Non-optimal pH Research Articles

Initial pH determines the morphological characteristics and secondary metabolite production in Aspergillus terreus and Streptomyces rimosus cocultures

The influence of the initial pH on the morphology and secondary metabolite production in cocultures and axenic cultures of Aspergillus terreus and Streptomyces rimosus was investigated. The detected secondary metabolites (6 of bacterial and 4 of fungal origin) were not found in the cultures initiated at pH values less than or equal to 4.0. The highest mean levels of oxytetracycline were recorded in S. rimosus axenic culture at pH 5.0. Initiating the axenic culture at pH 5.9 led to visibly lower product levels, yet the presence of A. terreus reduced the negative effect of non-optimal pH and led to higher oxytetracycline titer than in the corresponding S. rimosus axenic culture. The cocultivation initiated at pH 5.0 or 5.9 triggered the formation of oxidized rimocidin. The products of A. terreus were absent in the cocultures. At pH 4.0, the striking morphological differences between the coculture and the axenic cultures were recorded.

Advanced electrochemical strategies for simultaneous removal of Microcystis aeruginosa and microcystin-LR: On-demand optimization and mechanistic insights

The frequent occurrence of harmful cyanobacterial blooms and toxins poses significant threats to aquatic life and drinking water safety. This work reports the removal mechanisms of M. aeruginosa and microcystin-LR (MC-LR) using the Pt-Graphite felt (GF) electrochemical system, which builds upon prior research to investigate diverse processes driven by distinct mechanisms within a single reactor, primarily by pH regulation. Factors affecting removal were assessed through single-factor trials and Box-Behnken design, identifying optimal conditions for successful algae removal, finally a 96% removal efficiency of algae cells and an 83% elimination efficiency of MC-LR within a 60-minute timeframe. Particularly at non-optimal pH 7 conditions, the Pt-GF system showcases synergistic effects, enhancing electro-flocculation and weakening electro-Fenton reactions. Conversely, at an optimal pH of 3, the electro-Fenton process is favorably enhanced, leading to improved removal efficiency through escalated reactive oxygen species generation. Additionally, the system exhibits consistent repeatability in its performance. Notably, its effectiveness is substantiated across varying nitrogen and phosphorus levels and in simulated water samples containing multiple algal species. In essence, this subtly adaptable reactor tuning integrates electro-Fenton, electro-flocculation, electro-adsorption, and electrochemical direct oxidation effects for the first time, potentially providing a more effective and manageable solution for addressing harmful algae in water.

Opting for polyamines with specific structural traits as a strategy to boost performance of enzymatic membrane reactors

Enzymatic membrane reactor (EMR) is a type of continuous-flow bioreactor offering easy separation and reuse of biocatalyst while giving opportunities to improve its performance. However, simultaneous enhancement of activity and stability of enzyme while retaining high membrane permeability poses a challenge for a single reactor. Herein, we propose a new method to optimize EMR system − by employing cationic polyelectrolytes with selected molecular weight, backbone, and amino group type for modification of membrane surface; after we have evaluated the effect of polyamine chemistry and membrane properties on each aspect of EMR performance. Polydopamine (PDA)-assisted co-deposition of polyamines (polyethyleneimine (PEI), PEI-graft-poly(ethylene glycol) (PEI-g-PEG), poly(allylamine hydrochloride) (PAH), and poly(diallyldimethylammonium chloride) (PDADMAC)) was used as the modification method; the membranes were characterized by water permeability, water contact angle (WCA), zeta potential (ZP), FTIR spectra, and SEM/EDX; and EMRs were assessed by biocatalytic activity at various pH, flux, immobilization yield and efficiency (activity recovery), enzyme leakage, pH/storage and thermal stability, and reusability. In this work, EMRs with immobilized alcohol dehydrogenase (ADH) showed activities up to 8.9 mU/cm2, retained up to 86 % of initial activity in three conversion cycles without any reduction in flux, and allowed to increase non-optimal pH activity (pH 10) by up to 81 % and improve storage stability by up to 53 % compared to the free enzyme. We discovered statistically significant (p < 0.01) relationships between: (1) polyamine backbone type (linear vs branched) and membrane permeability; (2) membrane isoelectric point and immobilization yield; and (3) membrane WCA and immobilization efficiency. To our knowledge, this is the first systematic study of the effect of polyelectrolyte chemistry on performance of immobilized enzyme − which showed the method’s strong potential for customizing properties and maximizing the productivity of EMRs.

Influence of Satiation Feeding on the Water Quality and the Growth, Hematological Parameters, and Blood Chemistry of Nile Tilapia Oreochromis niloticus Reared in Nutrient Film Technique Aquaponic System

One of the most significant inputs in an aquaponic system is fish feed. Here, two satiation feeding (SF) levels (60% & 50%) have been tested. It aims to determine its effect on the water quality and the growth, hematological indices, and blood chemistry of Nile tilapia Oreochromis niloticus reared in nutrient film technique aquaponic system (NFTAS) containing upland kangkong Ipomea reptans within 1 month period and compared it in the recirculating system (RS). Results showed that the SF levels have an insignificant effect on the water quality between the systems mainly due to the nonoptimal pH level that influenced the nitrification efficiency and the inefficient uptake of nutrients by the plants in NFTAS. Consequently, the growth, hematological parameters, and blood chemistry of the fish reared in NFTAS have not improved compared with those in RS. However, the fish and the plant growth performance were better at 60% SF in both systems. Thus, 60% is suggested SF level when 200 individuals Nile tilapia O. niloticus tilapia fingerling (2.46 g, average initial weight) are reared within 31 days in a healthy and balanced NFTAS with 50 individuals upland kangkong I. reptans.

Ultrasound processing of amyloglucosidase: impact on enzyme activity, stability and possible industrial applications

This study evaluated the effect of ultrasound processing as a pre-treatment of amyloglucosidase on the enzymatic activity and stability. The activity was evaluated under optimal (65°C/ pH = 4.5) and non-optimal conditions of temperature and pH and its stability was evaluated during storage at 8°C. The enzyme solution was processed at 9.5 W L-1, 40 kHz, 23°C and at pH 3.5, 4.5, and 5.5, for up to 120 min. The activity was measured at 35, 65 and 80°C. The US process was able to increase, reduce or not alter the enzymatic activity, depending on the conditions applied. These modifications depended on the pH of the enzyme solution, the ultrasound processing time and the activity temperature. In different ultrasound conditions, mainly at 35 and 65°C, the enzyme activity did not change, demonstrating that this technology can be used for other purposes, such as microbial inactivation, without affecting the enzyme. The activity increase (up to 15%) occurred under non-optimal pH and temperature conditions (pH 3.5 or 5.5/ 80°C), suggesting that ultrasound promoted stabilization and enzymatic protection. This result is interesting in the starch saccharification, which requires the enzymatic reaction at high temperatures. Therefore, such results can increase the application range of this enzyme in different industrial applications.

Amine, thiol, and octyl functionalization of GO-Fe3O4 nanocomposites to enhance immobilization of lipase for transesterification

A novel immobilization support for Candida rugosa lipase Type VII (CRL7) is presented in the form of an octyl-functionalized magnetic graphene oxide nanocomposite (GO-Fe3O4). Immobilized lipase on this support is demonstrated to have 94.7% activity relative to free enzyme (34.5 U/mg-lipase), a transesterification yield of 89%, and a retained activity of 63% after 10 cycles. The octyl-functionalized GO-Fe3O4 nanocomposite (GO-Fe3O4@OTMS) is shown to perform better than graphene oxide (GO) and functionalized nanocomposites with amine and thiol groups. X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller method, and vibrating sample magnetometry were used to characterize the functionalized nanocomposites, demonstrating that Fe3O4 nanoparticles with an average crystallite size of 13.9 nm were deposited on GO layers. The Bradford assays showed that the amount of immobilized CRL7 was significantly increased from 187.4 mg lipase/g-nanocomposite for unfunctionalized GO-Fe3O4 to 328.6, 265.3, and 413.2 mg lipase/g-nanocomposite after functionalization of the nanocomposites (GO-Fe3O4) using (3-aminopropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, and (3-octyl)trimethoxysilane, respectively. The hydrolytic specific activity and transesterification of the immobilized lipase on GO-Fe3O4 were greatly enhanced by the functionalization of the nanocomposite. The optimal pH for the relative activity of CRL7 was shifted from 7 for free CRL7 and immobilized CRL7 on GO and GO-Fe3O4 to 8 for the functionalized nanocomposite. Furthermore, functionalization was also shown to maintain higher relative activity at non-optimal pH and to improve thermal stability.

Analyzing pepsin degradation assay conditions used for allergenicity assessments to ensure that pepsin susceptible and pepsin resistant dietary proteins are distinguishable.

The susceptibility of a dietary protein to proteolytic degradation by digestive enzymes, such as gastric pepsin, provides information on the likelihood of systemic exposure to a structurally intact and biologically active macromolecule, thus informing on the safety of proteins for human and animal consumption. Therefore, the purpose of standardized in vitro degradation studies that are performed during protein safety assessments is to distinguish whether proteins of interest are susceptible or resistant to pepsin degradation via a study design that enables study-to-study comparison. Attempting to assess pepsin degradation under a wide-range of possible physiological conditions poses a problem because of the lack of robust and consistent data collected under a large-range of sub-optimal conditions, which undermines the needs to harmonize in vitro degradation conditions. This report systematically compares the effects of pH, incubation time, and pepsin-to-substrate protein ratio on the relative degradation of five dietary proteins: three pepsin susceptible proteins [ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco), horseradish peroxidase (HRP), hemoglobin (Hb)], and two pepsin resistant proteins [lipid transfer protein (LTP) and soybean trypsin inhibitor (STI)]. The results indicate that proteins susceptible to pepsin degradation are readily distinguishable from pepsin-resistant proteins when the reaction conditions are within the well-characterized optima for pepsin. The current standardized in vitro pepsin resistant assay with low pH and high pepsin-to-substrate ratio fits this purpose. Using non-optimal pH and/or pepsin-to-substrate protein ratios resulted in susceptible proteins no longer being reliably degraded by this stomach enzyme, which compromises the ability of this in vitro assay to distinguish between resistant and susceptible proteins and, therefore, no longer providing useful data to an overall weight-of-evidence approach to assessing safety of proteins.

Effect of pH on soil bacterial diversity

In order to evaluate the effect of pH, known as a critical factor for shaping the biogeographical microbial patterns in the studies by others, on the bacterial diversity, we selected two sites in a similar geographical location (site 1; north latitude 35.3, longitude 127.8, site 2; north latitude 35.2, longitude 129.2) and compared their soil bacterial diversity between them. The mountain soil at site 1 (Jiri National Park) represented naturally acidic but almost pollution free (pH 5.2) and that at site 2 was neutral but exposed to the pollutants due to the suburban location of a big city (pH 7.7). Metagenomic DNAs from soil bacteria were extracted and amplified by PCR with 27F/518R primers and pyrosequenced using Roche 454 GS FLX Titanium. Bacterial phyla retrieved from the soil at site 1 were more diverse than those at site 2, and their bacterial compositions were quite different: Almost half of the phyla at site 1 were Proteobacteria (49 %), and the remaining phyla were attributed to 10 other phyla. By contrast, in the soil at site 2, four main phyla (Actinobacteria, Bacteroidetes, Proteobacteria, and Cyanobacteria) composed 94 %; the remainder was attributed to two other phyla. Furthermore, when bacterial composition was examined on the order level, only two Burkholderiales and Rhizobiales were found at both sites. So depending on pH, the bacterial community in soil at site 1 differed from that at site 2, and although the acidic soil of site 1 represented a non-optimal pH for bacterial growth, the bacterial diversity, evenness, and richness at this site were higher than those found in the neutral pH soil at site 2. These results and the indices regarding diversity, richness, and evenness examined in this study indicate that pH alone might not play a main role for bacterial diversity in soil.

About the cause of the stimulative effect of humate in yeast cultures

Trials were undertaken to elucidate the stimulating effect of sodium humate on yeast multiplication and the intensity of their fermentation. This effect appears specifically at pH non-optimal for the medium. No correlation was found between this effect and the complex-forming properties of various natural and synthetic humate fractions or the concentration of phosphate and calcium ions in the medium. Application of cystein as reducing agent, aeration of the medium and addition of detergents to it did not substitute the effect of humate. Tannin and gibberellin, on the other hand, stimulated cell proliferation and fermentation at non-optimal pH, remaining almost without influence at optimal pH, similarly as does humate.

Different response to acetic acid stress in Saccharomyces cerevisiae wild‐type and l‐ascorbic acid‐producing strains

Biotechnological processes are of increasing significance for industrial production of fine and bulk chemicals, including biofuels. Unfortunately, under operative conditions microorganisms meet multiple stresses, such as non-optimal pH, temperature, oxygenation and osmotic stress. Moreover, they have to face inhibitory compounds released during the pretreatment of lignocellulosic biomasses, which constitute the preferential substrate for second-generation processes. Inhibitors include furan derivatives, phenolic compounds and weak organic acids, among which acetic acid is one of the most abundant and detrimental for cells. They impair cellular metabolism and growth, reducing the productivity of the process: therefore, the development of robust cell factories with improved production rates and resistance is of crucial importance. Here we show that a yeast strain engineered to endogenously produce vitamin C exhibits an increased tolerance compared to the parental strain when exposed to acetic acid at moderately toxic concentrations, measured as viability on plates. Starting from this evidence, we investigated more deeply: (a) the nature and levels of reactive oxygen species (ROS); (b) the activation of enzymes that act directly as detoxifiers of reactive oxygen species, such as superoxide dismutase (SOD) and catalase, in parental and engineered strains during acetic acid stress. The data indicate that the engineered strain can better recover from stress by limiting ROS accumulation, independently from SOD activation. The engineered yeast can be proposed as a model for further investigating direct and indirect mechanism(s) by which an antioxidant can rescue cells from organic acid damage; moreover, these studies will possibly provide additional targets for further strain improvements.

The Population Dynamics of Nitrifiers in Ammonium‐Rich Systems

Non-optimal pH, dissolved oxygen concentration, the presence of toxic substances, or the influence of grazers are known to cause disturbances in nitrification. Because activated sludge is a mixture of different organisms, bacteria, and higher organisms, the stability of processes such as carbon removal, nitrification, denitrification, and dephosphatation depends on a range of interactions. These interactions occur both between and within trophic levels. Understanding of the ecology of microorganisms involved in bioprocesses is essential for effective control of startup and operation of a particular process. The aim of the study was to gain further insight into the dynamics of nitrifiers in activated sludge at various sludge ages while treating higher concentrations of ammonium. The results confirmed the importance of Nitrosococcus mobilis and Nitrobacter sp. as the dominant nitrifiers responsible for nitritation and nitratation, respectively, in the presence of unlimited ammonium. The size of the dominant bacteria colony was larger compared to the other species present and reached 25 microm. Problems with nitrification occurred in all high-ammonium loaded reactors. The dynamics of nitrifier population was monitored by oxygen uptake rate (OUR) using a test enabling the OUR measurement separately for ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). The results reveal the hypersensitivity of nitrifiers to the substrate and products of incomplete nitrification.

Impact of precipitation on the treatment of real ion-exchange brine using the H2-based membrane biofilm reactor

The H(2)-based membrane biofilm reactor (MBfR) was used to remove nitrate and perchlorate from real ion-exchange brine at two different salinities (30- and 50-g/L NaCl). Base production from nitrate reduction to N(2) gas caused the pH to increase, and this exacerbated precipitation of calcium and magnesium carbonates onto the MBfR fibers. The precipitates lowered the H(2) flux to the biofilm and caused a deterioration of denitrification performance that could be reversed by mild citric-acid washing. The addition of acid seems to be the only mechanism to avoid serious precipitation, membrane fouling, and non-optimal pH for denitrification.

Dynamic flux balance modeling of microbial co‐cultures for efficient batch fermentation of glucose and xylose mixtures

Sequential uptake of pentose and hexose sugars that compose lignocellulosic biomass limits the ability of pure microbial cultures to efficiently produce value-added bioproducts. In this work, we used dynamic flux balance modeling to examine the capability of mixed cultures of substrate-selective microbes to improve the utilization of glucose/xylose mixtures and to convert these mixed substrates into products. Co-culture simulations of Escherichia coli strains ALS1008 and ZSC113, engineered for glucose and xylose only uptake respectively, indicated that improvements in batch substrate consumption observed in previous experimental studies resulted primarily from an increase in ZSC113 xylose uptake relative to wild-type E. coli. The E. coli strain ZSC113 engineered for the elimination of glucose uptake was computationally co-cultured with wild-type Saccharomyces cerevisiae, which can only metabolize glucose, to determine if the co-culture was capable of enhanced ethanol production compared to pure cultures of wild-type E. coli and the S. cerevisiae strain RWB218 engineered for combined glucose and xylose uptake. Under the simplifying assumption that both microbes grow optimally under common environmental conditions, optimization of the strain inoculum and the aerobic to anaerobic switching time produced an almost twofold increase in ethanol productivity over the pure cultures. To examine the effect of reduced strain growth rates at non-optimal pH and temperature values, a break even analysis was performed to determine possible reductions in individual strain substrate uptake rates that resulted in the same predicted ethanol productivity as the best pure culture.

Genetic interactions among the Arl1 GTPase and intracellular Na+/H+ antiporters in pH homeostasis and cation detoxification

The roles of intracellular GTPase Arl1 and organellar cation/H(+) antiporters (Kha1 and Nhx1) in Saccharomyces cerevisiae tolerance to various stress factors were investigated and interesting new phenotypes of strains devoid of these proteins were found. The role of Arl1 GTPase in their tolerance to various cations is not caused by an altered plasma-membrane potential. Besides the known sensitivity of arl1 mutants to high temperature, we discovered their sensitivity to low temperature. We found for the first time that in the absence of Arl1p, Kha1p increases potassium, sodium and lithium tolerance, and can thus be categorized as an antiporter with broad substrate specificity. Kha1p also participates in the detoxification of undesired chemical compounds, pH regulation and growth at nonoptimal temperatures. Cells with the combined deletions of all three genes have considerable difficulty growing under nonoptimal conditions. We conclude that Arl1p, Kha1p and Nhx1p collaborate in survival strategies at nonoptimal pH, temperatures and cation concentrations, but work independent of each other.

Functional genomics of pH homeostasis in Corynebacterium glutamicum revealed novel links between pH response, oxidative stress, iron homeostasis and methionine synthesis

BackgroundThe maintenance of internal pH in bacterial cells is challenged by natural stress conditions, during host infection or in biotechnological production processes. Comprehensive transcriptomic and proteomic analyses has been conducted in several bacterial model systems, yet questions remain as to the mechanisms of pH homeostasis.ResultsHere we present the comprehensive analysis of pH homeostasis in C. glutamicum, a bacterium of industrial importance. At pH values between 6 and 9 effective maintenance of the internal pH at 7.5 ± 0.5 pH units was found. By DNA microarray analyses differential mRNA patterns were identified. The expression profiles were validated and extended by 1D-LC-ESI-MS/MS based quantification of soluble and membrane proteins. Regulators involved were identified and thereby participation of numerous signaling modules in pH response was found. The functional analysis revealed for the first time the occurrence of oxidative stress in C. glutamicum cells at neutral and low pH conditions accompanied by activation of the iron starvation response. Intracellular metabolite pool analysis unraveled inhibition of the TCA and other pathways at low pH. Methionine and cysteine synthesis were found to be activated via the McbR regulator, cysteine accumulation was observed and addition of cysteine was shown to be toxic under acidic conditions.ConclusionsNovel limitations for C. glutamicum at non-optimal pH values were identified by a comprehensive analysis on the level of the transcriptome, proteome, and metabolome indicating a functional link between pH acclimatization, oxidative stress, iron homeostasis, and metabolic alterations. The results offer new insights into bacterial stress physiology and new starting points for bacterial strain design or pathogen defense.

High activity of Mj HSP16.5 under acidic condition

Small heat shock proteins (sHSPs) exist ubiquitously among all organisms, with a variety of functions. All small heat shock proteins assemble into a native large oligomeric state containing 9－40 monomers. The sHSPs show chaperone-like activity to prevent the aggregation of nonnative proteins under stressful cellular conditions such as non-optimal temperatures, pH changes, osmotic pressure, and exposure to toxic chemicals. It was found that a common dimeric subunit of sHSPs might be the major active species, but whether the native large oligomeric state is only a storage state or a state crucial to its molecular chaperone activity is still under debate. The native large oligomeric state of the small heat shock protein from a hyperthermophilic methanarchaeon, Methanococcus jannaschii (Mj HSP 16.5), is a stable icositetramer, which is a symmetric hollow sphere that is very stable even at 85℃, and no small active subunit has been detected till now. Our results show that Mj sHSP 16.5 changes into small and active oligomeric state at pH 3, likely as octamers (average result) at 25℃, and dimers at 65℃. The dimer of Mj HSP 16.5 at pH 3.0 and 65℃ is very active and efficient, even 7-fold more efficient than the high-temperature-activated icositetramer at neutral pH. Monomer exchange can be observed between dimers of Mj HSP 16.5 at pH 3.0 and 65℃. These results not only demonstrate that the icositetramer structure of Mj sHSP16.5 is not necessary for its molecular chaperone activity, but also suggest that Mj sHSP16.5 is a very efficient chaperone acting at high temperature and under the acidic condition. Even though it is not clear whether the native environment of Methanococcus jannaschii is acidic or not, given its ability to excrete acidic compounds, it is likely that Methanococcus jannaschii will encounter acidic internal or external environments at high temperature. Our results demonstrate that Mj HSP 16.5 may help Methanococcus jannaschii to survive better under those extreme environmental conditions.

Ph-Dependent Assembly of DNA-Gold Nanoparticles Based on the i-Motif

Oligonucleotides containing stretches of 2 ′-deoxycytidine residues were immobilized on 15 nm gold nanoparticles. Under acidic pH conditions a reversible supramolecular assembly is formed, induced by the formation of the tetrameric i-motif structure. The replacement of 2 ′-deoxycytidine by 5-propynyl-2 ′-deoxycytidine (dC*) leads to novel i-motif structures. Oligonucleotides incorporating multiple residues of dC* were immobilized on 15 nm gold nanoparticles and are able to aggregate into i-motif structures even at non-optimal pH values.

Oligonucleotides forming an i-motif: the pH-dependent assembly of individual strands and branched structures containing 2′-deoxy-5-propynylcytidine

Non-branched and branched oligonucleotides incorporating consecutive runs of 2'-deoxy-5-propynylcytidine residues () instead of 2'-deoxycytidine () were synthesized. For this, phosphoramidite building blocks of 2'-deoxy-5-propynylcytidine () were prepared using acetyl, benzoyl or N,N-di-n-butylaminomethylidene protecting groups. The formation of the i-motif assemblies incorporating 2'-deoxy-5-propynylcytidine residues was confirmed by temperature-dependent CD- and UV-spectra as well as by ion-exchange chromatography. The low pK(a)-value of nucleoside (pK(a) = 3.3) compared to dC (pK(a) = 4.5) required strong acidic conditions for i-motif formation. Branched oligonucleotide residues with strands in a parallel orientation lead to a strong stabilization of the i-motif allowing aggregation even at non-optimal pH conditions (pH = 5). The immobilization of oligonucleotides incorporating multiple residues of on 15 nm gold nanoparticles generated DNA-gold nanoparticle conjugates which are able to aggregate into i-motif structures at pH 5.

Modification of optimal pH in l-arabinose isomerase from Geobacillus stearothermophilus for d-galactose isomerization

l-Arabinose isomerase from Geobacillus stearothermophilus (GSAI; EC 5.3.1.4) has been genetically evolved to increase the reaction rate toward d-galactose, which is not a natural substrate. To change the optimal pH of GSAI for d-galactose isomerization (pH optimum at 8.5), we investigated the single point mutations influencing the activity based on the sequences of the previously evolved enzymes. Among the seven point mutations found in the evolved enzymes, mutations at Val 408 and Asn 475 were determined to be highly influential mutation points for d-galactose isomerization activity. A random mutation was introduced into sites Val 408 and Asn 475 (X408V and X475N), and candidates were screened based on non-optimal pH conditions. Among the mutations of X408V and X475N, mutations of Q408V and R408V were selected. The optimal pH of the both mutations Q408V and R408V was shifted to pH 7.5. At the shifted optimal pH, the d-galactose isomerization activities of Q408V and R408V were 60 and 30% higher than that of the wild type at pH 8.5, respectively.

Phosphorus concentration and pH in decaying wood affect establishment of the red-listed moss Buxbaumia viridis

Many red-listed species grow on decaying wood in the boreal forest, and their persistence depends on dispersal to new patches. To investigate whether substrate quality could affect establishment and distribution of the red-listed moss Buxbaumia viridis (DC) Moug. &amp; Nestl., cultivation experiments as well as a field investigation of wood quality were performed. Spore germination was negatively affected by low pH and phosphorus (P) concentration in cultivation media, while nitrogen (N) concentration did not significantly affect germination. Results from the experiments were supported by the field investigation, where the probability of sporophyte occurrence increased with increasing pH. In addition, the interaction between substrate type (wood or humus) and P was significant. Occurrence of sporophytes was not significantly affected by N concentration in the wood. The results from the cultivation experiments and the field study imply that the safe site for germination and establishment of Buxbaumia viridis is either a substrate with continuously high moisture or a substrate with lower moisture but with increased pH and (or) P content, attained, e.g., by throughfall and litterfall from deciduous trees, and that non-optimal pH, P, and moisture conditions could restrict establishment and distribution of the species.Key words: bryophyte, decaying wood, germination, protonema, safe site, substrate quality.