Tuning and elucidation of the colony dimorphism in Rhodococcus ruber associated with cell flocculation in large scale fermentation

Enhancing the stress resistance of nitrile hydratase from Rhodococcus ruber via SpyTag/SpyCatcher-mediated α- and β- subunits ligation

BACKGROUND

Nitrile Hydratase (NHase) is one of the most important industrial enzyme widely used in the petroleum exploitation field. The enzyme, composed of two unrelated α- and β-subunits, catalyzes the conversion of acrylonitrile to acrylamide, releasing a significant amount of heat and generating the organic solvent product, acrylamide. Both the heat and acrylamide solvent have an impact on the structural stability of NHase and its catalytic activity. Therefore, enhancing the stress resistance of NHase to toxic substances is meaningful for the petroleum industry.

METHODS AND RESULTS

To improve the thermo-stability and acrylamide tolerance of NHase, the two subunits were fused in vivo using SpyTag and SpyCatcher, which were attached to the termini of each subunit in various combinations. Analysis of the engineered strains showed that the C-terminus of β-NHase is a better fusion site than the N-terminus, while the C-terminus of α-NHase is the most suitable site for fusion with a larger protein. Fusion of SpyTag and SpyCatcher to the C-terminus of β-NHase and α-NHase, respectively, led to improved acrylamide tolerance and a slight enhancement in the thermo-stability of one of the engineered strains, NBSt.

CONCLUSION

These results indicate that in vivo ligation of different subunits using SpyTag/SpyCatcher is a valuable strategy for enhancing subunit interaction and improving stress tolerance.

Rugose small colony variant and its hyper-biofilm in Pseudomonas aeruginosa: Adaption, evolution, and biotechnological potential

One of the hallmarks of the environmental bacterium Pseudomonas aeruginosa is its excellent ecological flexibility, which can thrive in diverse ecological niches. In different ecosystems, P. aeruginosa may use different strategies to survive, such as forming biofilms in crude oil environment, converting to mucoid phenotype in the cystic fibrosis (CF) lung, or becoming persisters when treated with antibiotics. Rugose small colony variants (RSCVs) are the adaptive mutants of P. aeruginosa, which can be frequently isolated from chronic infections. During the past years, there has been a renewed interest in using P. aeruginosa as a model organism to investigate the RSCVs formation, persistence and pathogenesis, as RSCVs represent a hyper-biofilm formation, high adaptability, high-tolerance sub-population in biofilms. This review will briefly summarize recent advances regarding the phenotypic, genetic and host interaction associated with RSCVs, with an emphasis on P. aeruginosa. Meanwhile, some non-pathogenic bacteria such as Pseudomonas fluorescence, Pseudomonas putida and Bacillus subtilis will be also included. Remarkable emphasis is given on intrinsic functions of such hyper-biofilm formation characteristic as well as its potential applications in several biocatalytic transformations including wastewater treatment, microbial fermentation, and plastic degradation. Hopefully, this review will attract the interest of researchers in various fields and shape future research focused not only on evolutionary biology but also on biotechnological applications related to RSCVs.

Genomic analyses of two Alteromonas stellipolaris strains reveal traits with potential biotechnological applications

The Alteromonas stellipolaris strains PQQ-42 and PQQ-44, previously isolated from a fish hatchery, have been selected on the basis of their strong quorum quenching (QQ) activity, as well as their ability to reduce Vibrio-induced mortality on the coral Oculina patagonica. In this study, the genome sequences of both strains were determined and analyzed in order to identify the mechanism responsible for QQ activity. Both PQQ-42 and PQQ-44 were found to degrade a wide range of N-acylhomoserine lactone (AHL) QS signals, possibly due to the presence of an aac gene which encodes an AHL amidohydrolase. In addition, the different colony morphologies exhibited by the strains could be related to the differences observed in genes encoding cell wall biosynthesis and exopolysaccharide (EPS) production. The PQQ-42 strain produces more EPS (0.36 g l-1) than the PQQ-44 strain (0.15 g l-1), whose chemical compositions also differ. Remarkably, PQQ-44 EPS contains large amounts of fucose, a sugar used in high-value biotechnological applications. Furthermore, the genome of strain PQQ-42 contained a large non-ribosomal peptide synthase (NRPS) cluster with a previously unknown genetic structure. The synthesis of enzymes and other bioactive compounds were also identified, indicating that PQQ-42 and PQQ-44 could have biotechnological applications.

Improving stress tolerance and cell integrity of Rhodococcus ruber by overexpressing small-shock-protein Hsp16 of Rhodococcus

Rhodococcus species have been successfully used as cell catalysts for valuable chemicals production due to their well-characterized resistance to harmful factors. An understanding of how they respond to stress is of great interest, which will enable the identification of engineering strategies for further improving their resistance and maintaining cell integrity and viability. Here, we assessed the transcriptome response of R. ruber TH3 to heat shock. Approximately, 376 genes were up-regulated in heat-shocked TH3. Among all the up-regulated functional genes, the small heat-shock-protein (Hsp16) with maximal enhanced transcript (463-fold) was identified, and its function was investigated. Results showed that overexpressed Hsp16 has no significant promotive effect on stress tolerance of in-cell enzyme. Interestingly, compared to the control TH3, a little fewer pores and folds on the surface of TH3(Hsp16) and more intact TH3(Hsp-GFP) cells under AM treatment were observed by SEM and LCSM, respectively. Moreover, survival test showed that more (about 501–700) TH3(Hsp16) colonies were observed while only 1–100 TH3 colonies after 50% AM treatment, and this trend is also found in high-temperature cultivation experiments. These results indicate that Hsp16 does great contributions to preventing cell leakage, maintaining cell integrity and viability of R. ruber under stress conditions.