Photosystem II (PSII) uses solar energy to oxidize water and delivers electrons for life on Earth. The photochemical reaction center of PSII is known to possess two stationary states. In the open ...state (PSIIO), the absorption of a single photon triggers electron-transfer steps, which convert PSII into the charge-separated closed state (PSIIC). Here, by using steady-state and time-resolved spectroscopic techniques on Spinacia oleracea and Thermosynechococcus vulcanus preparations, we show that additional illumination gradually transforms PSIIC into a light-adapted charge-separated state (PSIIL). The PSIIC-to-PSIIL transition, observed at all temperatures between 80 and 308 K, is responsible for a large part of the variable chlorophyll-a fluorescence (Fv) and is associated with subtle, dark-reversible reorganizations in the core complexes, protein conformational changes at noncryogenic temperatures, and marked variations in the rates of photochemical and photophysical reactions. The build-up of PSIIL requires a series of light-induced events generating rapidly recombining primary radical pairs, spaced by sufficient waiting times between these events-pointing to the roles of local electric-field transients and dielectric relaxation processes. We show that the maximum fluorescence level, Fm, is associated with PSIIL rather than with PSIIC, and thus the Fv/Fm parameter cannot be equated with the quantum efficiency of PSII photochemistry. Our findings resolve the controversies and explain the peculiar features of chlorophyll-a fluorescence kinetics, a tool to monitor the functional activity and the structural-functional plasticity of PSII in different wild-types and mutant organisms and under stress conditions.
The purpose of this review is to outline our understanding of the nature, mechanism and physiological significance of light-induced reversible reorganizations in closed Type II reaction centre (RC) ...complexes. In the so-called 'closed' state, purple bacterial RC (bRC) and photosystem II (PSII) RC complexes are incapable of generating additional stable charge separation. Yet, upon continued excitation they display well-discernible changes in their photophysical and photochemical parameters. Substantial stabilization of their charge-separated states has been thoroughly documented-uncovering light-induced reorganizations in closed RCs and revealing their physiological importance in gradually optimizing the operation of the photosynthetic machinery during the dark-to-light transition. A range of subtle light-induced conformational changes has indeed been detected experimentally in different laboratories using different bRC and PSII-containing preparations. In general, the presently available data strongly suggest similar structural dynamics of closed bRC and PSII RC complexes, and similar physical mechanisms, in which dielectric relaxation processes and structural memory effects of proteins are proposed to play important roles.
In our earlier works, we have identified rate-limiting steps in the dark-to-light transition of PSII. By measuring chlorophyll a fluorescence transients elicited by single-turnover saturating flashes ...(STSFs) we have shown that in diuron-treated samples an STSF generates only F1 (< Fm) fluorescence level, and to produce the maximum (Fm) level, additional excitations are required, which, however, can only be effective if sufficiently long Δτ waiting times are allowed between the excitations. Biological variations in the half-rise time (Δτ1/2) of the fluorescence increment suggest that it may be sensitive to the physicochemical environment of PSII. Here, we investigated the influence of the lipidic environment on Δτ1/2 of PSII core complexes of Thermosynechococcus vulcanus. We found that while non-native lipids had no noticeable effects, thylakoid membrane lipids considerably shortened the Δτ1/2, from ~ 1 ms to ~ 0.2 ms. The importance of the presence of native lipids was confirmed by obtaining similarly short Δτ1/2 values in the whole T. vulcanus cells and isolated pea thylakoid membranes. Minor, lipid-dependent reorganizations were also observed by steady-state and time-resolved spectroscopic measurements. These data show that the processes beyond the dark-to-light transition of PSII depend significantly on the lipid matrix of the reaction center.
The kinetics of bacteriochlorophyll fluorescence in intact cells of the purple nonsulfur bacterium
Rhodobacter sphaeroides
were measured under continuous and pulsed actinic laser diode (808 nm ...wavelength and maximum 2 W light power) illumination on the micro- and millisecond timescale. The fluorescence induction curve was interpreted in terms of a combination of photochemical and triplet fluorescence quenchers and was demonstrated to be a reflection of redox changes and electron carrier dynamics. By adjustment of the conditions of single and multiple turnovers of the reaction center, we obtained 11 ms
–1
and 120 μs
–1
for the rate constants of cytochrome
c
2
3+
detachment and cyclic electron flow, respectively. The effects of cytochrome
c
2
deletion and chemical treatments of the bacteria and the advantages of the fluorescence induction study on the operation of the electron transport chain
in vivo
were discussed.
The development of photosynthetic membranes of intact cells of Rhodobacter sphaeroides was tracked by light-induced absorption spectroscopy and induction and relaxation of the bacteriochlorophyll ...fluorescence. Changes in membrane structure were induced by three methods: synchronization of cell growth, adjustment of different growth phases and transfer from aerobic to anaerobic conditions (greening) of the bacteria. While the production of the bacteriochlorophyll and carotenoid pigments and the activation of light harvesting and reaction center complexes showed cell-cycle independent and continuous increase with characteristic lag phases, the accumulation of phospholipids and membrane potential (electrochromism) exhibited stepwise increase controlled by cell division. Cells in the stationary phase of growth demonstrated closer packing and tighter energetic coupling of the photosynthetic units (PSU) than in their early logarithmic stage. The greening resulted in rapid (within 0–4 h) induction of BChl synthesis accompanied with a dominating role for the peripheral light harvesting system (up to LH2/LH1 ~2.5), significantly increased rate (~7·10⁴ s⁻¹) and yield (F ᵥ/F ₘₐₓ ~0.7) of photochemistry and modest (~2.5-fold) decrease of the rate of electron transfer (~1.5·10⁴ s⁻¹). The results are discussed in frame of a model of sequential assembly of the PSU with emphasis on crowding the LH2 complexes resulting in an increase of the connectivity and yield of light capture on the one hand and increase of hindrance to diffusion of mobile redox agents on the other hand.
Many different bacterial species have the ability to cause an infection of the bovine mammary gland and the host response to these infections is what we recognize as mastitis. In this review we ...evaluate the pathogen specific response to the three main bacterial species causing bovine mastitis:
Escherichia coli,
Streptococcus uberis and
Staphylococcus aureus. In this paper we will review the bacterial growth patterns, host immune response and clinical response that results from the intramammary infections. Clear differences in bacterial growth pattern are shown between bacterial species. The dominant pattern in
E. coli infections is a short duration high bacteria count infection, in
S. aureus this is more commonly a persistent infection with relative low bacteria counts and in
S. uberis a long duration high bacteria count infection is often observed. The host immune response differs significantly depending on the invading bacterial species. The underlying reasons for the differences and the resulting host response are described. Finally we discuss the clinical response pattern for each of the three bacterial species. The largest contrast is between
E. coli and S. aureus where a larger proportion of
E. coli infections cause potentially severe clinical symptoms, whereas the majority of
S. aureus infections go clinically unnoticed.
The relevance of fully understanding the bovine host response to intramammary infection is discussed, some major gaps in our knowledge are highlighted and directions for future research are indicated.
Determining the species of mycoplasma isolated from culture-positive milk samples is important for understanding the clinical significance of their detection. Between August 2016 and December 2019, ...214,518 milk samples from 2,757 dairy herds were submitted to Quality Milk Production Services (QMPS) at Cornell University for mycoplasma culture. From these samples, 3,728 collected from 204 herds were culture positive. Based on the request of herd managers, owners, or veterinarians, 889 isolates from 98 herds were subjected to molecular identification by PCR and amplicon sequencing. The largest proportion of the identified isolates were from New York State (78.1%), while the others came from the eastern United States (17.8%), Texas (2.0%), and New Mexico (2.1%). As expected, Mycoplasma spp. were the most common (855 isolates, 96.2%) and Acholeplasma spp. accounted for the remainder (34 isolates, 3.8%). Mycoplasma bovis was the most prevalent Mycoplasma species (75.1%), followed by M. bovigenitalium (6.5%), M. canadense (5.9%), M. alkalescens (5%), M. arginini (1.7%), M. californicum (0.1%), and M. primatum (0.1%). A portion of the isolates were confirmed as Mycoplasma spp. other than M. bovis but were not identified at the species level (16 isolates, 1.8%) because further information was not requested by the manager, owner, or veterinarian. Mycoplasma bovis was the only species identified in 59 of the 98 herds. However, more than 1 Mycoplasma sp. was identified in 29 herds, suggesting that herd infection with 2 or more mycoplasmas is not uncommon. Moreover, a Mycoplasma sp. other than M. bovis was the only species identified in 8 herds. From the subset of 889 mycoplasma culture-positive isolates from 98 herds, we determined that over a third of the herds had either more than 1 Mycoplasma sp. or a Mycoplasma sp. other than M. bovis detected in their milk samples. In conclusion, we observed that M. bovis is the most common pathogenic Mycoplasma species found in mastitic milk, but other Mycoplasma species are not uncommon. Our results suggest that it is critical to test milk samples for mycoplasmas using diagnostic tests able to identify both the genus and the species.
In-depth analysis of colostrum components has identified hundreds of proteins, but data are sparse regarding their systemic uptake in the newborn calf. Moreover, heat treatment may influence these ...colostral components and their absorption. Our objectives were to describe the serum proteome of newborn calves before and after colostrum feeding and the possible effects of colostral heat treatment. Newborn Holstein heifer calves (n = 22) were randomized within pair and fed heat-treated (n = 11; 60°C, 60 min) or raw (n = 11) colostrum at 8.5% of birth body weight by esophageal feeder within 1 h of birth. After the single colostrum feeding, calves were not fed until after the 8-h time point, when milk was offered free-choice. Blood samples were taken immediately before feeding (0 h), as well as 4, 8, and 24 h after feeding. Whole blood packed cell volume (%), serum Brix percentage, and plasma glucose concentrations were determined for all time points. Plasma insulin and insulin-like growth factor-I concentrations were determined by radioimmunoassay for selected time points. Serum IgA and IgG were measured by radial immunodiffusion at 24 h. The serum proteome was analyzed using nano-scale reverse-phase chromatography and tandem mass spectrometry (nano LC-MS/MS) in 0- and 8-h samples. For proteomics analysis, ratios of results for 8-h to 0-h samples were analyzed with false discovery rate adjustment. For all other outcomes, repeated-measures ANOVA was performed with the fixed effects of group, time, and their interaction, and random effect of pair. Serum Brix percentage and glucose concentrations increased over time and were independent of colostrum treatment. Serum IgG and IgA concentrations at 24 h did not differ between groups. Nano LC-MS/MS identified a total of 663 unique proteins in serum, of which 261 increased in abundance, whereas 67 decreased in abundance after feeding in both groups. Among serum proteins that increased in abundance and that were previously identified in colostrum, many belonged to those involved in immune response, coagulation, the classical complement pathway, or the antimicrobial peptide class of cathelicidins. Serum proteins that decreased in abundance and that were identified in colostrum belonged to the alternative complement pathway and the membrane attack complex. Thirty-eight proteins differed in calves that were fed heat-treated colostrum compared with those fed raw colostrum. Decreased abundances in calves fed heat-treated colostrum included several enzymes involved in glycolysis or glycogenolysis, whereas the incretin gastric inhibitory polypeptide and serum insulin were increased in this group. Our findings point to important innate immune defense pathways associated with colostrum ingestion in newborn calves. Furthermore, calves fed heat-treated colostrum showed differences in serum proteins and enzymes associated with carbohydrate metabolism.
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