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Soil moisture controls microbial activity and soil carbon cycling. Because microbial activity decreases as soils dry, decomposition of soil organic matter (SOM) is thought to decrease with increasing drought length. Yet, microbial biomass and a pool of water-extractable organic carbon (WEOC) can increase as soils dry, perhaps implying microbes may continue to break down SOM even if drought stressed. Here, we test the hypothesis that WEOC increases as soils dry because exoenzymes continue to break down litter, while their products accumulate because they cannot diffuse to microbes. To test this hypothesis, we manipulated field plots by cutting off litter inputs and by irrigating and excluding precipitation inputs to extend or shorten the length of the dry season. We expected that the longer the soils would remain dry, the more WEOC would accumulate in the presence of litter, whereas shortening the length of the dry season, or cutting off litter inputs, would reduce WEOC accumulation. Lastly, we incubated grass roots in the laboratory and measured the concentration of reducing sugars and potential hydrolytic enzyme activities, strictly to understand the mechanisms whereby exoenzymes break down litter over the dry season. As expected, extending dry season length increased WEOC concentrations by 30% above the 108 μg C/g measured in untreated plots, whereas keeping soils moist prevented WEOC from accumulating. Contrary to our hypothesis, excluding plant litter inputs actually increased WEOC concentrations by 40% above the 105 μg C/g measured in plots with plants. Reducing sugars did not accumulate in dry senesced roots in our laboratory incubation. Potential rates of reducing sugar production by hydrolytic enzymes ranged from 0.7 to 10 μmol·g−1·h−1 and far exceeded the rates of reducing sugar accumulation (̃0.001 μmol·g−1·h−1). Our observations do not support the hypothesis that exoenzymes continue to break down litter to produce WEOC in dry soils. Instead, we develop the argument that physical processes are more likely to govern short-term WEOC dynamics via slaking of microaggregates that stabilize SOM and through WEOC redistribution when soils wet up, as well as through less understood effects of drought on the soil mineral matrix.

Soil carbon cycling and ecosystem functioning can strongly depend on how microbial communities regulate their metabolism and adapt to changing environmental conditions to improve their fitness. Investing in extracellular enzymes is an important strategy for the acquisition of resources, but the principle behind the trade-offs between enzyme production and growth is not entirely clear. Here we show that the enzyme production rate per unit biomass may be regulated in order to maximize the biomass specific growth rate. Based on this optimality hypothesis, we derive mathematical expressions for the biomass specific enzyme production rate and the microbial carbon use efficiency, and verify them with experimental observations. As a result of this analysis, we also find that the optimal enzyme production rate decays hyperbolically with the soil organic carbon content. We then show that integrating the optimal extracellular enzyme production into soil microbial carbon models may change considerably soil carbon projections under global warming, underscoring the need to improve parameterization of microbial processes.

The contamination of agricultural products with mycotoxins causes risks to animal and human health and severe economic losses. Mycotoxicoses can be reduced by preventing fungal infection using chemical and biological approaches. The chemical strategies can release toxic molecules; therefore, strategies for biological control are being evaluated, such as using nontoxic fungi and their metabolites. This work evaluated the effect of exoenzymes produced by the beneficial fungus Trichoderma afroharzianum strain T22 in degrading Aflatoxin B1 (AFB1) and Ochratoxin A (OTA). The ability of Trichoderma to produce hydrolases was stimulated by using different inducing substrates. The highest AFB1 and OTA degradation activity was obtained using a medium containing lyophilized mushrooms and crude fiber. The T. afroharzianum T22’s ability to reduce mycotoxins may be attributed to peroxidase enzymes. This study showed that T.afroharzianum strain T22 or its peroxidase supplementation could represent a sustainable strategy for the degradation of AFB1 and OTA in feed and food products.

High atmospheric nitrogen (N) deposition is expected to impair phosphorus (P) nutrition of temperate forest ecosystems. We examined N and P cycling in organic soil horizons of temperate forests exposed to long-term N addition in the northeastern USA and Scandinavia. We determined N and P concentrations, enzyme activities and net N and P mineralization rates in organic soil horizons of two deciduous (Harvard Forest, Bear Brook) and two coniferous (Klosterhede, Gårdsjön) forests which had received experimental inorganic N addition between 25 and 150 kg N ha⁻¹ year⁻¹ for more than 25 years. Long-term N addition increased the activity of phosphatase (+ 180%) and the activity of carbon (C)- and N-acquiring enzymes (cellobiohydrolase: + 70%, chitinase: + 25%). Soil N enrichment increased the N:P ratio of organic soil horizons by up to 150%. In coniferous organic soil horizons, net N and P mineralization were small and unaffected by N addition. In deciduous organic soil horizons, net N and P mineralization rates were significantly higher than at the coniferous sites, and N addition increased net N mineralization by up to 290%. High phosphatase activities concomitant with a 40% decline in P stocks of deciduous organic soil horizons indicate increased plant P demand. In summary, projected future global increases in atmospheric N deposition may induce P limitation in deciduous forests, impairing temperate forest growth.

The aim of this study was to devise a method to protect Chinese cabbage (Brassica chinensis) and lettuce (Lactuca sativa) from bacterial-disease-induced damage during storage. Thus, the potential of rhapontigenin as a quorum sensing (QS) inhibitor against Pectobacterium carotovorum subsp. carotovorum (P. carotovorum) was evaluated. The QS inhibitory effects of rhapontigenin were confirmed by significant inhibition of the production of violacein in Chromobacterium violaceum CV026 (C. violaceum, CV026). The inhibitory effects of rhapontigenin on the motility, exopolysaccharide (EPS) production, biofilm formation and virulence–exoenzyme synthesis of P. carotovorum were investigated. Acyl-homoserine lactones (AHLs) were quantified using liquid chromatography–mass spectrometry (LC–MS). The inhibitory effects of rhapontigenin on the development of biofilms were observed using fluorescence microscopy and scanning electron microscopy (SEM). A direct-inoculation assay was performed to investigate the QS inhibitory effects of rhapontigenin on P. carotovorum in Chinese cabbage and lettuce. Our results demonstrated that rhapontigenin exhibited significant inhibition (p < 0.05) of the motility, EPS production, biofilm formation, virulence–exoenzyme synthesis and AHL production of P. carotovorum. Additionally, the result of the direct-inoculation assay revealed that rhapontigenin might provide vegetables with significant shelf-life extension and prevent quality loss by controlling the spread of soft-rot symptoms. Consequently, the study provided a significant insight into the potential of rhapontigenin as a QS inhibitor against P. carotovorum.

Introduction: The emergence of resistance is a major public health and clinical issue, particularly in pathogens causing nosocomial infections. Recently, there is the emergence of Pseudomonas aeruginosa resistance to different broad-spectrum antibiotics. Methodology: The current study was designed to find out the prevalence of multi-drug resistant (MDR) P. aeruginosa in burn patients, the antibiotic susceptibility pattern of MDR Pseudomonas, and to determine the Minimum Inhibitory Concentration (MIC) of the effective antimicrobials. The assessment of virulence genes (exoT, exoS, exoY and exoU) was also achieved through PCR. In the current study wound swabs were collected from 160 burn patients from two burn units (MTI-Govt. Lady Reading Hospital and MTI-Khyber Teaching Hospital). Results: Out of these 160 samples, 26 samples (16.25%) were positive for P. aeruginosa. Per patients, one isolate was included in the current study. Antibiotic susceptibility pattern showed all P. aeruginosa isolates were 100% resistant to amoxicillin-clavulanic acid, 84.62% resistance to Cefepime, and Ceftazidime, and 76.92% resistance to Amikacin, Aztreonam, and Ciprofloxacin. Whereas the lowest resistance was observed to Imipenem and Piperacillin-Tazobactam (53.85%), Colistin Sulfate (23.08%), and Polymyxin-B (15.38%). Regarding the prevalence of MDR, 22 (84.61%) isolates out of 26 were found to be MDR-P. aeruginosa. For MDR-P. aeruginosa, the MIC range was 1-2 µg/mL against Polymyxin-B, 2-8 µg/mL against Colistin sulfate, 16-1024 µg/mL against Imipenem and 128-1024 µg/mL against Piperacillin-Tazobactam. 100% of the isolates carried exoT, 88.46% carried exoY, and 57.69% and 38.46% carried exoU and exoS, respectively. Conclusions: These findings further emphasize the need for antibiotic discipline and to follow the recommended hospital antibiotic policy to prevent the proliferation of MDR strains of P. aeruginosa in the community.

Endophytic fungi in medicinal plants aid in producing useful therapeutic compounds and enzymes. Among the most useful enzymes are cellulases. However, cellulase enzyme production in endophytic fungi of Azadirachta indica and Aloe secundiflora has not been comprehensively explored. The objective of this study was to; isolate and identify endophytic fungi from the leaves of young and mature plants of A. indica and A. secundiflora , determine colonization frequency of the endophytic fungi, and evaluate and optimize the cellulase production by the endophytic fungi on maize cob media. Eleven fungal endophytic isolates were obtained from the leaves of both A. secundiflora and A. indica, collected in Kitui and Kiambu Counties in total: Six from Kitui County and five from Kiambu County. Penicillium Sp. had highest colonization frequency in Kitui, while Candida sp. had highest in Kiambu. For enzyme optimization, isolates Candida boidinii , Galactomyces candidum , and Candida stellimalicola produced the highest amounts of Fpases and endoglucanases on third, sixth and ninth days. High exoglucanase producers were Colletotrichum gloeosporioides , Galactomyces candidum , and Candida stellimalicola . The endophytic communities within the leaves of A. indica and A. secundiflora are diverse. Maize cob agrowaste media can be used to cultivate the production of cellulases successfully in fungal endophytic isolates of A. indica and A. secundiflora . The study concluded that the endophytes of A. indica and A. secundiflora can be harnessed and optimized to secrete cellulase enzymes for commercial use, and especially isolates G. candidum and C. stellimalicola which yield significantly high amounts of total cellulases, endoglucanases and exoglucanases.

Penicillin-binding proteins (PBPs) are considered essential for bacterial peptidoglycan biosynthesis and cell wall assembly. Clavibacter michiganensis is a representative Gram-positive bacterial species that causes bacterial canker in tomato. pbpC plays a significant role in maintaining cell morphological characteristics and stress responses in C. michiganensis. The current study demonstrated that the deletion of pbpC commonly enhances bacterial pathogenicity in C. michiganensis and revealed the mechanisms through which this occurs. The expression of interrelated virulence genes, including celA, xysA, xysB, and pelA, were significantly upregulated in △pbpC mutants. Compared with those in wild-type strains, exoenzyme activities, the formation of biofilm, and the production of exopolysaccharides (EPS) were significantly increased in △pbpC mutants. It is noteworthy that EPS were responsible for the enhancement in bacterial pathogenicity, with the degree of necrotic tomato stem cankers intensifying with the injection of a gradient of EPS from C. michiganensis. These findings highlight new insights into the role of pbpC affecting bacterial pathogenicity, with an emphasis on EPS, advancing the current understanding of phytopathogenic infection strategies for Gram-positive bacteria.

Background and aims Bacterial Non-Specific Acid Phosphatase (NSAP) enzymes are capable of dephosphorylating diverse organic phosphoesters but are rarely studied: their distribution in natural and managed environments is poorly understood. The aim of this study was to generate new insight into the environmental distribution of NSAPs and establish their potential global relevance to cycling of organic phosphorus. Methods We employed bioinformatic tools to determine NSAP diversity and subcellular localization in microbial genomes; used the corresponding NSAP gene sequences to census metagenomes from diverse ecosystems; studied the effect of long-term land management upon NSAP diversity and abundance. Results Periplasmic class B NSAPs are poorly represented in marine and terrestrial environments, reflecting their association with enteric and pathogenic bacteria. Periplasmic class A and outer membrane-associated class C NSAPs are cosmopolitan. NSAPs are more abundant in marine than terrestrial ecosystems and class C more abundant than class A genes, except in an acidic peat where class A genes dominate. A clear effect of land management upon gene abundance was identified. Conclusions NSAP genes are cosmopolitan. Class C genes are more widely distributed: their association with the outer-membrane of cells gives them a clear role in the cycling of organic phosphorus, particularly in soils.

Candidate phylum Saccharibacteria (former TM7) are abundant and widespread in nature, but little is known about their ecophysiology and detailed phylogeny. In this study phylogeny, morphology and ecophysiology of Saccharibacteria were investigated in activated sludge from nine wastewater treatment plants (WWTPs) from Japan and Denmark using the full-cycle 16S rRNA approach in combination with microautoradiography (MAR) and fluorescence in situ hybridization (FISH). Phylogenetic analysis showed that Saccharibacteria from all WWTPs were evenly distributed within subdivision 1 and 3 and in a distinct phylogenetic clade. Three probes were designed for the distinct saccharibacterial groups, and revealed morphotypes representing thin filaments, thick filaments and rods/cocci. MAR-FISH results showed that most probe-defined Saccharibacteria utilized glucose under aerobic-, nitrate reducing- and anaerobic conditions. Some Saccharibacteria also utilized N-acetylglucosamine, oleic acid, amino acids and butyrate, which are not predicted from available genomes so far. In addition, some filamentous Saccharibacteria exhibited β-galactosidase and lipase activities determined using a combination of enzyme-labeled fluorescence and FISH (ELF-FISH). No uptake of acetate, propionate, pyruvate, glycerol and ethanol was observed. These results indicate that Saccharibacteria is a phylogenetically diverse group and play a role in the degradation of various organic compounds as well as sugar compounds under aerobic-, nitrate reducing- and anaerobic conditions. Candidatus Saccharibacteria in activated sludge are phylogenetically diverse and utilize oleic acid, amino acids,and N-acetylglucosamine as well as glucose as the carbon sources. Graphical Abstract Figure. Candidatus Saccharibacteria in activated sludge are phylogenetically diverse and utilize oleic acid, amino acids,and N-acetylglucosamine as well as glucose as the carbon sources.