Influence of growth rate and nutrient limitation on monobactam production and peptidoglycan synthesis in Pseudomonas aeruginosa

Transcriptomic profiling of adding cobalt chloride to improve dendrobine-type total alkaloid production

Trichoderma longibrachiatum UN32 is known for its efficient production of dendrobine-type total alkaloids (DTTAs). This study aimed to determine the optimal medium composition for the UN32 strain using response surface methodology. Key factors, including glucose, beef extract, and CoCl2, were selected through the Plackett-Burman design. Subsequently, a factorial optimization approach was employed using the steepest ascent design, and 17 trial sets were completed via the Box-Behnken design. The optimal medium composition was found to consist of 29.4 g/L of glucose, 17.3 g/L of beef extract, and 0.28 mmol/L of CoCl2. This optimized medium resulted in an impressive 80.8% increase in mycelial dry weight (reaching 12.303 g/L) and a substantial 76.4% boost in DTTA production (reaching 541.63 ± 46.95 μg). Furthermore, the fermentation process was scaled up to a 5-L bioreactor, leading to a DTTA production approximately 1.95 times than the control. Transcriptome analysis of strain UN32 in response to CoCl2 supplementation revealed significant changes in the expression of critical genes associated with the TCA cycle and L-valine, L-leucine, and L-isoleucine biosynthesis changed. These alterations resulted in a heightened influx of acetyl-CoA into DTTA production. Additionally, the expression of genes related to antioxidant enzymes was modified to maintain homeostasis of reactive oxygen species (ROS). A potential mechanism for the accumulation of DTTAs based on ROS as a signal transduction was proposed. These findings provide valuable insights into the regulatory mechanisms of DTTA biosynthesis, potentially offering a method to enhance the production of secondary metabolites in the UN32 strain. KEY POINTS: • After the RSM optimization, there is a substantial increase of 80.8% in biomass production and a significant 76.4% rise in DTTA production. • Transcriptome analysis revealed that the inclusion of CoCl2 supplements resulted in an enhanced influx of acetyl-CoA. • Proposed a mechanism for the accumulation of DTTAs for the role of ROS as a signal transduction pathway.

RNASeq Based Transcriptional Profiling of Pseudomonas aeruginosa PA14 after Short- and Long-Term Anoxic Cultivation in Synthetic Cystic Fibrosis Sputum Medium

The opportunistic human pathogen Pseudomonas aeruginosa can thrive under microaerophilic to anaerobic conditions in the lungs of cystic fibrosis patients. RNA_Seq based comparative RNA profiling of the clinical isolate PA14 cultured in synthetic cystic fibrosis medium was performed after planktonic growth (OD₆₀₀ = 2.0; P), 30 min after shift to anaerobiosis (A-30) and after anaerobic biofilm growth for 96h (B-96) with the aim to reveal differentially regulated functions impacting on sustained anoxic biofilm formation as well as on tolerance towards different antibiotics. Most notably, functions involved in sulfur metabolism were found to be up-regulated in B-96 cells when compared to A-30 cells. Based on the transcriptome studies a set of transposon mutants were screened, which revealed novel functions involved in anoxic biofilm growth.In addition, these studies revealed a decreased and an increased abundance of the oprD and the mexCD-oprJ operon transcripts, respectively, in B-96 cells, which may explain their increased tolerance towards meropenem and to antibiotics that are expelled by the MexCD-OprD efflux pump. The OprI protein has been implicated as a target for cationic antimicrobial peptides, such as SMAP-29. The transcriptome and subsequent Northern-blot analyses showed that the abundance of the oprI transcript encoding the OprI protein is strongly decreased in B-96 cells. However, follow up studies revealed that the susceptibility of a constructed PA14ΔoprI mutant towards SMAP-29 was indistinguishable from the parental wild-type strain, which questions OprI as a target for this antimicrobial peptide in strain PA14.

Effect of nutrient limitation on adhesion characteristics of Pseudomonas aeruginosa

Pseudomonas aeruginosa causes a variety of diseases in humans including lung and ocular infections. Infections of the cornea are usually associated with wearing contact lenses and can result in loss of vision. This study aimed to determine the effect of carbon or nitrogen limitation on the adhesion to contact lenses of a strain of Ps. aeruginosa isolated from contact lens-related corneal inflammation. Cells were grown in a continuous culture apparatus in varying levels of glucose or ammonia to effect nutrient limitation. Adhesion to contact lenses was measured as total counts and viable counts. The cell surface hydrophobicity and charge were measured using adhesion to surface-modified Sepharose. Changes in lipopolysaccharide were determined using 1D SDS-PAGE and changes in cell-surface proteins were measured using 2D gel electrophoresis. The more the cultures were nitrogen limited, the greater the increase in adhesion to unworn hydrogel contact lenses 0.3 x 10(3) - 2.2 x 10(3) cells/mm2 on Etafilon A lenses. Cells that were carbon limited showed a greater increase in adhesion to contact lenses when the lenses had been coated in artificial tears. It appeared that lipopolysaccharide may have been involved in the constitutive adhesion to unworn lenses that occurred during C-limitation, whereas changes in the outer membrane proteins contributed to the increased adhesion under nitrogen limitation, or the change in adhesion that occurred to carbon-limited cells using contact lenses coated in artificial tears. Nine cell-surface proteins appeared during nitrogen limitation with kDa/pI of 75/4.8, 4.9, 5.0; 62/5.6; 89/6.5; 38/6.4; 28/1.5; 18/6.4; 12/4.5. Any or all of these may have been involved in the increased adhesion and further experiments are underway to examine this possibility.

The effect of ultrasound on Escherichia coli viability

The effect of continuous-wave ultrasound on the viability of Escherichia coli HB101 was assessed using a 20 kHz ultrasonic processor. A standardised cell suspension of fixed concentration was used to investigate the influence of different physical and environmental conditions on ultrasound susceptibility. Cell viability decreased exponentially with time at different intensities of ultrasound. Increasing intensity caused a decrease in decimal reduction times. Loss of cell viability occurred primarily from the mechanical effects of ultrasound rather than free radical damage. E. coli susceptibility was also shown to vary with growth conditions, whereby cells cultivated either on agar or harvested from the stationary phase of liquid culture were significantly more susceptible to ultrasound than an equivalent population obtained from the exponential phase of liquid growth. The implication of these results is discussed in relation to the use of ultrasound as a novel means of bacterial transformation.