Production of Metabolites as Bacterial Responses to the Marine Environment

Abstract

Bacteria in marine environments are often under extreme conditions of e.g., pressure, temperature, salinity, and depletion of micronutrients, with survival and proliferation often depending on the ability to produce biologically active compounds. Some marine bacteria produce biosurfactants, which help to transport hydrophobic low water soluble substrates by increasing their bioavailability. However, other functions related to heavy metal binding, quorum sensing and biofilm formation have been described. In the case of metal ions, bacteria developed a strategy involving the release of binding agents to increase their bioavailability. In the particular case of the Fe3+ ion, which is almost insoluble in water, bacteria secrete siderophores that form soluble complexes with the ion, allowing the cells to uptake the iron required for cell functioning. Adaptive changes in the lipid composition of marine bacteria have been observed in response to environmental variations in pressure, temperature and salinity. Some fatty acids, including docosahexaenoic and eicosapentaenoic acids, have only been reported in prokaryotes in deep-sea bacteria. Cell membrane permeability can also be adapted to extreme environmental conditions by the production of hopanoids, which are pentacyclic triterpenoids that have a function similar to cholesterol in eukaryotes. Bacteria can also produce molecules that prevent the attachment, growth and/or survival of challenging organisms in competitive environments. The production of these compounds is particularly important in surface attached strains and in those in biofilms. The wide array of compounds produced by marine bacteria as an adaptive response to demanding conditions makes them suitable candidates for screening of compounds with commercially interesting biological functions. Biosurfactants produced by marine bacteria may be helpful to increase mass transfer in different industrial processes and in the bioremediation of hydrocarbon-contaminated sites. Siderophores are necessary e.g., in the treatment of diseases with metal ion imbalance, while antifouling compounds could be used to treat man-made surfaces that are used in marine environments. New classes of antibiotics could efficiently combat bacteria resistant to the existing antibiotics. The present work aims to provide a comprehensive review of the metabolites produced by marine bacteria in order to cope with intrusive environments, and to illustrate how such metabolites can be advantageously used in several relevant areas, from bioremediation to health and pharmaceutical sectors.

Evidence of a Role for Aerobic Bacteria in High Magnesium Carbonate Formation in the Evaporitic Environment of Dohat Faishakh Sabkha in Qatar

“…Bacterial activity causes local supersaturation in the microenvironment surrounding the cell, and can overcome low-temperature kinetic barriers to dolomite precipitation (Van Lith et al, 2003;Sánchez-Román et al, 2009b). In fact, microorganisms exhibit the ability to create suitable microenvironments for microbially-mediated mineralization and recycling of metabolites, which has enabled them to adapt to a wide range of environmental conditions throughout the history of Earth, as widely discussed in the literature (Dupraz et al, 2009;Vu et al, 2009;De Carvalho and Fernandes, 2010;Zhang et al, 2013). For example, the production of exopolymeric substances (EPS) may function to provide templates and/or the nucleation sites for mineral formation (Bontognali et al, 2014a).…”

An Overview on Marine Sponge-Symbiotic Bacteria as Unexhausted Sources for Natural Product Discovery

“…Marine-derived bioactive compounds have been reported to have functional roles within their symbiotic environments as well as have biotechnological uses as antimicrobials, anticancer agents, pigments, vitamins, and enzymes used in industry [141][142][143][144][145]. These compounds, that in nature are produced as a defense against competitors, predators, and pathogens [20,107,115,146] providing the host organism with competitive advantages in the environment by increasing their access to space and nutrients through elimination of the competitors [6,57,147], may exhibit antibacterial, antiviral, antifungal, antimicrobial, or cytotoxic properties that can and have been used in therapeutic agents in the pharmaceutical industry [106,148,149]. Examples of bioactive compounds produced by sponge-associated bacteria are given in Table 2.…”

“…Culture-independent methods such as molecular and metagenomic approaches on the other hand, have increased our understanding of the uncultivable microbial community composition and the metabolic pathways responsible to produce potentially beneficial compounds [6,49,63,85,113]. The most commonly utilized and well known culture-independent method of describing the total.…”

“…Terrestrial plants and microorganisms have been the largest contributors to natural product discovery, however, today these natural resources have become somewhat exhausted due to culturing and supply difficulties of the producing organism or the repetition of compounds being isolated from known prolific producers such as actinobacteria and fungi which is inefficient and costly [2,3]. Furthermore, due to the emergence and re-emergence of multi-drug resistant (MDR) microorganisms [4], the quest to find novel biologically active natural compounds from a range of other biological resources is gaining importance [5][6][7].…”

“…This makes the production of these compounds, either via aquarium culture of the invertebrate (e.g., sponge) [31] or growth of the producing microorganism under laboratory conditions, a priority. Unfortunately, such unnatural settings hamper reproducibility, especially when a particular compound of interest is targeted [6,34,35] therefore, mimicking ideal growth and production conditions is of great importance as this may aid in the challenge of supply by isolating and culturing the producing microorganism. Another exciting avenue focuses on microbial genomics targeting biosynthetic gene clusters that are responsible for producing important compounds and choosing a suitable bacterial host into which the specific genes would be cloned and the compounds expressed.…”