The Influence of pCO2 and Temperature on Gene Expression of Carbon and Nitrogen Pathways in Trichodesmium IMS101

Growth, protein amount, and activity levels of metabolic pathways in Trichodesmium are influenced by environmental changes such as elevated pCO2 and temperature. This study examines changes in the expression of essential metabolic genes in Trichodesmium grown under a matrix of pCO2 (400 and 900 µatm) and temperature (25 and 31°C). Using RT-qPCR, we studied 21 genes related to four metabolic functional groups: CO2 concentrating mechanism (bicA1, bicA2, ccmM, ccmK2, ccmK3, ndhF4, ndhD4, ndhL, chpX), energy metabolism (atpB, sod, prx, glcD), nitrogen metabolism (glnA, hetR, nifH), and inorganic carbon fixation and photosynthesis (rbcL, rca, psaB, psaC, psbA). nifH and most photosynthetic genes exhibited relatively high abundance and their expression was influenced by both environmental parameters. A two to three orders of magnitude increase was observed for glnA and hetR only when both pCO2 and temperature were elevated. CO2 concentrating mechanism genes were not affected by pCO2 and temperature and their expression levels were markedly lower than that of the nitrogen metabolism and photosynthetic genes. Many of the CO2 concentrating mechanism genes were co-expressed throughout the day. Our results demonstrate that in Trichodesmium, CO2 concentrating mechanism genes are constitutively expressed. Co-expression of genes from different functional groups were frequently observed during the first half of the photoperiod when oxygenic photosynthesis and N2 fixation take place, pointing at the tight and complex regulation of gene expression in Trichodesmium. Here we provide new data linking environmental changes of pCO2 and temperature to gene expression in Trichodesmium. Although gene expression indicates an active metabolic pathway, there is often an uncoupling between transcription and enzyme activity, such that transcript level cannot usually be directly extrapolated to metabolic activity

Comparative proteomic profiles of the marine cyanobacterium Trichodesmium erythraeum IMS101 under different nitrogen regimes

Trichodesmium is a marine filamentous diazotrophic cyanobacterium and an important contributor of "new" nitrogen in the oligotrophic surface waters of the tropical and sub-tropical oceans. It is unique in that it exclusively fixes N(2) at daytime, although it belongs to the non-heterocystous filamentous segment of the cyanobacterial radiation. Here we present the first quantitative proteomic analysis of Trichodesmium erythraeum IMS101 when grown under different nitrogen regimes using 2-DE/MALDI-TOF-MS. Addition of combined nitrogen (NO3-) prevented development of the morphological characteristics of the N(2)-fixing cell type (diazocytes), inhibited expression of the nitrogenase enzyme subunits and consequently N(2) fixation activity. The diazotrophic regime (N(2) versus NO3- cultures) elicited the differential expression of more than 100 proteins, which represented 13.5% of the separated proteins. Besides proteins directly related to N(2) fixation, proteins involved in the synthesis of reducing equivalents and the generation of a micro-oxic environment were strongly up-regulated, as was in particular Dps, a protein related to iron acquisition and potentially other vital cellular processes. In contrast, proteins involved in the S-adenosylmethionine (SAM) cycle, synthesis of amino acids and production of carbon skeletons for storage and synthesis of amino acids were suppressed. The data are discussed in the context of Trichodesmium's unusual N(2)-fixing physiology.Gustaf Sandh, Liang Ran, Linghua Xu, Gustav Sundqvist, Vincent Bulone, and Birgitta Bergma

USA300 methicillin-resistant Staphylococcus aureus in Stockholm, Sweden, from 2008 to 2016.

Methicillin-resistant Staphylococcus aureus (MRSA) USA300 isolates have been recognized globally, not only in community but also in healthcare settings. USA300 isolates were initially resistant only to methicillin, but resistance to non-β-lactams has emerged with time. To evaluate the prevalence and antimicrobial susceptibility of USA300 isolates in Stockholm, we conducted a nine-year retrospective study. Of 5359 consecutive MRSA cases in Stockholm, isolates from 285 cases were USA300 strains according to the pulsed-field gel electrophoresis pattern. Of these cases, repeated isolates with altered antibiotic resistance patterns were observed in six individuals. Therefore, antimicrobial susceptibility testing was performed on totally 291 isolates. To study the phylogenetic relatedness of isolates in transmission events and genomic resistance traits, 35 isolates were further studied by whole genome sequencing (WGS). The incidence of MRSA was increased from 17.6 per 100,000 inhabitants in 2008 to 37.3 per 100,000 inhabitants in 2016, while the proportion of USA300 cases declined from 6.6% in 2008 to 2.6% in 2016. Among the USA300 isolates, 73.5% were community-associated, 21.3% healthcare-associated, and 5.2% had unknown acquisition. The highest resistance rate among non-β-lactams was found in erythromycin (86%), followed by fluoroquinolones (68-69%). 57% of the isolates were resistant to both erythromycin and fluoroquinolone. Simultaneous resistance to four non-β-lactam antibiotic classes was found in six isolates. Four isolates were susceptible to all non-β-lactam antibiotics. Ceftaroline, daptomycin, linezolid, mupirocin, rifampicin, teicoplanin, telavancin, trimethoprim-sulfamethoxazole and vancomycin retained full activity in the study. WGS analysis indicated that isolates from an outbreak were phylogenetically closely related. In conclusion, USA300 MRSA isolates in Stockholm have neither been limited to the community setting, nor remained susceptible to non-β-lactam agents. WGS is becoming a useful tool in tracing transmission events. The results herein provide the most up-to-date and comprehensive information regarding status of USA300 strains in this geographic area