Bacteria and fungi can form a range of physical associations that depend on various modes of molecular communication for their development and functioning. These bacterial-fungal interactions often result in changes to the pathogenicity or the nutritional influence of one or both partners toward plants or animals (including humans). They can also result in unique contributions to biogeochemical cycles and biotechnological processes. Thus, the interactions between bacteria and fungi are of central importance to numerous biological questions in agriculture, forestry, environmental science, food production, and medicine. Here we present a structured review of bacterial-fungal interactions, illustrated by examples sourced from many diverse scientific fields. We consider the general and specific properties of these interactions, providing a global perspective across this emerging multidisciplinary research area. We show that in many cases, parallels can be drawn between different scenarios in which bacterial-fungal interactions are important. Finally, we discuss how new avenues of investigation may enhance our ability to combat, manipulate, or exploit bacterial-fungal complexes for the economic and practical benefit of humanity as well as reshape our current understanding of bacterial and fungal ecology.

Bacterial-Fungal Interactions: Hyphens between Agricultural, Clinical, Environmental, and Food Microbiologists

Microorganisms are able to utilize nitrogen (N) from a wide range of organic and mineral compounds. In this paper, we review the current knowledge about the regulation of the enzyme systems involved in the acquisition of N and propose a conceptual model on the factors affecting the relative importance of organic and mineral N uptake. Most of the N input into soil is in the form of polymers, which first have to be broken down into smaller units by extracellular enzymes. The small organic molecules released by the enzymes can then be taken up directly or degraded further and the N taken up as ammonium (NH4+). When NH4+ is available at high concentrations, the utilization of alternative N sources, such as nitrate (NO3−) and organic molecules, is generally repressed. In contrast, when the NH4+ availability is low, enzyme systems for the acquisition of alternative N sources are de-repressed and the presence of a substrate can induce their synthesis. These mechanisms are known as N regulation. It is often assumed that most organic N is mineralized to NH4+ before uptake in soil. This pathway is generally known as the mineralization-immobilization-turnover (MIT) route. An advantage of the MIT route is that only one transporter system for N uptake is required. However, organic N uptake has the advantage that, in addition to N, it supplies energy and carbon (C) to sustain growth. Recent studies have shown that the direct uptake of organic molecules can significantly contribute to the N nutrition of soil microorganisms. We hypothesize that the relative importance of the direct and MIT route during the decomposition of residues is determined by three factors, namely the form of N available, the source of C, and the availability of N relative to C. The regulation system of soil microorganisms controls key steps in the soil N cycle and is central to determining the outcome of the competition for N between soil microorganisms and plants. More research is needed to determine the relative importance of the direct and MIT route in soil as well as the factors affecting the enzyme systems required for these two pathways.

Pathways of nitrogen utilization by soil microorganisms - a review.

Electrochemical biosensor applications of polysaccharides chitin and chitosan.

There has been many recent studies on the use of microbial antagonists to control diseases incited by soilborne and airborne plant pathogenic bacteria and fungi, in an attempt to replace existing methods of chemical control and avoid extensive use of fungicides, which often lead to resistance in plant pathogens. In agriculture, plant growth-promoting and biocontrol microorganisms have emerged as safe alternatives to chemical pesticides. Streptomyces spp. and their metabolites may have great potential as excellent agents for controlling various fungal and bacterial phytopathogens. Streptomycetes belong to the rhizosoil microbial communities and are efficient colonizers of plant tissues, from roots to the aerial parts. They are active producers of antibiotics and volatile organic compounds, both in soil and in planta, and this feature is helpful for identifying active antagonists of plant pathogens and can be used in several cropping systems as biocontrol agents. Additionally, their ability to promote plant growth has been demonstrated in a number of crops, thus inspiring the wide application of streptomycetes as biofertilizers to increase plant productivity. The present review highlights Streptomyces spp.-mediated functional traits, such as enhancement of plant growth and biocontrol of phytopathogens.

https://www.mdpi.com/1422-0067/19/4/952/pdf

Plant Growth Promoting and Biocontrol Activity of Streptomyces spp. as Endophytes.

Two centuries after the discovery of chitin, it is widely accepted that this biopolymer is an important biomaterial in many aspects. Numerous studies on chitin have focused on its biomedical applications. In this review, various aspects of chitin research including sources, structure, biosynthesis, chitinolytic enzyme, chitin binding protein, genetic engineering approach to produce chitin, chitin and evolution, and a wide range of applications in bio- and nanotechnology will be dealt with.

Chitin Research Revisited

Chitin is among the most abundant biomass present on Earth. Chitinase plays an important role in the decomposition of chitin and potentially in the utilization of chitin as a renewable resource. During the previous decade, chitinases have received increased attention because of their wide range of applications. Chito-oligomers produced by enzymatic hydrolysis of chitin have been of interest in recent years due to their broad applications in medical, agricultural, and industrial applications, including antibacterial, antifungal, hypocholesterolemic, and antihypertensive activity, and as a food quality enhancer. Microorganisms, particularly bacteria, form one of the major sources of chitinase. In this article, we have reviewed some of the chitinases produced by bacterial systems that have gained worldwide research interest for their diverse properties and potential industrial uses.

Bacterial chitinases: properties and potential.

Biological control of phytopathogenic fungi and insects continues to inspire the research and development of environmentally friendly bioactive alternatives. Potentially lytic enzymes, chitinases can act as a biocontrol agent against agriculturally important fungi and insects. The cell wall in fungi and protective covers, i.e. cuticle in insects shares a key structural polymer, chitin, a β-1,4-linked N-acetylglucosamine polymer. Therefore, it is advantageous to develop a common biocontrol agent against both of these groups. As chitin is absent in plants and mammals, targeting its metabolism will signify an eco-friendly strategy for the control of agriculturally important fungi and insects but is innocuous to mammals, plants, beneficial insects and other organisms. In addition, development of chitinase transgenic plant varieties probably holds the most promising method for augmenting agricultural crop protection and productivity, when properly integrated into traditional systems. Recently, human proteins with chitinase activity and chitinase-like proteins were identified and established as biomarkers for human diseases. This review covers the recent advances of chitinases as a biocontrol agent and its various applications including preparation of medically important chitooligosaccharides, bioconversion of chitin as well as in implementing chitinases as diagnostic and prognostic markers for numerous diseases and the prospect of their future utilization.

Chitinases: in agriculture and human healthcare

The actinomycetes Streptomyces violaceusniger showed strong antagonistic activity against various tested wood rotting fungi. An extracellular chitinase, produced by antagonistic S. violaceusniger MTCC 3959, was purified as follows: ammonium sulfate precipitation, chitin affinity and chromatographic separation of Q Sepharose. The molecular mass of the purified chitinase was estimated as 56.5 kDa by SDS-PAGE. Chitinase was optimally active at pH of 5.0 and 50 °C. It retained almost 100% activity at pH 5.0 and also had high thermal tolerance at 50 °C. Enzyme activity was inhibited by Hg(2+) and Ag(+) cations, but was neither substantially inhibited by K(+) cation nor by chelating agent EDTA. The apparent Km and Vmax at 37 °C were 0.1426 mM and 6.6 U/mg, respectively using pNP-(GlcNAc)2 as substrate. The 56.5 kDa chitinase of strain MTCC 3959 represented an exo-type activity. The purified chitinase was further identified by MALDI-TOF. The results of peptide mass fingerprinting showed that 10 tryptic peptides of the chitinase were identical to the chitinase C from Streptomyces albus J1074 (GenBank Accession No. gi|239982330). The sequence of N-terminal amino acid (AA) of the chitinase was determined to be G-D-G-T-G-P-G-P-G-P.

Purification and characterization of an extracellular chitinase from antagonistic Streptomyces violaceusniger

Globalization of the food trade requires precise and exact information about the origin, methods of production, transformation technologies, authentication, and the traceability of foodstuffs. New ...

DNA barcoding: a modern age tool for detection of adulteration in food

An actinomycetes isolate of Loktak Lake soil, designated as MT7, was characterized and identified as Streptomyces sp. based on fatty acid methyl ester and 16S ribosomal RNA gene analysis. Streptomyces sp. MT7 showed strong and broad spectrum antagonism towards seven out of eight tested wood-rotting fungi. Strain MT7 secretes three vital fungal cell wall lytic enzymes, i.e. chitinase, β-1,3-glucanase, and protease, and siderophores. Extracellularly produced mycolytic enzymes lost their antifungal activity completely after treatment with proteinase K and heat, indicating that the tested antifungal metabolites are heat-sensitive and proteinaceous in nature. Extracellular fluid (ECF) and its organic solvent extract also exhibited potential antagonism towards the tested wood-rotting fungi. Antifungal metabolites were characterized as polyene in nature. Biocontrol traits like co-production of cell wall lytic enzymes and antifungal secondary metabolites including siderophores by Streptomyces sp. MT7 suggests that it could be employed as a potential biocontrol agent against wood-rotting basidiomycetes.

Anand Nagpure

Papers

Bacterial chitinases: properties and potential.

Chitinases: in agriculture and human healthcare

Purification and characterization of an extracellular chitinase from antagonistic Streptomyces violaceusniger

DNA barcoding: a modern age tool for detection of adulteration in food

Isolation and characterization of chitinolytic Streptomyces sp. MT7 and its antagonism towards wood-rotting fungi