Understanding which factors affect the process of leaf litter decomposition is crucial if we are to predict changes in the functioning of stream ecosystems as a result of human activities. One major activity with known consequences on streams is agriculture, which is of particular concern in tropical regions, where forests are being rapidly replaced by crops. While pesticides are potential drivers of reduced decomposition rates observed in agricultural tropical streams, their specific effects on the performance of decomposers and detritivores are mostly unknown. We used a microcosm experiment to examine the individual and joint effects of an insecticide (chlorpyrifos) and a fungicide (chlorothalonil) on survival and growth of detritivores (Anchytarsus, Hyalella and Lepidostoma), aquatic hyphomycetes (AH) sporulation rate, taxon richness, assemblage structure, and leaf litter decomposition rates. Our results revealed detrimental effects on detritivore survival (which were mostly due to the insecticide and strongest for Hyalella), changes in AH assemblage structure, and reduced sporulation rate, taxon richness and microbial decomposition (mostly in response to the fungicide). Total decomposition was reduced especially when the pesticides were combined, suggesting that they operated differently and their effects were additive. Importantly, effects on decomposition were greater for single-species detritivore treatments than for the 3-species mixture, indicating that detritivore species loss may exacerbate the consequences of pesticides of stream ecosystem functioning.

Phytophthora capsici, an economically devastating oomycete pathogen, causes devastating disease epidemics on a wide range of vegetable plants and pose a grave threat to global vegetables production. Heavy metals and acid pH are newly co-occurring stresses to soil micro-organisms, but what can be expected for mycelia growth and virulence and how they injure the oomycetes (especially P. capsici) remains unknown. Here, the effects of different heavy metals (Cu²⁺, Cr²⁺, and Hg²⁺) on mycelia growth and virulence were investigated at different pHs (4.0 vs. 7.0) and the plausible molecular and physiological mechanisms were analyzed. In the present study, we compared the effective inhibition of different heavy metals (Cu²⁺, Cr²⁺, and Hg²⁺) and acid pH on a previously genome sequenced P. capsici virulent strain LT1534. Both stress factors independently affected its mycelia growth and sporulation. Next, we investigated whether ROS participated in the pH-inhibited mycelial growth, finding that the ROS scavenger, catalase (CAT), significantly inhibited the acid pH-induced ROS in mycelia. Additionally, because MAPK specially transmits different stress responsive signals in environment into cells, we employed CAT and a p38-MAPK pathway inhibitor to investigate ROS and p38-MAPK roles in heavy metal-inhibited mycelia growth at different pHs (4.0 vs. 7.0), finding that they significantly inhibited growth. Furthermore, ROS and p38-MAPK influenced the heavy metal-induced TBARS content, total antioxidant capacity (TAC), and CAT activity at different pHs, and also reduced the expression of infection-related laccases (PcLAC2) and an effector-related protein (PcNLP14). We propose that acid pH stress accelerates how heavy metals inhibit mycelium growth, sporulation, and virulence change in P. capsici, and posit that ROS and p38-MAPK function to regulate the molecular and physiological mechanisms underlying this toxicity. Although these stresses induce molecular and physiological challenges to oomycetes, much remains to be known the mechanisms dedicated to resolve these environmental stresses.

The Pestalotiopsis sp. genus comprises filamentous fungi whose species present both pathogenic and clinical-industrial importance. The cultivation and production of bivalve molluscs in regions of Rio de Janeiro is lucrative both artisanally and industrially, as the climate, geography and water quality favor the practice of this activity throughout the year at reduced costs, making the region competitive in the national market. The aim of this study was to isolate and identify filamentous fungi associated with the internal tissue anatomy of bivalve molluscs (Perna perna) from mariculture farms. Samples collected from BEMAR marine farms were dissected and transferred to 1% hypochlorite, washed in sterile distilled water and sown on Petri dishes containing potato dextrose agar (BDA). After four days, a white colony, displaying vigorous mycelium, cotton-like with abundant sporulation and black conidia masses was isolated. Observations concerning vegetative and reproductive structures were performed by microcultures stained with Amann's Lactophenol andCotton Blue. Micromorphology analyses indicated spindle and septated conidia, with two to three apical filiform appendages and a short basal pedicel. The result indicates that bivalve mollusks may be bioindicators for the presence of Pestalotiopsis sp; associated with water transport, possibly due to diluted sediments in the medium. No infectious processes or lesions in the processed material were observed. This is, to the best of our knowledge, the first report of Pestalotiopsis sp; in Perna perna mytilids.

Composting process of residual organic material generates considerable amounts of liquid leachate which contains high organic load. This waste stream can be considered as potential nutrient source to support microbial growth. In the present work, the utilization of compost leachate as fermentation substrate for Bacillus species production was studied. The physicochemical properties of the leachate and two co-substrates (residual yeast and whey permeate) were determined. The characterization of leachate showed that it is a potential source of carbon, but its nitrogen content may limit the bacterial growth. In order to determine a good recipe of culture medium for fermentation of individual strains of Bacillus species, leachate was added with yeast and whey permeate. Raw and diluted leachates with and without amendments were tested in shake-flask fermentation assays. Results showed that Bacillus sp. grew better in diluted leachate than in raw leachate. When co-substrates were added, the growth was improved and the sporulation rate also increased. Since the aim was to produce plant growth–promoting bacteria, one of the objectives of fermentation assays was the production of viable bacteria when Bacillus sp. arrives to soil as component of a fertilizer. For this reason, the obtention of sporulated Bacillus cells was desired. The highest sporulation rate was obtained with co-substrates, inducing more than 89% of vegetative cells to develop spores. This approach of leachate valorization will produce economical benefits reducing the volume of leachate waste to be treated, as well as contribute in a cost-effective production of biological amendments in a circular economy mode.

This study was aimed at studying the effect of heavy metals and arsenic on the survival and biofilm formation of some saprotrophic microorganisms: Bacillus megaterium var. phosphaticum, Bacillus mucilaginosus, Pectobacterium carotovorum, and Escherichia coli. As a source of heavy metals and arsenic, we used aqueous solutions of NaAsO₂, Cd(CH₃COO)₂, and Pb(NO₃)₂ (2.5, 25, 250 mg L⁻¹). The cultures in the liquid medium had different resistance to the toxicants under study: B. megaterium > B. mucilaginosus > P. carotovorum > E. coli. The toxicity of the tested solutions of heavy metals and arsenic for microorganisms can be arranged (decreasing toxicity) as follows: cadmium acetate > lead nitrate > sodium metaarsenite. These experiments revealed some regularities related to the mechanisms of toxic effect of As, Pb, and Cd solutions on the formation of biofilms of soil bacteria, changes in bacterial cellular forms, and their survival. Bacillus megaterium strain was the most resistant to high As concentrations and was able to influence the formation of highly structured colonies of bacterial cells with the honeycomb-like structure. The immobilization of heavy metals can be achieved due to their binding into strong compounds with the matrix substances of biofilms and polymeric organic compounds formed during the sporulation of rhizobacteria. It can increase the resistance of bacteria to high concentrations of heavy metals and arsenic. The results obtained can be of great practical importance in the development of biotechnologies related to soil bioremediation, in the field of nanotechnology, crop production, and medicine.

The bioactivity of three kinds of multi-walled carbon nanotubes (MWCNT) towards the conidia of entomopathogenic fungus Isaria fumosorosea was examined in an in vitro study. Commercial—raw and functionalized—carboxylated MWCNT were applied. A fungal conidia suspension was placed in contact with dispersed MWCNT over different time-periods. After contact with the nanomaterial, the conidia were cultured on dishes and both the linear vegetative mycelium growth and the sporulation and germination of the spores derived from the culture were investigated. Also, the pathogenicity of the conidia after contact with MWCNT was examined in relation to test larvae. No fungistatic activity of MWCNT relative to I. fumosorosea conidia was demonstrated. Conidia contact with MWCNT resulted in the following changes in vital processes in the subsequent culture compared to the control standard culture: (1) raw MWCNT limited mycelium inoculation, but the growth rate observed later in the log-phase was more intense; (2) after 24-h conidia contact with all MWCNT types, the mycelium sporulated the most intensively; longer contact resulted in sporulation process limitation. Germination of conidia after contact with the MWCNT was not significantly modified. Raw MWCNT potentiated conidia pathogenicity towards test insects. It was observed that carboxylation of MWCNT reduces the bioactivity of this nanomaterial towards the investigated conidia.

This study evaluated the effect of lead (Pb(II)), zinc (Zn(II)) and copper (Cu(II)) on growth and sporulation of four Halophytophthora species (Halophytophthora vesicula, Halophytophthora elongata, Halophytophthora spinosa var. lobata, and an oogonia-producing Halophytophthora sp.) isolated from different mangrove sites in Taiwan. Results show that all isolates grew well or even better at 1 ppm concentration of the heavy metals tested. Growth of all test isolates was totally inhibited at 500 ppm, except for H. spinosa var. lobata exposed to Zn(II). For sporulation, all isolates produced moderate to abundant zoosporangia or oogonia at 1 ppm Pb(II) and Zn(II). Production of zoosporangia by H. vesicula, H. elongata and H. spinosa var. lobata was significantly affected or totally inhibited at 1 ppm Pb(II) and Zn(II) and all concentrations of Cu(II). Abnormal oogonia were produced by Halophytophthora sp. at 10 ppm Cu(II) and 100 ppm of the three heavy metals. In general, Cu(II) and Zn(II) were found to be the most toxic, and the least toxic was Pb(II). H. spinosa var. lobata was the most tolerant to all the heavy metals, while H. vesicula and H. elongata were the most sensitive. Results of this study shows that increased concentrations of Pb(II), Cu(II), and Zn(II) in the mangrove environment can significantly affect growth and impair normal reproduction of Halophytophthora species.

The stored grain insects cause great damage to grains under storage conditions. Synthetic insecticides and fumigants are considered as key measures to control these stored grain insect pests. However, the major issue with these chemicals is grain contamination with chemical residues and development of resistance by insect pests to these chemicals. Biological control is considered as a potential alternative to chemical control especially with the use of pathogens, alone or in combination with selective insecticides. The present study was conducted to evaluate the synergism of Metarhizium anisopliae with diatomaceous earth (DE) and thiamethoxam against four insect pests on the stored wheat grains. In the first bioassay, the M. anisopliae was applied at 1.4 × 10⁴ and 1.4 × 10⁶conidia/ml alone and in integration with two concentrations (250 and 500 ppm) of tested DE. The tested fungus when combined with DE and thiamethoxam possessed synergistic impact as compared to their individual efficacy. Adult mortality increased with respect to increased exposure interval and doses. In the second bioassay, M. anisopliae was applied at 1.4 × 10⁴ conidia/ml individually and in combination with three concentrations (0.50, 0.75, and 1.00 ppm) of thiamethoxam. Results concluded that M. anisopliae integrated with DE and thiamethoxam provides more effective control of stored grain insect pests.

Abiotic stress can influence the interactions between a pathogen and its host. In this paper, we analyzed the effects of salicylic acid (SA) and pH on the morphological development and pathogenicity of Magnaporthe oryzae, the pathogen that causes rice (Oryza sativa) blast. A strain of rice blast that overexpresses biotrophy-associated secreted protein 1 (BAS1) and a wild-type (WT) strain were pretreated with different levels of pH and different concentrations of SA to analyze M. oryzae colony growth, sporulation, spore germination, dry weight of hypha, and appressorium formation. Disease incidence and the expression of defense-related genes in infected rice were analyzed after pretreatment with pH 5.00 or pH 8.00 and 200 μM SA. The results showed that both SA and pH had some influence on morphological development, including sporulation and appressorium formation of the BAS1-overexpression strain. In the 200 μM SA pretreatment, there was a lower incidence of disease and higher expression levels of the rice defense-related genes PR1a, PAL, HSP90, and PR5 on leaves inoculated with the BAS1-overexpession strain compared with the WT strain, whereas, LOX2 appeared to be downregulated in the BAS1-overexpession strain compared with the WT. In both pH treatments, disease incidence and expression of HSP90 were higher and the expression of PR1a and PR10a and LOX2 and PAL was lower in leaves inoculated with the BAS1-overexpression strain compared with leaves inoculated with the WT strain. We conclude that SA and pH affect morphological development of the BAS1-overexpression blast strain, but that these factors have little influence on the pathogenicity of the strain, indicating that BAS1-overexpression may have enhanced the tolerance of this rice blast strain to abiotic stressors. This work suggests new molecular mechanisms that exogenous SA and pH affect the interactions between M. oryzae and rice.