Identification and characterization of the S-layer formed on the sheath of Thiothrix nivea

Production of a cellulose-aminating polysaccharide from a filamentous sulfur-oxidizing bacterium, Thiothrix nivea, grown lithotrophically or mixotrophically

AIMS

Glucosaminoglucan (β-1,4-linked glucose and glucosamine) produced by a mixotrophic sulfur-oxidizing bacterium, Thiothrix nivea, is a useful cellulose-aminating agent. Lithotrophic and mixotrophic glucosaminoglucan production were examined using fed-batch techniques.

METHODS AND RESULTS

A jar fermenter was used for the fed-batch cultivation. Glucosaminoglucan was extracted from T. nivea using diluted HCl. Lithotrophic growth was detected by feeding with Na2S as the energy source, and 12 mg l-1 of glucosaminoglucan was obtained. In contrast, no growth was observed with Na2S2O3. Similarly, mixotrophic growth in the presence of acetic acid was promoted by Na2S, whereas Na2S2O3 had no effect. When acetic acid and Na2S were added, 470 mg l-1 of glucosaminoglucan was obtained.

CONCLUSIONS

Thiothrix nivea was cultured, and glucosaminoglucan was produced lithotrophically using Na2S for feeding. Na2S is also indispensable for mixotrophic growth and glucosaminoglucan production, indicating that sulfide oxidation pathways control the TCA cycle. The involvement of the SOX pathway (for thiosulfate oxidation) in the activation of energy metabolism is doubtful because neither lithotrophic nor mixotrophic growth was promoted by Na2S2O3. Based on these results, we assumed that T. nivea is facultatively mixotrophic [lithotrophic growth is possible in addition to organotrophic growth in the presence of sulfide (Na2S)], rather than obligately mixotrophic.

Negative role of filamentous bulking and its elimination in anammox process

In this study, the filamentous bulking (FB) with moderate and excessive levels were demonstrated to induce anammox failure by inhibiting nitrogen (N) removal and biomass retention. The low external mass transfer resulted from high liquid-surface friction and low turbulence of filamentous surface was considered the "trigger" of anammox failure, which decreased flux of nitrogen flow toward granular surface and directly limited N-removal loading, which meanwhile exposed granules with N-scarcity environment and indirectly inhibited N-removal bio-activity. Low bio-activity performed poor extracellular polymeric substances secretion further destroyed bio-aggregation with low suface hydrophobicity, which acted as "accelerator" for granule disintegration and biomass washout, ultimatly leading to anammox failure. Fortunately, incresing hydraulic shear stress could eradicate FB's negative effects without inhibiting FB itself, which promoted re-granulation and N-remval restore by enhancing external mass transfer more than hydraulic detachment. Enhancing mechanical stirring with FB level was necessary to maintain stable operation of granular anammox system.

Leptothrix cholodnii Response to Nutrient Limitation

Microorganisms are widely utilized for the treatment of wastewater in activated sludge systems. However, the uncontrolled growth of filamentous bacteria leads to bulking and adversely affects wastewater treatment efficiency. To clarify the nutrient requirements for filament formation, we track the growth of a filamentous bacterium, Leptothrix cholodnii SP-6 in different nutrient-limited conditions using a high aspect-ratio microfluidic chamber to follow cell-chain elongation and sheath formation. We find that limitations in Na⁺, K⁺, and Fe²⁺ yield no observable changes in the elongation of cell chains and sheath formation, whereas limitations of C, N, P, or vitamins lead to more pronounced changes in filament morphology; here we observe the appearance of partially empty filaments with wide intercellular gaps. We observe more dramatic differences when SP-6 cells are transferred to media lacking Mg²⁺ and Ca²⁺. Loss of Mg²⁺ results in cell autolysis, while removal of Ca²⁺ results in the catastrophic disintegration of the filaments. By simultaneously limiting both carbon and Ca²⁺ sources, we are able to stimulate planktonic cell generation. These findings paint a detailed picture of the ecophysiology of Leptothrix, which may lead to improved control over the unchecked growth of deleterious filamentous bacteria in water purification systems.

Environmental Conditions Modulate the Transcriptomic Response of Both Caulobacter crescentus Morphotypes to Cu Stress

Bacteria encounter elevated copper (Cu) concentrations in multiple environments, varying from mining wastes to antimicrobial applications of copper. As the role of the environment in the bacterial response to Cu ion exposure remains elusive, we used a tagRNA-seq approach to elucidate the disparate responses of two morphotypes of Caulobacter crescentus NA1000 to moderate Cu stress in a complex rich (PYE) medium and a defined poor (M2G) medium. The transcriptome was more responsive in M2G, where we observed an extensive oxidative stress response and reconfiguration of the proteome, as well as the induction of metal resistance clusters. In PYE, little evidence was found for an oxidative stress response, but several transport systems were differentially expressed, and an increased need for histidine was apparent. These results show that the Cu stress response is strongly dependent on the cellular environment. In addition, induction of the extracytoplasmic function sigma factor SigF and its regulon was shared by the Cu stress responses in both media, and its central role was confirmed by the phenotypic screening of a sigF::Tn5 mutant. In both media, stalked cells were more responsive to Cu stress than swarmer cells, and a stronger basal expression of several cell protection systems was noted, indicating that the swarmer cell is inherently more Cu resistant. Our approach also allowed for detecting several new transcription start sites, putatively indicating small regulatory RNAs, and additional levels of Cu-responsive regulation.

Aggregability of β(1→4)-linked glucosaminoglucan originating from a sulfur-oxidizing bacterium Thiothrix nivea

β-1,4-glucosaminoglucan (GG) was prepared from the sheath of a sulfur-oxidizing bacterium Thiothrix nivea. Recently, GG was found to be adsorbed by cellulose (paper) and is therefore potentially applicable as an aminating agent for cellulose. We attempted to increase the yield of GG using a fed-batch cultivation method. Furthermore, the behavior of GG molecules in water was theoretically and experimentally investigated. NMR analysis in combination with molecular dynamics calculation suggested that GG molecules tend to form soluble aggregates in water. It was experimentally revealed that the self-aggregation is enhanced by the addition of NaCl and reduced temperature. Adsorption of GG onto cellulose via hydrogen bonding was confirmed by molecular dynamics simulation. Adsorption was also promoted in the presence of NaCl but was inhibited by a reduction in temperature. Only 11% of the amino groups in the GG-treated paper was reactive, suggesting that GG molecules adsorbed by the paper were forming aggregates.

Polyfunctional Nanofibril Appendages Mediate Attachment, Filamentation, and Filament Adaptability in Leptothrix cholodnii

Leptothrix is a species of Fe/Mn-oxidizing bacteria known to form long filaments composed of chains of cells that eventually produce a rigid tube surrounding the filament. Prior to the formation of this brittle microtube, Leptothrix cells secrete hair-like structures from the cell surface, called nanofibrils, which develop into a soft sheath that surrounds the filament. To clarify the role of nanofibrils in filament formation in L. cholodnii SP-6, we analyze the behavior of individual cells and multicellular filaments in high-aspect ratio microfluidic chambers using time-lapse and intermittent in situ fluorescent staining of nanofibrils, complemented with atmospheric scanning electron microscopy. We show that in SP-6 nanofibrils are important for attachment and their distribution on young filaments post-attachment is correlated to the directionality of filament elongation. Elongating filaments demonstrate a surprising ability to adapt to their physical environment by changing direction when they encounter obstacles: they bend or reverse direction depending on the angle of the collision. We show that the forces involved in the collision can be used to predict the behavior of filament. Finally, we show that as filaments grow in length, the older region becomes confined by the sheath, while the newly secreted nanofibrils at the leading edge of the filament form a loose, divergent, structure from which cells periodically escape.