Min Cao | Clemson University (original) (raw)

Papers by Min Cao

Molecular Microbiology, 2002

Bacillus subtilis encodes seven extracytoplasmic function (ECF) sigma factors. The sigma(W) regul... more Bacillus subtilis encodes seven extracytoplasmic function (ECF) sigma factors. The sigma(W) regulon includes functions involved in detoxification and protection against antimicrobials, whereas sigma(M) is essential for growth at high salt concentrations. We now report that antibiotics that inhibit cell wall biosynthesis induce both sigma(W) and sigma(M) regulons as monitored using DNA microarrays. Induction of selected sigma(W)-dependent genes was confirmed using lacZ reporter fusions and Northern blot analysis. The ability of vancomycin to induce the sigma(W) regulon is dependent on both sigma(W) and the cognate anti-sigma, RsiW, but is independent of the transition state regulator AbrB. These results suggest that the membrane-localized RsiW anti-sigma(W) factor mediates the transcriptional response to cell wall stress. Our findings are consistent with the idea that one function of ECF sigma factors is to coordinate antibiosis stress responses and cell envelope homeostasis.

Journal of Molecular Biology, 2002

The Bacillus subtilis extracytoplasmic function (ECF) sigma factor sigma(W) controls a large regu... more The Bacillus subtilis extracytoplasmic function (ECF) sigma factor sigma(W) controls a large regulon that is strongly induced by alkali shock. To define the physiological role of sigma(W) we have sought to identify the complete set of genes under sigma(W) control. Previously, we described a promoter consensus search procedure to identify sigma(W) controlled genes. Herein, we introduce a novel method to identify additional target promoters: run-off transcription followed by macroarray analysis (ROMA). We compare the resulting list of targets with those identified in conventional transcriptional profiling studies and using the consensus search approach. While transcriptional profiling identifies genes that are strongly dependent on sigma(W) for in vivo expression, some sigma(W)-dependent promoters are not detected due to the masking effects of other promoter elements, overlapping recognition with other ECF sigma factors, or both. Taken together, the consensus search, ROMA, and transcriptional profiling approaches establish a minimum of 30 promoter sites (controlling approximately 60 genes) as direct targets for activation by sigma(W). Significantly, no single approach identifies more than approximately 80% of the regulon so defined. We therefore suggest that a combination of two or more complementary approaches be employed in studies seeking to achieve maximal coverage when defining bacterial regulons. Our results indicate that sigma(W) controls genes that protect the cell against agents that impair cell wall biosynthesis but fail to reveal any connection to operons likely to function in adaptation to alkaline growth conditions. This is consistent with the observation that a sigW mutant is unaffected in its ability to survive alkali shock. We conclude that in B. subtilis sudden imposition of alkali stress activates the sigma(W) stress response, perhaps by impairing the ability of the cell wall biosynthetic machinery to function.

Journal of Bacteriology, 2003

The Bacillus subtilis extracytoplasmic function sigma factor σ Y is of unknown function. We demon... more The Bacillus subtilis extracytoplasmic function sigma factor σ Y is of unknown function. We demonstrate that the sigY operon is expressed from an autoregulatory promoter site, P Y . We selected for transposon-induced mutations that upregulate P Y transcription in an attempt to identify genes involved in σ Y regulation. The resulting insertions disrupted yxlC , the gene immediately downstream of sigY . However, the phenotype of the yxlC ::Tn 10 insertion was due to polarity on the downstream genes of the sigY operon; a nonpolar insertion in yxlC did not lead to derepression of P Y . Further analyses revealed that both yxlD and yxlE encoded proteins important for the negative regulation of σ Y activity. A comparison of the transcriptomes of wild-type and yxlC ::Tn 10 mutant strains revealed elevated expression of several operons. However, only one additional gene, ybgB , was unambiguously identified as a direct target for σ Y . This was supported by analysis of direct targets for σ Y ...

Microbiology, 2003

Copper ions induce expression of the Bacillus subtilis copZA operon encoding a metallochaperone, ... more Copper ions induce expression of the Bacillus subtilis copZA operon encoding a metallochaperone, CopZ, and a CPx-type ATPase efflux protein, CopA. The copZA promoter region contains an inverted repeat sequence similar to that recognized by the mercury-sensing MerR protein. To investigate the possible involvement of MerR homologues in copZA regulation, null mutations were engineered affecting each of four putative MerR-type regulators: yyaN, yraB, yfmP and yhdQ. Two of these genes affected copper regulation. Mutation of yhdQ (hereafter renamed cueR) dramatically reduced copper induction of copZA, and purified CueR bound with high affinity to the copZA promoter region. These results suggest that CueR is a direct regulator of copZA transcription that mediates copper induction. Surprisingly, a yfmP mutation also reduced copper induction of copZA. Sequence analysis suggested that yfmP was cotranscribed with yfmO, encoding a putative multidrug efflux protein. The yfmPO operon is autoregul...

PLoS ONE, 2014

Botanicals are rich in bioactive compounds, and some offer numerous beneficial effects to animal ... more Botanicals are rich in bioactive compounds, and some offer numerous beneficial effects to animal and human health when consumed. It is well known that phytochemicals in cranberries have anti-oxidative and antimicrobial activities. Recently, an increasing body of evidence has demonstrated that cranberry phytochemicals may have potential benefits that promote healthy aging. Here, we use Caenorhabditis elegans as a model to show that water-soluble cranberry extract standardized to 4.0% proanthocyanidins (WCESP), a major component of cranberries, can enhance host innate immunity to resist against Vibrio cholerae (V. cholerae; wild type C6706 (O1 El Tor biotype)) infection. Supplementation of WCESP did not significantly alter the intestinal colonization of V. cholerae, but upregulated the expression of C. elegans innate immune genes, such as clec-46, clec-71, fmo-2, pqn-5 and C23G10.1. Additionally, WCESP treatment did not affect the growth of V. cholerae and expression of the major bacterial virulence genes, and only slightly reduced bacterial colonization within C. elegans intestine. These findings indicate that the major components of WCESP, including proanthocyanidins (PACs), may play an important role in enhancing the host innate immunity. Moreover, we engaged C. elegans mutants and identified that the p38 MAPK signaling, insulin/IGF-1 signaling (IIS), and HSF-1 play pivotal roles in the WCESP-mediated host immune response. Considering the level of conservation between the innate immune pathways of C. elegans and humans, the results of this study suggest that WCESP may also play an immunity-promoting role in higher order organisms.

Methods in Molecular Biology, 2013

The principle of commonly used methods to create mutations in the nematode Caenorhabditis elegans... more The principle of commonly used methods to create mutations in the nematode Caenorhabditis elegans (C. elegans) is straightforward. In general, worms are exposed to a dose of mutagen resulting in DNA damages and mutations. Screening the progeny of the mutagenized animals for a certain phenotype is the regular forward genetic approach in C. elegans. A mutant selected from such a population is stabilized to recover a pure homozygous strain. In this chapter, we categorize the protocol into mutagenesis, phenotype screen, and outcross and provide time-tested procedures for their implementation to create long-lived worm mutants.

Bacillus subtilis sigM null mutant, lacking the extracytoplasmic function M protein, was sensitiv... more Bacillus subtilis sigM null mutant, lacking the extracytoplasmic function M protein, was sensitive to paraquat (PQ), a superoxide-generating reagent, but not to the redox stress-inducing compounds hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide, or diamide. Surprisingly, a sigM mutant was only sensitive to superoxide-generating compounds with a dipyridyl ring such as PQ, ethyl viologen, benzyl viologen, and diquat but not to menadione, plumbagin, pyrogallol, or nitrofurantoin. Mutational analysis of candidate M-regulated genes revealed that both YqjL, a putative hydrolase, and BcrC, a bacitracin resistance protein, were involved in PQ resistance. Expression of yqjL, but not bcrC, from a xylose-inducible promoter restored PQ resistance to the sigM mutant.

Applied and environmental …, 2007

In this study, we developed a new mariner-based transposition system for Listeria monocytogenes. ... more In this study, we developed a new mariner-based transposition system for Listeria monocytogenes. The mariner-based system has a high rate of transposition and a low rate of plasmid retention, and transposition is very random, making it an ideal tool for high-throughput transposon mutagenesis in L. monocytogenes. Listeria monocytogenes is a saprophytic gram-positive bacterial rod that is ubiquitous in nature and is an opportunistic foodborne pathogen of humans and a variety of other vertebrates (24). During infection, L. monocytogenes multiplies intracellularly in the cytosols of host cells (19, 23). Intracellular survival of L. monocytogenes relies largely on its ability to subvert host functions by escaping phagocytic vacuoles and spreading from cell to cell without exiting the intracellular milieu. In the last two decades, multiple studies have aimed at identifying virulence factors and deciphering the mechanisms by which L. monocytogenes survives in a wide range of environments (9, 13). One of the most valuable genetic tools used to study bacteria is the transposon. Transposons can be used to perform high-throughput mutagenesis of an entire chromosome, generating banks of mutants that can be screened for identification of factors related to specific bacterial functions. The transposon delivery systems that are currently available for use with L. monocytogenes are not ideal for these types of studies (4, 7, 14). For example, the most

Listeria monocytogenes is an intracellular bacterial pathogen whose virulence depends on the regu... more Listeria monocytogenes is an intracellular bacterial pathogen whose virulence depends on the regulated expression of numerous secreted bacterial factors. As for other gram-positive bacteria, many proteins secreted by L. monocytogenes are translocated across the bacterial membrane in an unfolded state to the compartment existing between the membrane and the cell wall. This compartment presents a challenging environment for protein folding due to its high density of negative charge, high concentrations of cations, and low pH. We recently identified PrsA2 as a gene product required for L. monocytogenes virulence. PrsA2 was identified based on its increased secretion by strains containing a mutationally activated form of prfA, the key regulator of L. monocytogenes virulence gene expression. The prsA2 gene product is one of at least two predicted peptidyl-prolyl cis/trans-isomerases encoded by L. monocytogenes; these proteins function as posttranslocation protein chaperones and/or foldases. In this study, we demonstrate that PrsA2 plays a unique and important role in L. monocytogenes pathogenesis by promoting the activity and stability of at least two critical secreted virulence factors: listeriolysin O (LLO) and a broad-specificity phospholipase. Loss of PrsA2 activity severely attenuated virulence in mice and impaired bacterial cell-to-cell spread in host cells. In contrast, mutants lacking prsA1 resembled wild-type bacteria with respect to intracellular growth and cell-to-cell spread as well as virulence in mice. PrsA2 is thus distinct from PrsA1 in its unique requirement for the stability and full activity of L. monocytogenes-secreted factors that contribute to host infection.

PLoS ONE, 2018

Quorum sensing (QS) and nucleotide-based second messengers are vital signaling systems that regul... more Quorum sensing (QS) and nucleotide-based second messengers are vital signaling systems that regulate bacterial physiology in response to changing environments. Disrupting bacterial signal transduction is a promising direction to combat infectious diseases, and QS and the second messengers are undoubtedly potential targets. In Vibrio cholerae, both QS and the second messenger 3', 5'-cyclic diguanylate (c-di-GMP) play a central role in controlling motility, motile-to-sessile life transition, and virulence. In this study, we found that water-soluble extract from the North American cranberry could significantly inhibit V. cho-lerae biofilm formation during the development/maturation stage by reducing the biofilm matrix production and secretion. The anti-biofilm effect by water-soluble cranberry extract was possibly through modulating the intracellular c-di-GMP level and was independent of QS and the QS master regulator HapR. Our results suggest an opportunity to explore more functional foods to fight stubborn infections through interference with the bacterial signaling systems.

Carbohydrate Polymers, 2018

This paper was the first to study extracellular polymeric substances (EPSs) of Thraustochytrium s... more This paper was the first to study extracellular polymeric substances (EPSs) of Thraustochytrium striatum on composition, structure and bioactivities. Two strains of T. striatum including original (ori) and high-biomass (mut) strains (induced by high-nitrogen stress) were compared. The EPSs from both strains mainly contained polysaccharide (41-64%, w/w, dry basis) and protein (25-40%, w/w, dry basis), which was shown by the morphology study with an AFM. The monosaccharide profile of the EPS polysaccharide was consisted of glucose, galactose, arabinose, and trace amount of xylose. Glucose and arabinose took up to 82-90% (w/w, dry basis) of the total polysaccharide. The structure and functional groups of EPSs were determined by FTIR and NMR. The NMR results revealed that the major structural linkages of the polysaccharides of both ori and mut EPSs were 1 → 6-β-glucan and 1 → 4-α-galactan branched with L-α-arabinose. The EPSs were found to have anti-tumor activities against mouse melanoma B16-F0, human prostate carcinoma DU145, human cervical carcinoma HeLa, and human lung carcinoma A549. The EPSs also showed antioxidant and anti-inflammatory activities and an-tibacterial activity against Pseudomonas aeruginosa.

Oncotarget, 2016

Numerous studies have demonstrated that dietary intervention may promote health and help prevent ... more Numerous studies have demonstrated that dietary intervention may promote health and help prevent Alzheimer's disease (AD). We recently reported that bee products of royal jelly (RJ) and enzyme-treated royal jelly (eRJ) were potent to promote healthy aging in C. elegans. Here, we examined whether RJ/eRJ consumption may benefit to mitigate the AD symptom in the disease model of C. elegans. Our results showed that RJ/eRJ supplementation significantly delayed the body paralysis in AD worms, suggesting the β-amyloid (Aβ) toxicity attenuation effects of RJ/eRJ. Genetic analyses suggested that RJ/eRJ-mediated alleviation of Aβ toxicity in AD worms required DAF-16, rather than HSF-1 and SKN-1, in an insulin/IGF signaling dependent manner. Moreover, RJ/eRJ modulated the transactivity of DAF-16 and dramatically improved the protein solubility in aged worms. Given protein solubility is a hallmark of healthy proteostasis, our findings demonstrated that RJ/eRJ supplementation improved proteostasis, and this promotion depended on the transactivity of DAF-16. Collectively, the present study not only elucidated the possible anti-AD mechanism of RJ/eRJ, but also provided evidence from a practical point of view to shed light on the extensive correlation of proteostasis and the prevention of neurodegenerative disorders.

Journals of Gerontology: Biological Sciences, 2015

A growing body of evidence suggests that nutraceuticals with prolongevity properties may delay th... more A growing body of evidence suggests that nutraceuticals with prolongevity properties may delay the onset of Alzheimer's disease (AD). We recently demonstrated that a proanthocyanidins-standardized cranberry extract has properties that prolong life span and promote innate immunity in Caenorhabditis elegans. In this article, we report that supplementation of this cranberry extract delayed Aβ toxicity-triggered body paralysis in the C elegans AD model. Genetic analyses indicated that the cranberry-mediated Aβ toxicity alleviation required heat shock transcription factor (HSF)-1 rather than DAF-16 and SKN-1. Moreover, cranberry supplementation increased the transactivity of HSF-1 in an IIS-dependent manner. Further studies found that the cranberry extract relies on HSF-1 to significantly enhance the solubility of proteins in aged worms, implying an improved proteostasis in AD worms. Considering that HSF-1 plays a pivotal role in maintaining proteostasis, our results suggest that cranberry maintains the function of proteostasis through HSF-1, thereby protecting C elegans against Aβ toxicity. Together, our findings elucidated the mechanism whereby cranberry attenuated Aβ toxicity in C elegans and stressed the significance of proteostasis in the prevention of age-related diseases from a practical point of view.

Recent studies suggest that royal jelly (RJ) and its related substances may have antiaging proper... more Recent studies suggest that royal jelly (RJ) and its related substances may have antiaging properties. However, the molecular mechanisms underlying the beneficial effects remain elusive. We report that the effects of RJ and enzyme-treated RJ (eRJ) on life span and health span in Caenorhabditis elegans (C elegans) are modulated by the sophisticated interplays of DAF-16, SIR-2.1, HCF-1, and 14-3-3 proteins. Dietary supplementation with RJ or eRJ increased C. elegans life span in a dose-dependent manner. The RJ and eRJ consumption increased the tolerance of C elegans to oxidative stress, ultraviolet irradiation, and heat shock stress. Our genetic analyses showed that RJ/eRJ-mediated life-span extension requires insulin/IGF-1 signaling and the activities of DAF-16, SIR-2.1, HCF-1, and FTT-2, a 14-3-3 protein. Earlier studies reported that DAF-16/FOXO, SIR-2.1/SIRT1, FTT-2, and HCF-1 have extensive interplays in worms and mammals. Our present findings suggest that RJ/eRJ-mediated promotion of longevity and stress resistance in C elegans is dependent on these conserved interplays. From an evolutionary point of view, this study not only provides new insights into the molecular mechanisms of RJ's action on health span promotion in C elegans, but also has imperative implications in using RJ/ eRJ as nutraceuticals to delay aging and age-related disorders.

Consumption of nutraceuticals is a major and potent dietary intervention for delaying aging. As t... more Consumption of nutraceuticals is a major and potent dietary intervention for delaying aging. As the timing of administration is critical for the efficacy of bioactive compounds in medicine, the effectiveness of nutraceuticals may also be dramatically affected by the timing of supplementation. Cranberry exact (CBE), rich in polyphenols, is consumed as a nutraceutical, and possesses anti-aging properties. Here, we examined the influence of timing on the beneficial effects of CBE supplementation in C. elegans. The prolongevity effect of CBE in different aged worms, young adults, middle-age adults, and aged adults, was determined. Early-start intervention with CBE prolonged the remaining lifespan of worms of different ages more robustly than late-start intervention. The effectiveness of CBE on stress responses and physiological behaviors in different aged worms was also investigated. The early-start intervention prominently promoted motility and resistance to heat shocks and V. cholera infection, especially in aged worms. Together, these findings suggest that the timing of CBE supplementation critically influences its

Aging is a complex and inevitable biological process that is associated with numerous chronically... more Aging is a complex and inevitable biological process that is associated with numerous chronically debilitating health effects. Development of effective interventions for promoting healthy aging is an active but challenging area of research. Mechanistic studies in various model organisms, noticeably two invertebrates, Caenorhabditis elegans and Drosophila melanogaster, have identified many genes and pathways as well as dietary interventions that modulate lifespan and healthspan. These studies have shed light on some of the mechanisms involved in aging processes and provide valuable guidance for developing efficacious aging interventions. Nutraceuticals made from various plants contain a significant amount of phytochemicals with diverse biological activities. Phytochemicals can modulate many signaling pathways that exert numerous health benefits, such as reducing cancer incidence and inflammation, and promoting healthy aging. In this paper, we outline the current progress in aging intervention studies using nutraceuticals from an evolutionary perspective in invertebrate models.

Listeria monocytogenes is the etiologic agent of listeriosis, a food-borne disease affecting huma... more Listeria monocytogenes is the etiologic agent of listeriosis, a food-borne disease affecting humans and a variety of animals. In order to combat this pathogen, it is crucial to have an understanding of its natural interplay with the environment. For this reason, the free soil nematode Caenorhabditis elegans was focused upon because of its shared natural habitat with Listeria and its potential as a model organism for Listeria pathogenesis. Previous studies have generated some contradictory results on Listeria's ability to kill C. elegans, making additional interaction studies such as this more attractive. In our study, we carried out a series of killing assays in a systematic manner using different Listeria strains under different growth conditions. In addition to studying the effects of planktonic cells, we examined the interaction between C. elegans and sessile listerial cells. Our findings suggest that, rather than causing infection and death, L. monocytogenes may extend the life span of C. elegans. This indicates that Listeria is not pathogenic to C. elegans. We also found that C. elegans can feed and ingest sessile cells, as well as carry the pathogen in its gut, implying that C. elegans could be a vehicle for L. monocytogenes spread in the environment.