Membrane fluidity adaptation to the low growth temperature in Bacillus subtilis involves two distinct mechanisms: (1) long-term adaptation accomplished by increasing the ratio of anteiso- to iso-branched fatty acids and (2) rapid desaturation of fatty acid chains in existing phospholipids by induction of fatty acid desaturase after cold shock. In this work we studied the effect of medium composition on cold adaptation of membrane fluidity. Bacillus subtilis was cultivated at optimum (40 degrees C) and low (20 degrees C) temperatures in complex medium with glucose or in mineral medium with either glucose or glycerol. Cold adaptation was characterized by fatty acid analysis and by measuring the midpoint of phospholipid phase transition T(m) (differential scanning calorimetry) and membrane fluidity (DPH fluorescence polarization). Cells cultured and measured at 40 degrees C displayed the same membrane fluidity in all three media despite a markedly different fatty acid composition. The T(m) was surprisingly the highest in the case of a culture grown in complex medium. On the contrary, cultivation at 20 degrees C in the complex medium gave rise to the highest membrane fluidity with concomitant decrease of T(m) by 10.5 degrees C. In mineral media at 20 degrees C the corresponding changes of T(m) were almost negligible. After a temperature shift from 40 to 20 degrees C, the cultures from all three media displayed the same adaptive induction of fatty acid desaturase despite their different membrane fluidity values immediately after cold shock.

In this study, we investigated the potential antibacterial properties of nanocrystalline diamond. In particular, we tested the effect of diamond nanoparticles (DNPs) on growth of the model gram-negative bacterium Escherichia coli on solid, nutrient-rich growth medium. We found that the presence of DNPs on agar plates significantly reduced the colony forming ability of E. coli. The antibacterial effect occurred in a concentration dependent manner and was conditional on the specific ratio of DNPs to the number of bacterial cells.

In this study, the influence of the size and surface termination of diamond nanoparticles (DNPs) on their antibacterial activity against Escherichia coli and Bacillus subtilis was assessed. The average size and distribution of DNPs were determined by dynamic light scattering and X-ray diffraction techniques. The chemical composition of the DNPs studied by X-ray photoelectron spectroscopy showed that DNPs > 5 nm and oxidized particles have a higher oxygen content. The antibacterial potential of DNPs was assessed by the viable count method. In general, E. coli exhibited a higher sensitivity to DNPs than B. subtilis. However, in the presence of all the DNPs tested, the B. subtilis colonies exhibited altered size and morphology. Antibacterial activity was influenced not only by DNP concentration but also by DNP size and form. Whereas untreated 5-nm DNPs were the most effective against E. coli, the antibacterial activity of 18-50-nm DNPs was higher against B. subtilis. Transmission electron microscopy showed that DNPs interact with the bacterial surface, probably affecting vital cell functions. We propose that DNPs interfere with the permeability of the bacterial cell wall and/or membrane and hinder B. subtilis colony spreading.

Bacillus subtilis, which grows under aerobic conditions, employs fatty acid desaturase (Des) to fluidize its membrane when subjected to temperature downshift. Des requires molecular oxygen for its activity, and its expression is regulated by DesK-DesR, a two-component system. Transcription of des is induced by the temperature downshift and is decreased when membrane fluidity is restored. B. subtilis is also capable of anaerobic growth by nitrate or nitrite respiration. We studied the mechanism of cold adaptation in B. subtilis under anaerobic conditions that were predicted to inhibit Des activity. We found that in anaerobiosis, in contrast to aerobic growth, the induction of des expression after temperature downshift (from 37°C to 25°C) was not downregulated. However, the transfer from anaerobic to aerobic conditions rapidly restored the downregulation. Under both aerobic and anaerobic conditions, the induction of des expression was substantially reduced by the addition of external fluidizing oleic acid and was fully dependent on the DesK-DesR twocomponent regulatory system. Fatty acid analysis proved that there was no desaturation after des induction under anaerobic conditions despite the presence of high levels of the des protein product, which was shown by immunoblot analysis. The cold adaptation of B. subtilis in anaerobiosis is therefore mediated exclusively by the increased anteiso/iso ratio of branched-chain fatty acids and not by the temporarily increased level of unsaturated fatty acids that is typical under aerobic conditions. The degrees of membrane fluidization, as measured by diphenylhexatriene fluorescence anisotropy, were found to be similar under both aerobic and anaerobic conditions.Bacterial growth requires an appreciable fraction of the acyl chains of the membrane lipids to be in a disordered state. Such disordered states are brought about by fatty acids that act to offset the closely packed ordered arrangement of the lipid bilayer acyl chains that are imparted by the straight-chain saturated acyl chains. In most bacteria, the role of introducing acyl chain disorder is fulfilled by unsaturated fatty acids. Some bacteria synthesize UFAs by the process of desaturation, an oxygen-requiring reaction that introduces the double bond into a single concerted reaction. However, this is not an option for bacteria that grow under anaerobic conditions. For example, in the upper layers of soil, which are the natural habitat of Bacillus subtilis, the fluctuations in oxygen availability that are mostly caused by the changing water content are common.Even though B. subtilis is still generally considered to be an obligate aerobe, several recent studies have proved that this bacterium is in fact a facultative anaerobe, which is capable of both fermentation and anaerobic respiration with either nitrate or nitrite used as the terminal electron acceptor (19,20). The key role in the complex regulation of anaerobic metabolism of B. subtilis can be attributed to the genes resD and resE (21, 26) and fnr (23).A decreas...

No abstract

Carbon nanomaterials such as nanodiamond (ND) and graphene oxide (GO) attract increasing attention for biomedical applications due their unique and adjustable properties. Here we report on antibacterial activity of NDs and GO as evaluated by bacterial colony counting. ND and GO were used in oxidized (O-ND, GO) or reduced (H-ND, rGO) forms. ND or GO are mixed in Mueller-Hinton (MH) broth with Escherichia coli at the concentration of 1 mg ml À1 . The resulting suspensions were cultivated for 5 and 24 h at 37 8C in a shaker. After each period, a sample of the suspension was spread on the MH agar and cultivated for 24 h at 378 C. The effect of nanomaterials on colony forming ability (CFA) of E. coli was evaluated and compared with the negative control sample. The most noticeable effect was that after 5 h H-ND decreased the CFA of E. coli in the MH broth by 60% and GO by 50%. After 24 h, H-ND decreased CFA by 50%. Other nanomaterials had no statistically significant antibacterial effect. Factors influencing ND and GO antibacterial activity against the E. coli and possibly against other bacteria are discussed.

No abstract

No abstract