The Phagocytosis of Lacticaseibacillus casei and Its Immunomodulatory Properties on Human Monocyte-Derived Dendritic Cells Depend on the Expression of Lc-p75, a Bacterial Peptidoglycan Hydrolase.

The human gut symbiont Lacticaseibacillus (L.) casei (previously Lactobacillus casei) is under intense research due to its wide range of immunomodulatory effects on the human host. Dendritic cells (DCs) are crucial players in the direct and indirect communication with lactobacilli in the gastrointestinal tract. Here, we demonstrate that human monocyte-derived DCs (moDCs) are able to engulf L. casei BL23, in which the intact bacterial cell wall and morphology have a key role. The absence of the bacterial cell-wall-degrading enzyme, Lc-p75, in L. casei cells causes remarkable morphological changes, which have important consequences in the phagocytosis of L. casei by moDCs. Our results showed that the Lc-p75 mutation induced defective internalization and impaired proinflammatory and T-cell-polarizing cytokine secretion by bacteria-exposed moDCs. The T helper (Th) 1 and Th17 cell activating capacity of moDCs induced by the mutant L. casei was consequently reduced. Moreover, inhibition of the phagocytosis of wild-type bacteria showed similar results. Taken together, these data suggested that formation of short bacterial chains helps to exert the potent immunomodulatory properties of L. casei BL23.

Characterization of antibacterial activity of a N-acetylmuramoyl-L-alanine amidase produced by Latilactobacillus sakei isolated from salami.

Lactic acid bacteria are the predominant group within meat products, whose metabolites such as bacteriocins and peptidoglycan hydrolases inhibit pathogenic or spoilage bacteria. Fermented meat products, as a salami, is a good source to analyze the viable microbiota, due to these products present a low risk to consumer health. The aim of this work was to identify the lactic acid bacteria with broad antibacterial activity present in salami, purify the protein responsible for this activity, achieve antagonistic spectrum and perform the biochemical characterization. Five strains from salami were selected, isolated and identified by 16S rRNA gene sequencing. The antimicrobial activity was evaluated by antagonism assay and zymography, using spoilage microorganisms commonly found in meat products. The strain that showed a broad antibacterial activity was Latilactobacillus sakei and the antibacterial activity was given by a protein with 75-kDa of molecular mass, identified by LC/MALDI-TOF/TOF. The sequence analysis showed 67% of identity with a N-acetylmuramoyl-L-alanine amidase protein with five non-identical LysM domains. The purified protein showed an optimal pH of 8.0 and heat resistance at 80 °C for 10 min. L. sakei strain displayed antibacterial activity against Gram-negative and Gram-positive spoilage microorganisms. The results of this study provide the information to use Latilactobacillus sakei as a starter culture which will provide the necessary metabolites to combat undesirable microorganisms. Additionally, the conditions and properties for the best application and use of the antibacterial protein produced by this strain. This protein may have a potential use in the food industry as a new antibacterial agent.

Effect of subinhibitory concentrations of tigecycline and ciprofloxacin on the expression of biofilm-associated genes and biofilm structure of Staphylococcus epidermidis.

Staphylococcus epidermidis is a leading cause of foreign body-associated infections. This is related to the bacterium's ability to form biofilms on synthetic materials. Bacteria within a biofilm may be exposed to subinhibitory concentrations (sub-MICs) of antibiotics because of an agent's limited penetration into the biofilm core. Here, we investigated the effect of sub-MICs of tigecycline and ciprofloxacin on the expression of biofilm-associated genes, i.e. icaA, altE and sigB, and the biofilm structure of five clinical isolates of S. epidermidis. For most tested isolates, the expression of these genes increased after exposure to 0.25 MIC and 0.5 MIC tigecycline. A slight decrease in icaAmRNA levels was observed only in two isolates in the presence of 0.25 MIC tigecycline. The effect of ciprofloxacin exposure was isolate-dependent. At 0.5 MIC, ciprofloxacin induced an increase of sigB and icaAmRNA levels in three of the five tested isolates. At the same time, expression of the altE gene increased in all isolates (from 1.3-fold to 42-fold, depending on the strain). Confocal laser scanning microscopy analysis indicated that sub-MIC ciprofloxacin decreased biofilm formation, whereas tigecycline stimulated this process. Our data suggest that sub-MIC tigecycline may have bearing on the outcome of infections.

Antibiofilm Activities of a Novel Chimeolysin against Streptococcus mutans under Physiological and Cariogenic Conditions.

Streptococcus mutans often survives as a biofilm on the tooth surface and contributes to the development of dental caries. We investigated the efficacy of ClyR, an engineered chimeolysin, against S. mutans biofilms under physiological and cariogenic conditions. Susceptibility tests showed that ClyR was active against all clinical S. mutans isolates tested as well as S. mutans biofilms that displayed resistance to penicillin. The S. mutans biofilms that formed on hydroxyapatite discs under physiological sugar conditions and cariogenic conditions were reduced ∼2 logs and 3 logs after treatment with 100 µg/ml ClyR, respectively. In comparison, only a 1-log reduction was observed in the chlorhexidine gluconate (ChX)-treated group, and no killing effect was observed in the NaF-treated group. A mouse dental colonization model showed that repeated use of ClyR for 3 weeks (5 µg/day) reduced the number of colonized S. mutans cells in the dental plaques significantly (P < 0.05) and had no harmful effects on the mice. Furthermore, toxicity was not noted at concentrations exceeding those used for the in vitro and in vivo studies, and ClyR-specific antibodies could not be detected in mouse saliva after repeated use of ClyR in the oral cavity. Our data collectively demonstrate that ClyR is active against S. mutans biofilms both in vitro and in vivo, thus representing a preventative or therapeutic agent for use against dental caries.

A highly unstable transcript makes CwlO D,L-endopeptidase expression responsive to growth conditions in Bacillus subtilis.

The Bacillus subtilis cell wall is a dynamic structure, composed of peptidoglycan and teichoic acid, that is continually remodeled during growth. Remodeling is effected by the combined activities of penicillin binding proteins and autolysins that participate in the synthesis and turnover of peptidoglycan, respectively. It has been established that one or the other of the CwlO and LytE D,L-endopeptidase-type autolysins is essential for cell viability, a requirement that is fulfilled by coordinate control of their expression by WalRK and SigI RsgI. Here we report on the regulation of cwlO expression. The cwlO transcript is very unstable, with its degradation initiated by RNase Y cleavage within the 187-nucleotide leader sequence. An antisense cwlO transcript of heterogeneous length is expressed from a SigB promoter that has the potential to control cellular levels of cwlO RNA and protein under stress conditions. We discuss how a multiplicity of regulatory mechanisms makes CwlO expression and activity responsive to the prevailing growth conditions.

The WalRK (YycFG) and σ(I) RsgI regulators cooperate to control CwlO and LytE expression in exponentially growing and stressed Bacillus subtilis cells.

The WalRK (YycFG) two-component system co-ordinates cell wall metabolism with growth by regulating expression of autolysins and proteins that modulate autolysin activity. Here we extend its role in cell wall metabolism by showing that WalR binds to 22 chromosomal loci in vivo. Among the newly identified genes of the WalRK bindome are those that encode the wall-associated protein WapA, the penicillin binding proteins PbpH and Pbp5, the minor teichoic acid synthetic enzymes GgaAB and the regulators σ(I) RsgI. The putative WalR binding sequence at many newly identified binding loci deviates from the previously defined consensus. Moreover, expression of many newly identified operons is controlled by multiple regulators. An unusual feature is that WalR binds to an extended DNA region spanning multiple open reading frames at some loci. WalRK directly activates expression of the sigIrsgI operon from a newly identified σ(A) promoter and represses expression from the previously identified σ(I) promoter. We propose that this regulatory link between WalRK and σ(I) RsgI expression ensures that the endopeptidase requirement (CwlO or LytE) for cell viability is fulfilled during growth and under stress conditions. Thus the WalRK and σ(I) RsgI regulatory systems cooperate to control cell wall metabolism in growing and stressed cells.

Synthetic lethality of the lytE cwlO genotype in Bacillus subtilis is caused by lack of D,L-endopeptidase activity at the lateral cell wall.

Bacterial peptidoglycan acts as an exoskeleton to protect the bacterial cell. Although peptidoglycan biosynthesis by penicillin-binding proteins is well studied, few studies have described peptidoglycan disassembly, which is necessary for a dynamic structure that allows cell growth. In Bacillus subtilis, more than 35 genes encoding cell wall lytic enzymes have been identified; however, only two D,L-endopeptidases (lytE and cwlO) are involved in cell proliferation. In this study, we demonstrated that the D,L-endopeptidase activity at the lateral cell wall is essential for cell proliferation. Inactivation of LytE and CwlO by point mutation of the catalytic residues caused cell growth defects. However, the forced expression of LytF or CwlS, which are paralogs of LytE, did not suppress lytE cwlO synthetic lethality. Subcellular localization studies of these D,L-endopeptidases showed LytF and CwlS at the septa and poles, CwlO at the cylindrical part of the cell, and LytE at the septa and poles as well as the cylindrical part. Furthermore, construction of N-terminal and C-terminal domain-swapped enzymes of LytE, LytF, CwlS, and CwlO revealed that localization was dependent on the N-terminal domains. Only the chimeric proteins that were enzymatically active and localized to the sidewall were able to suppress the synthetic lethality, suggesting that the lack of D,L-endopeptidase activity at the cylindrical part of the cell leads to a growth defect. The functions of LytE and CwlO in cell morphogenesis were discussed.

Role of ArlRS in autolysis in methicillin-sensitive and methicillin-resistant Staphylococcus aureus strains.

Autolysis plays an essential role in bacterial cell division and lysis with ß-lactam antibiotics. Accordingly, the expression of autolysins is tightly regulated by several endogenous regulators, including ArlRS, a two component regulatory system that has been shown to negatively regulate autolysis in methicillin-sensitive Staphylococcus aureus (MSSA) strains. In this study, we found that inactivation of arlRS does not play a role in autolysis of methicillin-resistant S. aureus (MRSA) strains, such as community-acquired (CA)-MRSA strains USA300 and MW2 or the hospital-acquired (HA)-MRSA strain COL. This contrasts with MSSA strains, including Newman, SH1000, RN6390, and 8325-4, where autolysis is affected by ArlRS. We further demonstrated that the striking difference in the roles of arlRS between MSSA and MRSA strains is not due to the methicillin resistance determinant mecA. Among known autolysins and their regulators, we found that arlRS represses lytN, while no effect was seen on atl, lytM, and lytH expression in both CA- and HA-MRSA strains. Transcriptional-fusion assays showed that the agr transcripts, RNAII and RNAIII, were significantly more downregulated in the arlRS mutant of MW2 than the MSSA strain Newman. Importantly, provision of agr RNAIII in trans to the MW2 arlRS mutant via a multicopy plasmid induced autolysis in this MRSA strain. Also, the autolytic phenotype in the arlRS mutant of MSSA strain Newman could be rescued by a mutation in either atl or lytM. Together, these data showed that ArlRS impacts autolysis differently in MSSA and MRSA strains.

The CpxR/CpxA two-component system up-regulates two Tat-dependent peptidoglycan amidases to confer bacterial resistance to antimicrobial peptide.

We demonstrate that the twin arginine translocation (Tat) system contributes to bacterial resistance to cationic antimicrobial peptides (CAMPs). Our results show that a deletion at the tatC gene, which encodes a subunit of the Tat complex, caused Salmonella and Escherichia coli to become susceptible to protamine. We screened chromosomal loci that encode known and predicted Tat-dependent proteins and found that two N-acetylmuramoyl-l-alanine amidases, encoded by amiA and amiC, elevated bacterial resistance to protamine and α-helical peptides magainin 2 and melittin but not to ß-sheet defensin HNP-1 and lipopeptide polymyxin B. Genetic analysis suggests that transcription of both amiA and amiC loci in Salmonella is up-regulated by the CpxR/CpxA two-component system when nlpE is overexpressed. A footprinting analysis reveals that CpxR protein can interact with amiA and amiC promoters at the CpxR box, which is localized between the predicted -10 and -35 regions but present on different strands in these two genes. In addition, our results show that activation of the CpxR/CpxA system can facilitate protamine resistance because nlpE overexpression elevates this resistance in the wild-type strain but not the cpxR deletion mutant. Thus, we uncover a new transcriptional regulation pathway in which the Cpx envelope stress response system modulates the integrity of the cell envelope in part by controlling peptidoglycan amidase activity, which confers bacterial resistance to protamine and α-helical CAMPs. Our studies have important implications for understanding transcriptional regulation of peptidoglycan metabolism and also provide new insights into the role of the bacterial envelope in CAMP resistance.

Unveiling the expression characteristics of IspC, a cell wall-associated peptidoglycan hydrolase in Listeria monocytogenes, during growth under stress conditions.

Listeria monocytogenes serotype 4b is a food-borne pathogen of public health concern, since it accounts for approximately 40% of human listeriosis cases. We have recently identified IspC, a surface-localized peptidoglycan hydrolase, as the antigen recognized by a number of monoclonal antibodies (MAbs) produced against a serotype 4b strain for diagnostic applications. To determine whether IspC, which is well conserved among various serotype 4b strains, is a useful diagnostic marker in antibody-based methods, we assessed the expression of IspC in L. monocytogenes cultured under normal and stress conditions. A functional promoter directing the transcription of the ispC gene was identified upstream of the ispC open reading frame by constructing a promoterless lacZ gene fusion with the putative ispC promoter region and by 5' rapid amplification of cDNA ends analysis. Using both the lacZ reporter gene system and immunofluorescent staining with an IspC-specific MAb, we provide evidence that IspC is expressed on the cell surface in all growth conditions tested (temperature, osmotic stress, pH, ethanol, oxidative stress, anaerobic conditions, carbon source, and type of growth media) that allow for cellular division, although the level of ispC gene expression varies. These results demonstrated the usefulness of IspC as an excellent diagnostic marker for the serotype 4b strains and imply that IspC, in conjunction with specific MAbs, can be targeted for detection and isolation of L. monocytogenes serotype 4b strains directly from food, environmental, and clinical samples with minimal or no need for culture enrichment.

The sensitivity of Bacillus subtilis to diverse antimicrobial compounds is influenced by Abh.

Abh is a transition state regulator of Bacillus subtilis that controls biofilm formation and the production of several diverse antimicrobial compounds. Using a high-throughput non-biased technique, we show for the first time that Abh influences the sensitivity of B. subtilis to diverse antimicrobial compounds. Following up on these findings with a combination of classical genetics and antibiotic susceptibility assays, we demonstrate that Abh influences cellular processes such as the remodelling of the cell wall. We present data demonstrating that the extracytoplasmic function sigma factor σ(X) controls resistance to ß-lactam antibiotics by activating abh transcription. Downstream from Abh, activation of slrR expression by Abh is responsible for controlling the sensitivity of B. subtilis to such antibiotics due to the role that SlrR plays in regulating autolysin biosynthesis. The abh mutant additionally exhibits increased resistance to aminoglycoside antimicrobials. We confirm that aminoglycoside killing of B. subtilis is likely to be caused by oxidative damage but rule out the possibility that the increased resistance of the abh mutant to aminoglycosides is due to a general increase in resistance to oxidative stress.

Role of AmpD, OprF and penicillin-binding proteins in beta-lactam resistance in clinical isolates of Pseudomonas aeruginosa.

In this study, the mechanisms leading to increased chromosomal AmpC beta-lactamase expression and the contributory roles of the outer-membrane protein OprF and penicillin-binding proteins were analysed in 33 characterized clinical isolates of Pseudomonas aeruginosa. The genes ampD and ampE were analysed by PCR and DNA sequencing. Expression of the gene oprF was assessed using real-time RT-PCR, and penicillin-binding proteins were analysed using a chemiluminescence assay. Several of the isolates with increased ampC expression had major deletions affecting ampD, although in some isolates the mechanism of increased ampC expression could not be ascertained. Occasional isolates had increased expression of both ampC and oprF but remained susceptible to cephalosporins, suggesting that increased beta-lactamase activity could not offset increased outer-membrane permeability. There were no discernible changes in penicillin-binding proteins. Genomic deletions in ampD were observed in selected clinical isolates of P. aeruginosa with increased expression of the AmpC beta-lactamase. For some isolates, cephalosporin resistance was dependent upon the interplay of ampC and oprF expression.

Antibacterial metabolites and bacteriolytic enzymes produced by Bacillus pumilus during bacteriolysis of Arthrobacter citreus.

The marine isolate Bacillus pumilus SBUG 1800 is able to lyse living cells of Arthrobacter citreus on solid media as well as pasteurized A. citreus cells in liquid mineral salt medium. The cultivation of B. pumilus in the presence of pasteurized A. citreus is accompanied by an enhanced production of 2,5-diketopiperazines (DKPs). DKPs inhibit bacterial growth, but do not seem to cause bacteriolysis. This study shows that B. pumilus also lyses living cells of A. citreus in co-culture experiments as an intraguild predator, even if the inoculum of B. pumilus is low. In order to characterize the bacteriolytic process, more precisely changes in the extracellular metabolome and proteome have been analyzed under different culture conditions. Besides the known DKPs, a number of different pumilacidins and bacteriolytic enzymes are produced. Two lipopeptides with [M + H](+) = 1008 and [M + H](+) = 1022 were detected and are proposed to be pumilacidin H and I. While the lipopeptides lyse living bacterial cells in lysis test assays, a set of extracellular enzymes degrades the dead cell material. Two of the cell wall hydrolases involved have been identified as N-acetylmuramoyl-L-alanine amidase and beta-N-acetylglucosaminidase. These findings together with electron microscopic and cell growth monitoring during co-culture experiments give a detailed view on the bacteriolytic process.

Effect of the SinR protein on the expression of the Bacillus subtilis 168 lytABC operon.

Transcription of the lytABC operon was determined by extension of primers on RNAs isolated from strains bearing a deficient sinR gene. A SinR null mutant, in which part of the sinR gene was deleted, exhibits a pattern identical to that characteristic of FlaB (SigD) deficient mutants, i.e., loss of the signal corresponding to the SigD-dependent promoter, but not of that recognized by the SigA form of the RNA polymerase. However, strains bearing either flaD1 or flaD2, two different point mutations of gene sinR, were characterized by a complete loss of signals corresponding to both promoters. Thus, modified FlaD1 and FlaD2 proteins behave like a repressor affecting the expression of lytABC more severely than does the absence of SinR, The most obvious interpretation of this observation is a direct interaction between the SinR protein and the promoters recognized by the SigD form of the RNA polymerase.

Reconstruction and expression of the autolytic gene from Clostridium acetobutylicum ATCC 824 in Escherichia coli.

The complete lyc gene encoding the autolytic lysozyme of Clostridium acetobutylicum ATCC 824 was reconstructed from two overlapping DNA fragments and cloned into a suitable plasmid enabling Escherichia coli to produce this lytic enzyme under the control of the lac promoter. A polypeptide with an apparent M(r) of 35,000, corresponding to that predicted from the nucleotide sequence, was observed by maxicell analysis of whole-cell extracts of E. coli harboring the clostridial gene. The enzyme yield was shown to depend on the pH of the culture medium, since the protein was unstable at alkaline pH. The expression of the lyc gene was not increased by using the E. coli strong promoter, lpp-lac, probably due to the limit imposed by the extreme differences in codon usage. Although the LYC lysozyme does not contain a cleavable signal peptide, most of the protein was found in the periplasmic fraction of E. coli suggesting that this enzyme was secreted through a specific mechanism, as already observed for other autolysins.

The transcriptional signatures of Sodalis glossinidius in the Glossina palpalis gambiensis flies negative for Trypanosoma brucei gambiense contrast with those of this symbiont in tsetse flies positive for the parasite: possible involvement of a Sodalis-hosted prophage in fly Trypanosoma refractoriness?

Tsetse flies, such as Glossina palpalis gambiensis, are blood-feeding insects that could be subverted as hosts of the parasite Trypanosoma brucei gambiense: initiated in the tsetse fly mid gut, the developmental program of this parasite further proceeds in the salivary glands. The flies act as vectors of this human-invasive parasite when their salivary glands sustain the generation of metacyclic trypomastigotes, the exclusive morphotypes pre-programmed to further develop in the human individuals. Briefly, once the metacyclic trypomastigotes have been deposited in the skin of humans from whom the parasite-hosting tsetse flies are taking their blood meals, the complex developmental program of this Trypanosoma brucei subspecies can result in a severe disease named sleeping sickness. Unveiling the processes that could prevent, in tsetse flies, the developmental program of T. b. gambiense could contribute reducing the prevalence of the disease. Using a global approach, we were curious to extract transcriptional signatures of Sodalis glossinidius, a symbiont hosted by three distinct groups of tsetse flies. To meet this objective, the transcriptome of S. glossinidius from susceptible and refractory tsetse flies was analyzed at 3, 10 and 20 days after flies blood feed on T. b. gambiense-hosting mice. Within this temporal window, 176 trypanosome responsive genes were shown to interact in well-defined patterns making it possible to distinguish flies susceptible to the parasite infection from refractory flies. Among the modulated transcripts in the symbiont population of flies refractory to trypanosome infection many were shown to cluster within the following networks: "lysozyme activity, bacteriolytic enzyme, bacterial cytolysis, cell wall macromolecule catabolic process". These novel data are further delineated in the following questions: could the activation of prophage hosted by S. glossinidius lead to the release of bacterial agonists that trigger the tsetse fly immune system along a profile that no more allows the parasite developmental program?

The heat-inducible essential response regulator WalR positively regulates transcription of sigI, mreBH and lytE in Bacillus subtilis under heat stress.

The actin homolog MreBH governs cell morphogenesis of Bacillus subtilis through localization of the cell wall hydrolase LytE. The alternative sigma factor SigI of B. subtilis coordinately regulates transcription of mreBH and lytE. Transcription of sigI, mreBH and lytE is heat-inducible. The essential response regulator WalR (YycF) plays a key role in coordinating cell wall metabolism with cell proliferation. We now demonstrate that mreBH is a new member of the WalR regulon. We also found that WalR can positively and directly regulate sigI transcription under heat stress through a binding site located upstream of the σ(I) promoter of sigI. In addition, we found that a WalR binding site located upstream of the SigI binding site in the regulatory region of lytE is important for lytE expression under heat stress. Moreover, we found that walR is a new member of the heat shock stimulon of B. subtilis. WalR appears to coordinately and positively regulate transcription of sigI, mreBH and lytE under heat stress. Finally, our work shows for the first time that WalR can stimulate activities of σ(I) promoters under heat stress.

Production and purification of the bacterial autolysin N-acetylmuramoyl-L-alanine amidase B from Pseudomonas aeruginosa.

The bacterial cell wall heteropolymer peptidoglycan is not a static structure as it is constantly being made and recycled throughout the bacterium's life cycle. This turnover of peptidoglycan is a highly coordinated event involving a complement of autolytic enzymes that include those with specificity for either the carbohydrate or the peptide linkages of peptidoglycan. One major class of these autolysins are the N-acetylmuramoyl-L-alanine amidases which cleave the amide linkage between the stem peptides and the lactyl moiety of muramoyl residues. They are required in the periplasm for cell separation during division and in both the periplasm and cytoplasm to trim soluble released PG fragments during turnover for recycling. The gene encoding N-acetylmuramoyl-L-alanine amidase B in Pseudomonas aeruginosa was cloned and over-expressed in Escherichia coli. The recombinant protein with a C-terminal His-tag was purified to apparent homogeneity by a combination of affinity and cation-exchange chromatographies using Ni(2+)NTA-agarose and Source S, respectively. Four separate assays involving zymography, light scattering, HPLC and MALDI-TOF mass spectrometry were used to confirm the activity of the protein as an N-acetylmuramoyl-L-alanine amidase.

Effects of oxygen on biofilm formation and the AtlA autolysin of Streptococcus mutans.

The Streptococcus mutans atlA gene encodes an autolysin required for biofilm maturation and biogenesis of a normal cell surface. We found that the capacity to form biofilms by S. mutans, one of the principal causative agents of dental caries, was dramatically impaired by growth of the organism in an aerated environment and that cells exposed to oxygen displayed marked changes in surface protein profiles. Inactivation of the atlA gene alleviated repression of biofilm formation in the presence of oxygen. Also, the formation of long chains, a characteristic of AtlA-deficient strains, was less evident in cells grown with aeration. The SMu0629 gene is immediately upstream of atlA and encodes a product that contains a C-X-X-C motif, a characteristic of thiol-disulfide oxidoreductases. Inactivation of SMu0629 significantly reduced the levels of AtlA protein and led to resistance to autolysis. The SMu0629 mutant also displayed an enhanced capacity to form biofilms in the presence of oxygen compared to that of the parental strain. The expression of SMu0629 was shown to be under the control of the VicRK two-component system, which influences oxidative stress tolerance in S. mutans. Disruption of vicK also led to inhibition of processing of AtlA, and the mutant was hyperresistant to autolysis. When grown under aerobic conditions, the vicK mutant also showed significantly increased biofilm formation compared to strain UA159. This study illustrates the central role of AtlA and VicK in orchestrating growth on surfaces and envelope biogenesis in response to redox conditions.