Proteolytic control of FixT by the Lon protease impacts FixLJ signaling in Caulobacter crescentus.

Responding to changes in oxygen levels is critical for aerobic microbes. In Caulobacter crescentus, low oxygen is sensed by the FixL-FixJ two-component system which induces multiple genes, including those involved in heme biosynthesis, to accommodate microaerobic conditions. The FixLJ inhibitor FixT is also induced under low oxygen conditions and is degraded by the Lon protease when the oxygen levels are sufficient, which together provides negative feedback proposed to adjust FixLJ signaling thresholds during changing conditions. Here, we address whether degradation of FixT by the Lon protease contributes to phenotypic defects associated with loss of Lon. We find that ∆lon strains are deficient in FixLJ-dependent heme biosynthesis, consistent with elevated FixT levels as deletion of fixT suppresses this defect. Transcriptomics validate this result as, along with heme biosynthesis, there is diminished expression of many FixL-activated genes in ∆lon. However, stabilization of FixT in ∆lon strains does not contribute to restoring any known Lon-related fitness defect, such as cell morphology defects or stress sensitivity. In fact, cells lacking both FixT and Lon are compromised in viability during growth in standard aerobic conditions. Our work highlights the complexity of protease-dependent regulation of transcription factors and explains the molecular basis of defective heme accumulation in Lon-deficient Caulobacter. IMPORTANCE: The Lon protease shapes protein quality control, signaling pathways, and stress responses in many bacteria species. Loss of Lon often results in multiple phenotypic consequences. In this work, we found a connection between the Lon protease and deficiencies in heme accumulation that then led to our finding of a global change in gene expression due in part to degradation of a regulator of the hypoxic response. However, loss of degradation of this regulator did not explain other phenotypes associated with Lon deficiencies demonstrating the complex and multiple pathways that this highly conserved protease can impact.

The flipped learning perception scale: A validity and reliability study.

This study aims to develop a scale to determine preservice science teachers' perceptions of flipped learning. The present study uses the survey design, a quantitative research method. For content validity, the authors created an item pool of 144 items based on the literature. After being checked by experts, the item pool dropped to 49 items for the five-point Likert-type draft scale. The current study has preferred cluster sampling due to generalization concerns. The accessible population of the study is the preservice science teachers in Türkiye's provinces of Kayseri, Nevsehir, Nigde, Kirsehir, and Konya. We administered the draft scale to 490 preservice science teachers, which is the recommended 10 times the number of items. We also performed explanatory and confirmatory factor analyses to check the scale's construct validity. We ultimately obtained a four-factor structure with 43 items that explain 49.2% of the variance in scores and found the correlation between the criterion and draft scales to be greater than .70, thus ensuring criterion validity. We calculated Cronbach's alpha and composite reliability coefficients to check the reliability of the scale and determined the reliability coefficients for both the overall scale and the sub-factors to be greater than 0.70. As a result, we have obtained a scale consisting of 43 items and four dimensions that explains 49.2% of the variance. This data collection tool can be used by researchers and lecturers to determine preservice teachers' perceptions toward flipped learning.

Proteolytic control of FixT by the Lon protease impacts FixLJ signaling in Caulobacter crescentus.

Responding to changes in oxygen levels is critical for aerobic microbes. In Caulobacter crescentus, low oxygen is sensed by the FixL-FixJ two-component system which induces multiple genes, including heme biosynthesis, to accommodate microaerobic conditions. The FixLJ inhibitor FixT is also induced under low oxygen conditions and is degraded by the Lon protease, which together provides negative feedback proposed to adjust FixLJ signaling thresholds during changing conditions. Here, we address if the degradation of FixT by the Lon protease contributes to phenotypic defects associated with loss of Lon. We find that ∆lon strains are deficient in FixLJ-dependent heme biosynthesis, consistent with elevated FixT levels as deletion of fixT suppresses this defect. Transcriptomics validate this result as there is diminished expression of many FixLJ-activated genes in ∆lon. However, no physiological changes in response to microaerobic conditions occurred upon loss of Lon, suggesting that FixT dynamics are not a major contributor to fitness in oxygen limiting conditions. Similarly, stabilization of FixT in ∆lon strains does not contribute to any known Lon-related fitness defect, such as cell morphology defects or stress sensitivity. In fact, cells lacking both FixT and Lon are compromised in viability during adaptation to long term aerobic growth. Our work highlights the complexity of protease-dependent regulation of transcription factors and explains the molecular basis of defective heme accumulation in Lon-deficient Caulobacter.