Hypersaline microbial mats develop through seasonal and diel fluctuations, as well as under several physicochemical variables. Hence, resident microorganisms commonly employ strategies such as the synthesis of polyhydroxyalkanoates (PHAs) in order to resist changing and stressful conditions. However, the knowledge of bacterial PHA production in hypersaline microbial mats has been limited to date, particularly in regard to medium-chain length PHAs (mcl-PHAs), which have biotechnological applications due to their plastic properties. The aim of this study was to obtain evidence for PHA production in two hypersaline microbial mats of Guerrero Negro, Mexico by searching for PHA granules and PHA synthase genes in isolated bacterial strains and environmental samples. Six PHA-producing strains were identified by 16S rRNA gene sequencing; three of them corresponded to aHalomonassp. In addition,Paracoccussp.,Planomicrobiumsp. andStaphylococcussp. were also identified as PHA producers. Presumptive PHA granules and PHA synthases genes were detected in both sampling sites. Moreover, phylogenetic analysis showed that most of the phylotypes were distantly related to putative PhaC synthases class I sequences belonging to members of the classes Alphaproteobacteria and Gammaproteobacteria distributed within eight families, with higher abundances corresponding mainly to Rhodobacteraceae and Rhodospirillaceae. This analysis also showed that PhaC synthases class II sequences were closely related to those ofPseudomonas putida, suggesting the presence of this group, which is probably involved in the production of mcl-PHA in the mats. According to our state of knowledge, this study reports for the first time the occurrence ofphaCandphaC1sequences in hypersaline microbial mats, suggesting that these ecosystems may be a novel source for the isolation of short- and medium-chain length PHA producers.

Knowledge regarding the diversity of methanogenic archaeal communities in hypersaline environments is limited because of the lack of efficient cultivation efforts as well as their low abundance and metabolic activities. In this study, we explored the microbial communities in hypersaline microbial mats. Bioinformatic analyses showed significant differences among the archaeal community structures for each studied site. Taxonomic assignment based on 16S rRNA and methyl coenzyme-M reductase (mcrA) gene sequences, as well as metagenomic analysis, corroborated the presence of Methanosarcinales. Furthermore, this study also provided evidence for the presence of Methanobacteriales, Methanomicrobiales, Methanomassiliicoccales, Candidatus Methanofastidiosales, Methanocellales, Methanococcales and Methanopyrales, although some of these were found in extremely low relative abundances. Several mcrA environmental sequences were significantly different from those previously reported and did not match with any known methanogenic archaea, suggesting the presence of specific environmental clusters of methanogenic archaea in Guerrero Negro. Based on functional inference and the detection of specific genes in the metagenome, we hypothesised that all four methanogenic pathways were able to occur in these environments. This study allowed the detection of extremely low-abundance methanogenic archaea, which were highly diverse and with unknown physiology, evidencing the presence of all methanogenic metabolic pathways rather than the sheer existence of exclusively methylotrophic methanogenic archaea in hypersaline environments.

The main fishing enterprise located in the province of Pinar del Río, Cuba, markets oyster meat packed in brine bags of 460 g. The oysters come from natural bank fisheries (mangrove and bottom oyster), and from farms (mangrove oyster). Although the capture during 2009 – 2013 showed an increasing trend (50 to > 80 t), the oyster meat yields recorded values below (3.3 – 3.9 %), the acceptable minimums (4.9 %); in addition, a decrease in meat weight was observed between the packaging and commercialization, impacting productivity. The objectives of the study were the assessment of oyster exploitation based on the meat yield, and to assess the meat loss in the final packed product. A monthly and annual yield variation analysis and their relationship between fishery type and oyster size was performed. Meanwhile, the loss of meat was analyzed by different treatments of oyster / brine proportions. Significant differences (p < 0.05) of meat yield (%) by oyster species and size with a better performance in the farmed oysters were observed. The traditional proportion of packing for commercialization (meat / brine, 391 g / 69 g = 460 g), influenced the weight-loss of meat by leakage of interstitial fluid. After the treatments with different proportions of meat / brine, the proportion 1:1 showed the least loss of meat weight. The breach of commercial size and the lack of cleanliness of the oysters before the shell removing process, impacted the meat yield analysis during 2009-2013

Hypersaline microbial mats at Guerrero Negro harbor a stratified, highly diverse community with diel metabolic changes. While oxygenic photosynthesis and sulfate reduction are the dominant bacterial metabolic processes, methylotrophic methanogenesis is the main archaeal pathway. Although these metabolic processes have been biochemically characterized, the identity and encoded metabolism of the microorganisms have been inferred only from gene‐marker data. Here, a genome‐resolved approach in both environmental, as well as experimental dark condition samples (control, H ₂ /CO ₂ , TMA, and H ₂ /CO ₂ ‐TMA) was used to stimulate less‐known anaerobic strategies, determine the metabolic potential of the main microbial players, and analyze the community. Representative metagenome‐assembled genomes (170 MAGs) were obtained, encompassing 25 bacterial and 4 archaeal phyla. The metabolic analyses of three basic elements (carbon, sulfur, nitrogen) encoded in the MAGs suggested that in environmental samples, phototrophic taxa were the main source of the organic matter that fueled most of the community. Different sulfur species acting as electron acceptors led to the metabolism of partially degraded organic matter in the lower layers of the mat. These results link and clarify the biochemical processes and microbial players, adding a novel genomic component for the ecological understanding of the microbial mats of Guerrero Negro.