragmentation analysis allowed the additional annotation of substrate-specific metabolites. The results show that C. jejuni 11168 upon l-fucose addition indeed produces degradation products of the fucose pathway. Furthermore, methionine was faster depleted from the medium, consistent with previously-observed methionine auxotrophy. Conclusions: Moreover, a multitude of not previously annotated metabolites in C. jejuni were found to be increased specifically upon l-fucose addition. These metabolites may well play a role in the pathogenicity of this C. jejuni strain.</p

Comparison of genomes and proteomes of four whole genome-sequenced <i>Campylobacter jejuni</i> from different phylogenetic backgrounds

<div><p>Whole genome sequencing (WGS) has been used to assess the phylogenetic relationships, virulence and metabolic differences, and the relationship between gene carriage and host or niche differentiation among populations of <i>C</i>. <i>jejuni</i> isolates. We previously characterized the presence and expression of CJIE4 prophage proteins in four <i>C</i>. <i>jejuni</i> isolates using WGS and comparative proteomics analysis, but the isolates were not assessed further. In this study we compare the closed, finished genome sequences of these isolates to the total proteome. Genomes of the four isolates differ in phage content and location, plasmid content, capsular polysaccharide biosynthesis loci, a type VI secretion system, orientation of the ~92 kb invertible element, and allelic differences. Proteins with 99% sequence identity can be differentiated using isobaric tags for relative and absolute quantification (iTRAQ) comparative proteomic methods. GO enrichment analysis and the type of artefacts produced in comparative proteomic analysis depend on whether proteins are encoded in only one isolate or common to all isolates, whether different isolates have different alleles of the proteins analyzed, whether conserved and variable regions are both present in the protein group analyzed, and on how the analysis is done. Several proteins encoded by genes with very high levels of sequence identity in all four isolates exhibited preferentially higher protein expression in only one of the four isolates, suggesting differential regulation among the isolates. It is possible to analyze comparative protein expression in more distantly related isolates in the context of WGS data, though the results are more complex to interpret than when isolates are clonal or very closely related. Comparative proteomic analysis produced log₂ fold expression data suggestive of regulatory differences among isolates, indicating that it may be useful as a hypothesis generation exercise to identify regulated proteins and regulatory pathways for more detailed analysis.</p></div

Catchment land use and trophic state impacts on phytoplankton composition: a case study from the Rotorua lakes’ district, New Zealand

Trophic state of lakes has been related to catchment land use, but direct links between phytoplankton taxa and land use are limited. Phytoplankton composition, represented by relative cell abundance of phyla, was measured over a period of 4 years in 11 lakes in the Rotorua region, New Zealand. The lakes differed in morphometry, trophic state and land use (as percentage catchment area). We tested whether relative proportion of land uses, indirectly representing relative nutrient loading, was the overarching driver of phytoplankton composition. Trophic state was correlated negatively with native forest and positively with pasture and urban area. Cyanoprokaryota were correlated negatively with native forest and positively with pasture and trophic state, Chlorophyta were correlated positively with native forest and urban land use and negatively with pasture and trophic state, and Bacillariophyta were positively correlated with dissolved reactive silica to dissolved inorganic nitrogen (Si:DIN) and Si to dissolved reactive phosphorus (Si:DRP) ratios. Lakes with higher nutrient loads had higher trophic state and Cyanoprokaryota dominance. Chlorophyta were negatively correlated with Cyanoprokaryota and Bacillariophyta, suggesting competition amongst these groups. Our results apply to lakes potentially subject to changes in catchment land use, which may have implications for trophic state, phytoplankton composition and Cyanoprokaryota blooms